Source file src/time/format.go

Documentation: time

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package time
     6  
     7  import (
     8  	"errors"
     9  	"internal/stringslite"
    10  	_ "unsafe" // for linkname
    11  )
    12  
    13  // These are predefined layouts for use in [Time.Format] and [time.Parse].
    14  // The reference time used in these layouts is the specific time stamp:
    15  //
    16  //	01/02 03:04:05PM '06 -0700
    17  //
    18  // (January 2, 15:04:05, 2006, in time zone seven hours west of GMT).
    19  // That value is recorded as the constant named [Layout], listed below. As a Unix
    20  // time, this is 1136239445. Since MST is GMT-0700, the reference would be
    21  // printed by the Unix date command as:
    22  //
    23  //	Mon Jan 2 15:04:05 MST 2006
    24  //
    25  // It is a regrettable historic error that the date uses the American convention
    26  // of putting the numerical month before the day.
    27  //
    28  // The example for Time.Format demonstrates the working of the layout string
    29  // in detail and is a good reference.
    30  //
    31  // Note that the [RFC822], [RFC850], and [RFC1123] formats should be applied
    32  // only to local times. Applying them to UTC times will use "UTC" as the
    33  // time zone abbreviation, while strictly speaking those RFCs require the
    34  // use of "GMT" in that case.
    35  // When using the [RFC1123] or [RFC1123Z] formats for parsing, note that these
    36  // formats define a leading zero for the day-in-month portion, which is not
    37  // strictly allowed by RFC 1123. This will result in an error when parsing
    38  // date strings that occur in the first 9 days of a given month.
    39  // In general [RFC1123Z] should be used instead of [RFC1123] for servers
    40  // that insist on that format, and [RFC3339] should be preferred for new protocols.
    41  // [RFC3339], [RFC822], [RFC822Z], [RFC1123], and [RFC1123Z] are useful for formatting;
    42  // when used with time.Parse they do not accept all the time formats
    43  // permitted by the RFCs and they do accept time formats not formally defined.
    44  // The [RFC3339Nano] format removes trailing zeros from the seconds field
    45  // and thus may not sort correctly once formatted.
    46  //
    47  // Most programs can use one of the defined constants as the layout passed to
    48  // Format or Parse. The rest of this comment can be ignored unless you are
    49  // creating a custom layout string.
    50  //
    51  // To define your own format, write down what the reference time would look like
    52  // formatted your way; see the values of constants like [ANSIC], [StampMicro] or
    53  // [Kitchen] for examples. The model is to demonstrate what the reference time
    54  // looks like so that the Format and Parse methods can apply the same
    55  // transformation to a general time value.
    56  //
    57  // Here is a summary of the components of a layout string. Each element shows by
    58  // example the formatting of an element of the reference time. Only these values
    59  // are recognized. Text in the layout string that is not recognized as part of
    60  // the reference time is echoed verbatim during Format and expected to appear
    61  // verbatim in the input to Parse.
    62  //
    63  //	Year: "2006" "06"
    64  //	Month: "Jan" "January" "01" "1"
    65  //	Day of the week: "Mon" "Monday"
    66  //	Day of the month: "2" "_2" "02"
    67  //	Day of the year: "__2" "002"
    68  //	Hour: "15" "3" "03" (PM or AM)
    69  //	Minute: "4" "04"
    70  //	Second: "5" "05"
    71  //	AM/PM mark: "PM"
    72  //
    73  // Numeric time zone offsets format as follows:
    74  //
    75  //	"-0700"     ±hhmm
    76  //	"-07:00"    ±hh:mm
    77  //	"-07"       ±hh
    78  //	"-070000"   ±hhmmss
    79  //	"-07:00:00" ±hh:mm:ss
    80  //
    81  // Replacing the sign in the format with a Z triggers
    82  // the ISO 8601 behavior of printing Z instead of an
    83  // offset for the UTC zone. Thus:
    84  //
    85  //	"Z0700"      Z or ±hhmm
    86  //	"Z07:00"     Z or ±hh:mm
    87  //	"Z07"        Z or ±hh
    88  //	"Z070000"    Z or ±hhmmss
    89  //	"Z07:00:00"  Z or ±hh:mm:ss
    90  //
    91  // Within the format string, the underscores in "_2" and "__2" represent spaces
    92  // that may be replaced by digits if the following number has multiple digits,
    93  // for compatibility with fixed-width Unix time formats. A leading zero represents
    94  // a zero-padded value.
    95  //
    96  // The formats __2 and 002 are space-padded and zero-padded
    97  // three-character day of year; there is no unpadded day of year format.
    98  //
    99  // A comma or decimal point followed by one or more zeros represents
   100  // a fractional second, printed to the given number of decimal places.
   101  // A comma or decimal point followed by one or more nines represents
   102  // a fractional second, printed to the given number of decimal places, with
   103  // trailing zeros removed.
   104  // For example "15:04:05,000" or "15:04:05.000" formats or parses with
   105  // millisecond precision.
   106  //
   107  // Some valid layouts are invalid time values for time.Parse, due to formats
   108  // such as _ for space padding and Z for zone information.
   109  const (
   110  	Layout      = "01/02 03:04:05PM '06 -0700" // The reference time, in numerical order.
   111  	ANSIC       = "Mon Jan _2 15:04:05 2006"
   112  	UnixDate    = "Mon Jan _2 15:04:05 MST 2006"
   113  	RubyDate    = "Mon Jan 02 15:04:05 -0700 2006"
   114  	RFC822      = "02 Jan 06 15:04 MST"
   115  	RFC822Z     = "02 Jan 06 15:04 -0700" // RFC822 with numeric zone
   116  	RFC850      = "Monday, 02-Jan-06 15:04:05 MST"
   117  	RFC1123     = "Mon, 02 Jan 2006 15:04:05 MST"
   118  	RFC1123Z    = "Mon, 02 Jan 2006 15:04:05 -0700" // RFC1123 with numeric zone
   119  	RFC3339     = "2006-01-02T15:04:05Z07:00"
   120  	RFC3339Nano = "2006-01-02T15:04:05.999999999Z07:00"
   121  	Kitchen     = "3:04PM"
   122  	// Handy time stamps.
   123  	Stamp      = "Jan _2 15:04:05"
   124  	StampMilli = "Jan _2 15:04:05.000"
   125  	StampMicro = "Jan _2 15:04:05.000000"
   126  	StampNano  = "Jan _2 15:04:05.000000000"
   127  	DateTime   = "2006-01-02 15:04:05"
   128  	DateOnly   = "2006-01-02"
   129  	TimeOnly   = "15:04:05"
   130  )
   131  
   132  const (
   133  	_                        = iota
   134  	stdLongMonth             = iota + stdNeedDate  // "January"
   135  	stdMonth                                       // "Jan"
   136  	stdNumMonth                                    // "1"
   137  	stdZeroMonth                                   // "01"
   138  	stdLongWeekDay                                 // "Monday"
   139  	stdWeekDay                                     // "Mon"
   140  	stdDay                                         // "2"
   141  	stdUnderDay                                    // "_2"
   142  	stdZeroDay                                     // "02"
   143  	stdUnderYearDay                                // "__2"
   144  	stdZeroYearDay                                 // "002"
   145  	stdHour                  = iota + stdNeedClock // "15"
   146  	stdHour12                                      // "3"
   147  	stdZeroHour12                                  // "03"
   148  	stdMinute                                      // "4"
   149  	stdZeroMinute                                  // "04"
   150  	stdSecond                                      // "5"
   151  	stdZeroSecond                                  // "05"
   152  	stdLongYear              = iota + stdNeedDate  // "2006"
   153  	stdYear                                        // "06"
   154  	stdPM                    = iota + stdNeedClock // "PM"
   155  	stdpm                                          // "pm"
   156  	stdTZ                    = iota                // "MST"
   157  	stdISO8601TZ                                   // "Z0700"  // prints Z for UTC
   158  	stdISO8601SecondsTZ                            // "Z070000"
   159  	stdISO8601ShortTZ                              // "Z07"
   160  	stdISO8601ColonTZ                              // "Z07:00" // prints Z for UTC
   161  	stdISO8601ColonSecondsTZ                       // "Z07:00:00"
   162  	stdNumTZ                                       // "-0700"  // always numeric
   163  	stdNumSecondsTz                                // "-070000"
   164  	stdNumShortTZ                                  // "-07"    // always numeric
   165  	stdNumColonTZ                                  // "-07:00" // always numeric
   166  	stdNumColonSecondsTZ                           // "-07:00:00"
   167  	stdFracSecond0                                 // ".0", ".00", ... , trailing zeros included
   168  	stdFracSecond9                                 // ".9", ".99", ..., trailing zeros omitted
   169  
   170  	stdNeedDate       = 1 << 8             // need month, day, year
   171  	stdNeedClock      = 2 << 8             // need hour, minute, second
   172  	stdArgShift       = 16                 // extra argument in high bits, above low stdArgShift
   173  	stdSeparatorShift = 28                 // extra argument in high 4 bits for fractional second separators
   174  	stdMask           = 1<<stdArgShift - 1 // mask out argument
   175  )
   176  
   177  // std0x records the std values for "01", "02", ..., "06".
   178  var std0x = [...]int{stdZeroMonth, stdZeroDay, stdZeroHour12, stdZeroMinute, stdZeroSecond, stdYear}
   179  
   180  // startsWithLowerCase reports whether the string has a lower-case letter at the beginning.
   181  // Its purpose is to prevent matching strings like "Month" when looking for "Mon".
   182  func startsWithLowerCase(str string) bool {
   183  	if len(str) == 0 {
   184  		return false
   185  	}
   186  	c := str[0]
   187  	return 'a' <= c && c <= 'z'
   188  }
   189  
   190  // nextStdChunk finds the first occurrence of a std string in
   191  // layout and returns the text before, the std string, and the text after.
   192  //
   193  // nextStdChunk should be an internal detail,
   194  // but widely used packages access it using linkname.
   195  // Notable members of the hall of shame include:
   196  //   - github.com/searKing/golang/go
   197  //
   198  // Do not remove or change the type signature.
   199  // See go.dev/issue/67401.
   200  //
   201  //go:linkname nextStdChunk
   202  func nextStdChunk(layout string) (prefix string, std int, suffix string) {
   203  	for i := 0; i < len(layout); i++ {
   204  		switch c := int(layout[i]); c {
   205  		case 'J': // January, Jan
   206  			if len(layout) >= i+3 && layout[i:i+3] == "Jan" {
   207  				if len(layout) >= i+7 && layout[i:i+7] == "January" {
   208  					return layout[0:i], stdLongMonth, layout[i+7:]
   209  				}
   210  				if !startsWithLowerCase(layout[i+3:]) {
   211  					return layout[0:i], stdMonth, layout[i+3:]
   212  				}
   213  			}
   214  
   215  		case 'M': // Monday, Mon, MST
   216  			if len(layout) >= i+3 {
   217  				if layout[i:i+3] == "Mon" {
   218  					if len(layout) >= i+6 && layout[i:i+6] == "Monday" {
   219  						return layout[0:i], stdLongWeekDay, layout[i+6:]
   220  					}
   221  					if !startsWithLowerCase(layout[i+3:]) {
   222  						return layout[0:i], stdWeekDay, layout[i+3:]
   223  					}
   224  				}
   225  				if layout[i:i+3] == "MST" {
   226  					return layout[0:i], stdTZ, layout[i+3:]
   227  				}
   228  			}
   229  
   230  		case '0': // 01, 02, 03, 04, 05, 06, 002
   231  			if len(layout) >= i+2 && '1' <= layout[i+1] && layout[i+1] <= '6' {
   232  				return layout[0:i], std0x[layout[i+1]-'1'], layout[i+2:]
   233  			}
   234  			if len(layout) >= i+3 && layout[i+1] == '0' && layout[i+2] == '2' {
   235  				return layout[0:i], stdZeroYearDay, layout[i+3:]
   236  			}
   237  
   238  		case '1': // 15, 1
   239  			if len(layout) >= i+2 && layout[i+1] == '5' {
   240  				return layout[0:i], stdHour, layout[i+2:]
   241  			}
   242  			return layout[0:i], stdNumMonth, layout[i+1:]
   243  
   244  		case '2': // 2006, 2
   245  			if len(layout) >= i+4 && layout[i:i+4] == "2006" {
   246  				return layout[0:i], stdLongYear, layout[i+4:]
   247  			}
   248  			return layout[0:i], stdDay, layout[i+1:]
   249  
   250  		case '_': // _2, _2006, __2
   251  			if len(layout) >= i+2 && layout[i+1] == '2' {
   252  				//_2006 is really a literal _, followed by stdLongYear
   253  				if len(layout) >= i+5 && layout[i+1:i+5] == "2006" {
   254  					return layout[0 : i+1], stdLongYear, layout[i+5:]
   255  				}
   256  				return layout[0:i], stdUnderDay, layout[i+2:]
   257  			}
   258  			if len(layout) >= i+3 && layout[i+1] == '_' && layout[i+2] == '2' {
   259  				return layout[0:i], stdUnderYearDay, layout[i+3:]
   260  			}
   261  
   262  		case '3':
   263  			return layout[0:i], stdHour12, layout[i+1:]
   264  
   265  		case '4':
   266  			return layout[0:i], stdMinute, layout[i+1:]
   267  
   268  		case '5':
   269  			return layout[0:i], stdSecond, layout[i+1:]
   270  
   271  		case 'P': // PM
   272  			if len(layout) >= i+2 && layout[i+1] == 'M' {
   273  				return layout[0:i], stdPM, layout[i+2:]
   274  			}
   275  
   276  		case 'p': // pm
   277  			if len(layout) >= i+2 && layout[i+1] == 'm' {
   278  				return layout[0:i], stdpm, layout[i+2:]
   279  			}
   280  
   281  		case '-': // -070000, -07:00:00, -0700, -07:00, -07
   282  			if len(layout) >= i+7 && layout[i:i+7] == "-070000" {
   283  				return layout[0:i], stdNumSecondsTz, layout[i+7:]
   284  			}
   285  			if len(layout) >= i+9 && layout[i:i+9] == "-07:00:00" {
   286  				return layout[0:i], stdNumColonSecondsTZ, layout[i+9:]
   287  			}
   288  			if len(layout) >= i+5 && layout[i:i+5] == "-0700" {
   289  				return layout[0:i], stdNumTZ, layout[i+5:]
   290  			}
   291  			if len(layout) >= i+6 && layout[i:i+6] == "-07:00" {
   292  				return layout[0:i], stdNumColonTZ, layout[i+6:]
   293  			}
   294  			if len(layout) >= i+3 && layout[i:i+3] == "-07" {
   295  				return layout[0:i], stdNumShortTZ, layout[i+3:]
   296  			}
   297  
   298  		case 'Z': // Z070000, Z07:00:00, Z0700, Z07:00,
   299  			if len(layout) >= i+7 && layout[i:i+7] == "Z070000" {
   300  				return layout[0:i], stdISO8601SecondsTZ, layout[i+7:]
   301  			}
   302  			if len(layout) >= i+9 && layout[i:i+9] == "Z07:00:00" {
   303  				return layout[0:i], stdISO8601ColonSecondsTZ, layout[i+9:]
   304  			}
   305  			if len(layout) >= i+5 && layout[i:i+5] == "Z0700" {
   306  				return layout[0:i], stdISO8601TZ, layout[i+5:]
   307  			}
   308  			if len(layout) >= i+6 && layout[i:i+6] == "Z07:00" {
   309  				return layout[0:i], stdISO8601ColonTZ, layout[i+6:]
   310  			}
   311  			if len(layout) >= i+3 && layout[i:i+3] == "Z07" {
   312  				return layout[0:i], stdISO8601ShortTZ, layout[i+3:]
   313  			}
   314  
   315  		case '.', ',': // ,000, or .000, or ,999, or .999 - repeated digits for fractional seconds.
   316  			if i+1 < len(layout) && (layout[i+1] == '0' || layout[i+1] == '9') {
   317  				ch := layout[i+1]
   318  				j := i + 1
   319  				for j < len(layout) && layout[j] == ch {
   320  					j++
   321  				}
   322  				// String of digits must end here - only fractional second is all digits.
   323  				if !isDigit(layout, j) {
   324  					code := stdFracSecond0
   325  					if layout[i+1] == '9' {
   326  						code = stdFracSecond9
   327  					}
   328  					std := stdFracSecond(code, j-(i+1), c)
   329  					return layout[0:i], std, layout[j:]
   330  				}
   331  			}
   332  		}
   333  	}
   334  	return layout, 0, ""
   335  }
   336  
   337  var longDayNames = []string{
   338  	"Sunday",
   339  	"Monday",
   340  	"Tuesday",
   341  	"Wednesday",
   342  	"Thursday",
   343  	"Friday",
   344  	"Saturday",
   345  }
   346  
   347  var shortDayNames = []string{
   348  	"Sun",
   349  	"Mon",
   350  	"Tue",
   351  	"Wed",
   352  	"Thu",
   353  	"Fri",
   354  	"Sat",
   355  }
   356  
   357  var shortMonthNames = []string{
   358  	"Jan",
   359  	"Feb",
   360  	"Mar",
   361  	"Apr",
   362  	"May",
   363  	"Jun",
   364  	"Jul",
   365  	"Aug",
   366  	"Sep",
   367  	"Oct",
   368  	"Nov",
   369  	"Dec",
   370  }
   371  
   372  var longMonthNames = []string{
   373  	"January",
   374  	"February",
   375  	"March",
   376  	"April",
   377  	"May",
   378  	"June",
   379  	"July",
   380  	"August",
   381  	"September",
   382  	"October",
   383  	"November",
   384  	"December",
   385  }
   386  
   387  // match reports whether s1 and s2 match ignoring case.
   388  // It is assumed s1 and s2 are the same length.
   389  func match(s1, s2 string) bool {
   390  	for i := 0; i < len(s1); i++ {
   391  		c1 := s1[i]
   392  		c2 := s2[i]
   393  		if c1 != c2 {
   394  			// Switch to lower-case; 'a'-'A' is known to be a single bit.
   395  			c1 |= 'a' - 'A'
   396  			c2 |= 'a' - 'A'
   397  			if c1 != c2 || c1 < 'a' || c1 > 'z' {
   398  				return false
   399  			}
   400  		}
   401  	}
   402  	return true
   403  }
   404  
   405  func lookup(tab []string, val string) (int, string, error) {
   406  	for i, v := range tab {
   407  		if len(val) >= len(v) && match(val[0:len(v)], v) {
   408  			return i, val[len(v):], nil
   409  		}
   410  	}
   411  	return -1, val, errBad
   412  }
   413  
   414  // appendInt appends the decimal form of x to b and returns the result.
   415  // If the decimal form (excluding sign) is shorter than width, the result is padded with leading 0's.
   416  // Duplicates functionality in strconv, but avoids dependency.
   417  func appendInt(b []byte, x int, width int) []byte {
   418  	u := uint(x)
   419  	if x < 0 {
   420  		b = append(b, '-')
   421  		u = uint(-x)
   422  	}
   423  
   424  	// 2-digit and 4-digit fields are the most common in time formats.
   425  	utod := func(u uint) byte { return '0' + byte(u) }
   426  	switch {
   427  	case width == 2 && u < 1e2:
   428  		return append(b, utod(u/1e1), utod(u%1e1))
   429  	case width == 4 && u < 1e4:
   430  		return append(b, utod(u/1e3), utod(u/1e2%1e1), utod(u/1e1%1e1), utod(u%1e1))
   431  	}
   432  
   433  	// Compute the number of decimal digits.
   434  	var n int
   435  	if u == 0 {
   436  		n = 1
   437  	}
   438  	for u2 := u; u2 > 0; u2 /= 10 {
   439  		n++
   440  	}
   441  
   442  	// Add 0-padding.
   443  	for pad := width - n; pad > 0; pad-- {
   444  		b = append(b, '0')
   445  	}
   446  
   447  	// Ensure capacity.
   448  	if len(b)+n <= cap(b) {
   449  		b = b[:len(b)+n]
   450  	} else {
   451  		b = append(b, make([]byte, n)...)
   452  	}
   453  
   454  	// Assemble decimal in reverse order.
   455  	i := len(b) - 1
   456  	for u >= 10 && i > 0 {
   457  		q := u / 10
   458  		b[i] = utod(u - q*10)
   459  		u = q
   460  		i--
   461  	}
   462  	b[i] = utod(u)
   463  	return b
   464  }
   465  
   466  // Never printed, just needs to be non-nil for return by atoi.
   467  var errAtoi = errors.New("time: invalid number")
   468  
   469  // Duplicates functionality in strconv, but avoids dependency.
   470  func atoi[bytes []byte | string](s bytes) (x int, err error) {
   471  	neg := false
   472  	if len(s) > 0 && (s[0] == '-' || s[0] == '+') {
   473  		neg = s[0] == '-'
   474  		s = s[1:]
   475  	}
   476  	q, rem, err := leadingInt(s)
   477  	x = int(q)
   478  	if err != nil || len(rem) > 0 {
   479  		return 0, errAtoi
   480  	}
   481  	if neg {
   482  		x = -x
   483  	}
   484  	return x, nil
   485  }
   486  
   487  // The "std" value passed to appendNano contains two packed fields: the number of
   488  // digits after the decimal and the separator character (period or comma).
   489  // These functions pack and unpack that variable.
   490  func stdFracSecond(code, n, c int) int {
   491  	// Use 0xfff to make the failure case even more absurd.
   492  	if c == '.' {
   493  		return code | ((n & 0xfff) << stdArgShift)
   494  	}
   495  	return code | ((n & 0xfff) << stdArgShift) | 1<<stdSeparatorShift
   496  }
   497  
   498  func digitsLen(std int) int {
   499  	return (std >> stdArgShift) & 0xfff
   500  }
   501  
   502  func separator(std int) byte {
   503  	if (std >> stdSeparatorShift) == 0 {
   504  		return '.'
   505  	}
   506  	return ','
   507  }
   508  
   509  // appendNano appends a fractional second, as nanoseconds, to b
   510  // and returns the result. The nanosec must be within [0, 999999999].
   511  func appendNano(b []byte, nanosec int, std int) []byte {
   512  	trim := std&stdMask == stdFracSecond9
   513  	n := digitsLen(std)
   514  	if trim && (n == 0 || nanosec == 0) {
   515  		return b
   516  	}
   517  	dot := separator(std)
   518  	b = append(b, dot)
   519  	b = appendInt(b, nanosec, 9)
   520  	if n < 9 {
   521  		b = b[:len(b)-9+n]
   522  	}
   523  	if trim {
   524  		for len(b) > 0 && b[len(b)-1] == '0' {
   525  			b = b[:len(b)-1]
   526  		}
   527  		if len(b) > 0 && b[len(b)-1] == dot {
   528  			b = b[:len(b)-1]
   529  		}
   530  	}
   531  	return b
   532  }
   533  
   534  // String returns the time formatted using the format string
   535  //
   536  //	"2006-01-02 15:04:05.999999999 -0700 MST"
   537  //
   538  // If the time has a monotonic clock reading, the returned string
   539  // includes a final field "m=±<value>", where value is the monotonic
   540  // clock reading formatted as a decimal number of seconds.
   541  //
   542  // The returned string is meant for debugging; for a stable serialized
   543  // representation, use t.MarshalText, t.MarshalBinary, or t.Format
   544  // with an explicit format string.
   545  func (t Time) String() string {
   546  	s := t.Format("2006-01-02 15:04:05.999999999 -0700 MST")
   547  
   548  	// Format monotonic clock reading as m=±ddd.nnnnnnnnn.
   549  	if t.wall&hasMonotonic != 0 {
   550  		m2 := uint64(t.ext)
   551  		sign := byte('+')
   552  		if t.ext < 0 {
   553  			sign = '-'
   554  			m2 = -m2
   555  		}
   556  		m1, m2 := m2/1e9, m2%1e9
   557  		m0, m1 := m1/1e9, m1%1e9
   558  		buf := make([]byte, 0, 24)
   559  		buf = append(buf, " m="...)
   560  		buf = append(buf, sign)
   561  		wid := 0
   562  		if m0 != 0 {
   563  			buf = appendInt(buf, int(m0), 0)
   564  			wid = 9
   565  		}
   566  		buf = appendInt(buf, int(m1), wid)
   567  		buf = append(buf, '.')
   568  		buf = appendInt(buf, int(m2), 9)
   569  		s += string(buf)
   570  	}
   571  	return s
   572  }
   573  
   574  // GoString implements [fmt.GoStringer] and formats t to be printed in Go source
   575  // code.
   576  func (t Time) GoString() string {
   577  	abs := t.abs()
   578  	year, month, day, _ := absDate(abs, true)
   579  	hour, minute, second := absClock(abs)
   580  
   581  	buf := make([]byte, 0, len("time.Date(9999, time.September, 31, 23, 59, 59, 999999999, time.Local)"))
   582  	buf = append(buf, "time.Date("...)
   583  	buf = appendInt(buf, year, 0)
   584  	if January <= month && month <= December {
   585  		buf = append(buf, ", time."...)
   586  		buf = append(buf, longMonthNames[month-1]...)
   587  	} else {
   588  		// It's difficult to construct a time.Time with a date outside the
   589  		// standard range but we might as well try to handle the case.
   590  		buf = appendInt(buf, int(month), 0)
   591  	}
   592  	buf = append(buf, ", "...)
   593  	buf = appendInt(buf, day, 0)
   594  	buf = append(buf, ", "...)
   595  	buf = appendInt(buf, hour, 0)
   596  	buf = append(buf, ", "...)
   597  	buf = appendInt(buf, minute, 0)
   598  	buf = append(buf, ", "...)
   599  	buf = appendInt(buf, second, 0)
   600  	buf = append(buf, ", "...)
   601  	buf = appendInt(buf, t.Nanosecond(), 0)
   602  	buf = append(buf, ", "...)
   603  	switch loc := t.Location(); loc {
   604  	case UTC, nil:
   605  		buf = append(buf, "time.UTC"...)
   606  	case Local:
   607  		buf = append(buf, "time.Local"...)
   608  	default:
   609  		// there are several options for how we could display this, none of
   610  		// which are great:
   611  		//
   612  		// - use Location(loc.name), which is not technically valid syntax
   613  		// - use LoadLocation(loc.name), which will cause a syntax error when
   614  		// embedded and also would require us to escape the string without
   615  		// importing fmt or strconv
   616  		// - try to use FixedZone, which would also require escaping the name
   617  		// and would represent e.g. "America/Los_Angeles" daylight saving time
   618  		// shifts inaccurately
   619  		// - use the pointer format, which is no worse than you'd get with the
   620  		// old fmt.Sprintf("%#v", t) format.
   621  		//
   622  		// Of these, Location(loc.name) is the least disruptive. This is an edge
   623  		// case we hope not to hit too often.
   624  		buf = append(buf, `time.Location(`...)
   625  		buf = append(buf, quote(loc.name)...)
   626  		buf = append(buf, ')')
   627  	}
   628  	buf = append(buf, ')')
   629  	return string(buf)
   630  }
   631  
   632  // Format returns a textual representation of the time value formatted according
   633  // to the layout defined by the argument. See the documentation for the
   634  // constant called [Layout] to see how to represent the layout format.
   635  //
   636  // The executable example for [Time.Format] demonstrates the working
   637  // of the layout string in detail and is a good reference.
   638  func (t Time) Format(layout string) string {
   639  	const bufSize = 64
   640  	var b []byte
   641  	max := len(layout) + 10
   642  	if max < bufSize {
   643  		var buf [bufSize]byte
   644  		b = buf[:0]
   645  	} else {
   646  		b = make([]byte, 0, max)
   647  	}
   648  	b = t.AppendFormat(b, layout)
   649  	return string(b)
   650  }
   651  
   652  // AppendFormat is like [Time.Format] but appends the textual
   653  // representation to b and returns the extended buffer.
   654  func (t Time) AppendFormat(b []byte, layout string) []byte {
   655  	// Optimize for RFC3339 as it accounts for over half of all representations.
   656  	switch layout {
   657  	case RFC3339:
   658  		return t.appendFormatRFC3339(b, false)
   659  	case RFC3339Nano:
   660  		return t.appendFormatRFC3339(b, true)
   661  	default:
   662  		return t.appendFormat(b, layout)
   663  	}
   664  }
   665  
   666  func (t Time) appendFormat(b []byte, layout string) []byte {
   667  	var (
   668  		name, offset, abs = t.locabs()
   669  
   670  		year  int = -1
   671  		month Month
   672  		day   int
   673  		yday  int
   674  		hour  int = -1
   675  		min   int
   676  		sec   int
   677  	)
   678  
   679  	// Each iteration generates one std value.
   680  	for layout != "" {
   681  		prefix, std, suffix := nextStdChunk(layout)
   682  		if prefix != "" {
   683  			b = append(b, prefix...)
   684  		}
   685  		if std == 0 {
   686  			break
   687  		}
   688  		layout = suffix
   689  
   690  		// Compute year, month, day if needed.
   691  		if year < 0 && std&stdNeedDate != 0 {
   692  			year, month, day, yday = absDate(abs, true)
   693  			yday++
   694  		}
   695  
   696  		// Compute hour, minute, second if needed.
   697  		if hour < 0 && std&stdNeedClock != 0 {
   698  			hour, min, sec = absClock(abs)
   699  		}
   700  
   701  		switch std & stdMask {
   702  		case stdYear:
   703  			y := year
   704  			if y < 0 {
   705  				y = -y
   706  			}
   707  			b = appendInt(b, y%100, 2)
   708  		case stdLongYear:
   709  			b = appendInt(b, year, 4)
   710  		case stdMonth:
   711  			b = append(b, month.String()[:3]...)
   712  		case stdLongMonth:
   713  			m := month.String()
   714  			b = append(b, m...)
   715  		case stdNumMonth:
   716  			b = appendInt(b, int(month), 0)
   717  		case stdZeroMonth:
   718  			b = appendInt(b, int(month), 2)
   719  		case stdWeekDay:
   720  			b = append(b, absWeekday(abs).String()[:3]...)
   721  		case stdLongWeekDay:
   722  			s := absWeekday(abs).String()
   723  			b = append(b, s...)
   724  		case stdDay:
   725  			b = appendInt(b, day, 0)
   726  		case stdUnderDay:
   727  			if day < 10 {
   728  				b = append(b, ' ')
   729  			}
   730  			b = appendInt(b, day, 0)
   731  		case stdZeroDay:
   732  			b = appendInt(b, day, 2)
   733  		case stdUnderYearDay:
   734  			if yday < 100 {
   735  				b = append(b, ' ')
   736  				if yday < 10 {
   737  					b = append(b, ' ')
   738  				}
   739  			}
   740  			b = appendInt(b, yday, 0)
   741  		case stdZeroYearDay:
   742  			b = appendInt(b, yday, 3)
   743  		case stdHour:
   744  			b = appendInt(b, hour, 2)
   745  		case stdHour12:
   746  			// Noon is 12PM, midnight is 12AM.
   747  			hr := hour % 12
   748  			if hr == 0 {
   749  				hr = 12
   750  			}
   751  			b = appendInt(b, hr, 0)
   752  		case stdZeroHour12:
   753  			// Noon is 12PM, midnight is 12AM.
   754  			hr := hour % 12
   755  			if hr == 0 {
   756  				hr = 12
   757  			}
   758  			b = appendInt(b, hr, 2)
   759  		case stdMinute:
   760  			b = appendInt(b, min, 0)
   761  		case stdZeroMinute:
   762  			b = appendInt(b, min, 2)
   763  		case stdSecond:
   764  			b = appendInt(b, sec, 0)
   765  		case stdZeroSecond:
   766  			b = appendInt(b, sec, 2)
   767  		case stdPM:
   768  			if hour >= 12 {
   769  				b = append(b, "PM"...)
   770  			} else {
   771  				b = append(b, "AM"...)
   772  			}
   773  		case stdpm:
   774  			if hour >= 12 {
   775  				b = append(b, "pm"...)
   776  			} else {
   777  				b = append(b, "am"...)
   778  			}
   779  		case stdISO8601TZ, stdISO8601ColonTZ, stdISO8601SecondsTZ, stdISO8601ShortTZ, stdISO8601ColonSecondsTZ, stdNumTZ, stdNumColonTZ, stdNumSecondsTz, stdNumShortTZ, stdNumColonSecondsTZ:
   780  			// Ugly special case. We cheat and take the "Z" variants
   781  			// to mean "the time zone as formatted for ISO 8601".
   782  			if offset == 0 && (std == stdISO8601TZ || std == stdISO8601ColonTZ || std == stdISO8601SecondsTZ || std == stdISO8601ShortTZ || std == stdISO8601ColonSecondsTZ) {
   783  				b = append(b, 'Z')
   784  				break
   785  			}
   786  			zone := offset / 60 // convert to minutes
   787  			absoffset := offset
   788  			if zone < 0 {
   789  				b = append(b, '-')
   790  				zone = -zone
   791  				absoffset = -absoffset
   792  			} else {
   793  				b = append(b, '+')
   794  			}
   795  			b = appendInt(b, zone/60, 2)
   796  			if std == stdISO8601ColonTZ || std == stdNumColonTZ || std == stdISO8601ColonSecondsTZ || std == stdNumColonSecondsTZ {
   797  				b = append(b, ':')
   798  			}
   799  			if std != stdNumShortTZ && std != stdISO8601ShortTZ {
   800  				b = appendInt(b, zone%60, 2)
   801  			}
   802  
   803  			// append seconds if appropriate
   804  			if std == stdISO8601SecondsTZ || std == stdNumSecondsTz || std == stdNumColonSecondsTZ || std == stdISO8601ColonSecondsTZ {
   805  				if std == stdNumColonSecondsTZ || std == stdISO8601ColonSecondsTZ {
   806  					b = append(b, ':')
   807  				}
   808  				b = appendInt(b, absoffset%60, 2)
   809  			}
   810  
   811  		case stdTZ:
   812  			if name != "" {
   813  				b = append(b, name...)
   814  				break
   815  			}
   816  			// No time zone known for this time, but we must print one.
   817  			// Use the -0700 format.
   818  			zone := offset / 60 // convert to minutes
   819  			if zone < 0 {
   820  				b = append(b, '-')
   821  				zone = -zone
   822  			} else {
   823  				b = append(b, '+')
   824  			}
   825  			b = appendInt(b, zone/60, 2)
   826  			b = appendInt(b, zone%60, 2)
   827  		case stdFracSecond0, stdFracSecond9:
   828  			b = appendNano(b, t.Nanosecond(), std)
   829  		}
   830  	}
   831  	return b
   832  }
   833  
   834  var errBad = errors.New("bad value for field") // placeholder not passed to user
   835  
   836  // ParseError describes a problem parsing a time string.
   837  type ParseError struct {
   838  	Layout     string
   839  	Value      string
   840  	LayoutElem string
   841  	ValueElem  string
   842  	Message    string
   843  }
   844  
   845  // newParseError creates a new ParseError.
   846  // The provided value and valueElem are cloned to avoid escaping their values.
   847  func newParseError(layout, value, layoutElem, valueElem, message string) *ParseError {
   848  	valueCopy := stringslite.Clone(value)
   849  	valueElemCopy := stringslite.Clone(valueElem)
   850  	return &ParseError{layout, valueCopy, layoutElem, valueElemCopy, message}
   851  }
   852  
   853  // These are borrowed from unicode/utf8 and strconv and replicate behavior in
   854  // that package, since we can't take a dependency on either.
   855  const (
   856  	lowerhex  = "0123456789abcdef"
   857  	runeSelf  = 0x80
   858  	runeError = '\uFFFD'
   859  )
   860  
   861  func quote(s string) string {
   862  	buf := make([]byte, 1, len(s)+2) // slice will be at least len(s) + quotes
   863  	buf[0] = '"'
   864  	for i, c := range s {
   865  		if c >= runeSelf || c < ' ' {
   866  			// This means you are asking us to parse a time.Duration or
   867  			// time.Location with unprintable or non-ASCII characters in it.
   868  			// We don't expect to hit this case very often. We could try to
   869  			// reproduce strconv.Quote's behavior with full fidelity but
   870  			// given how rarely we expect to hit these edge cases, speed and
   871  			// conciseness are better.
   872  			var width int
   873  			if c == runeError {
   874  				width = 1
   875  				if i+2 < len(s) && s[i:i+3] == string(runeError) {
   876  					width = 3
   877  				}
   878  			} else {
   879  				width = len(string(c))
   880  			}
   881  			for j := 0; j < width; j++ {
   882  				buf = append(buf, `\x`...)
   883  				buf = append(buf, lowerhex[s[i+j]>>4])
   884  				buf = append(buf, lowerhex[s[i+j]&0xF])
   885  			}
   886  		} else {
   887  			if c == '"' || c == '\\' {
   888  				buf = append(buf, '\\')
   889  			}
   890  			buf = append(buf, string(c)...)
   891  		}
   892  	}
   893  	buf = append(buf, '"')
   894  	return string(buf)
   895  }
   896  
   897  // Error returns the string representation of a ParseError.
   898  func (e *ParseError) Error() string {
   899  	if e.Message == "" {
   900  		return "parsing time " +
   901  			quote(e.Value) + " as " +
   902  			quote(e.Layout) + ": cannot parse " +
   903  			quote(e.ValueElem) + " as " +
   904  			quote(e.LayoutElem)
   905  	}
   906  	return "parsing time " +
   907  		quote(e.Value) + e.Message
   908  }
   909  
   910  // isDigit reports whether s[i] is in range and is a decimal digit.
   911  func isDigit[bytes []byte | string](s bytes, i int) bool {
   912  	if len(s) <= i {
   913  		return false
   914  	}
   915  	c := s[i]
   916  	return '0' <= c && c <= '9'
   917  }
   918  
   919  // getnum parses s[0:1] or s[0:2] (fixed forces s[0:2])
   920  // as a decimal integer and returns the integer and the
   921  // remainder of the string.
   922  func getnum(s string, fixed bool) (int, string, error) {
   923  	if !isDigit(s, 0) {
   924  		return 0, s, errBad
   925  	}
   926  	if !isDigit(s, 1) {
   927  		if fixed {
   928  			return 0, s, errBad
   929  		}
   930  		return int(s[0] - '0'), s[1:], nil
   931  	}
   932  	return int(s[0]-'0')*10 + int(s[1]-'0'), s[2:], nil
   933  }
   934  
   935  // getnum3 parses s[0:1], s[0:2], or s[0:3] (fixed forces s[0:3])
   936  // as a decimal integer and returns the integer and the remainder
   937  // of the string.
   938  func getnum3(s string, fixed bool) (int, string, error) {
   939  	var n, i int
   940  	for i = 0; i < 3 && isDigit(s, i); i++ {
   941  		n = n*10 + int(s[i]-'0')
   942  	}
   943  	if i == 0 || fixed && i != 3 {
   944  		return 0, s, errBad
   945  	}
   946  	return n, s[i:], nil
   947  }
   948  
   949  func cutspace(s string) string {
   950  	for len(s) > 0 && s[0] == ' ' {
   951  		s = s[1:]
   952  	}
   953  	return s
   954  }
   955  
   956  // skip removes the given prefix from value,
   957  // treating runs of space characters as equivalent.
   958  func skip(value, prefix string) (string, error) {
   959  	for len(prefix) > 0 {
   960  		if prefix[0] == ' ' {
   961  			if len(value) > 0 && value[0] != ' ' {
   962  				return value, errBad
   963  			}
   964  			prefix = cutspace(prefix)
   965  			value = cutspace(value)
   966  			continue
   967  		}
   968  		if len(value) == 0 || value[0] != prefix[0] {
   969  			return value, errBad
   970  		}
   971  		prefix = prefix[1:]
   972  		value = value[1:]
   973  	}
   974  	return value, nil
   975  }
   976  
   977  // Parse parses a formatted string and returns the time value it represents.
   978  // See the documentation for the constant called [Layout] to see how to
   979  // represent the format. The second argument must be parseable using
   980  // the format string (layout) provided as the first argument.
   981  //
   982  // The example for [Time.Format] demonstrates the working of the layout string
   983  // in detail and is a good reference.
   984  //
   985  // When parsing (only), the input may contain a fractional second
   986  // field immediately after the seconds field, even if the layout does not
   987  // signify its presence. In that case either a comma or a decimal point
   988  // followed by a maximal series of digits is parsed as a fractional second.
   989  // Fractional seconds are truncated to nanosecond precision.
   990  //
   991  // Elements omitted from the layout are assumed to be zero or, when
   992  // zero is impossible, one, so parsing "3:04pm" returns the time
   993  // corresponding to Jan 1, year 0, 15:04:00 UTC (note that because the year is
   994  // 0, this time is before the zero Time).
   995  // Years must be in the range 0000..9999. The day of the week is checked
   996  // for syntax but it is otherwise ignored.
   997  //
   998  // For layouts specifying the two-digit year 06, a value NN >= 69 will be treated
   999  // as 19NN and a value NN < 69 will be treated as 20NN.
  1000  //
  1001  // The remainder of this comment describes the handling of time zones.
  1002  //
  1003  // In the absence of a time zone indicator, Parse returns a time in UTC.
  1004  //
  1005  // When parsing a time with a zone offset like -0700, if the offset corresponds
  1006  // to a time zone used by the current location ([Local]), then Parse uses that
  1007  // location and zone in the returned time. Otherwise it records the time as
  1008  // being in a fabricated location with time fixed at the given zone offset.
  1009  //
  1010  // When parsing a time with a zone abbreviation like MST, if the zone abbreviation
  1011  // has a defined offset in the current location, then that offset is used.
  1012  // The zone abbreviation "UTC" is recognized as UTC regardless of location.
  1013  // If the zone abbreviation is unknown, Parse records the time as being
  1014  // in a fabricated location with the given zone abbreviation and a zero offset.
  1015  // This choice means that such a time can be parsed and reformatted with the
  1016  // same layout losslessly, but the exact instant used in the representation will
  1017  // differ by the actual zone offset. To avoid such problems, prefer time layouts
  1018  // that use a numeric zone offset, or use [ParseInLocation].
  1019  func Parse(layout, value string) (Time, error) {
  1020  	// Optimize for RFC3339 as it accounts for over half of all representations.
  1021  	if layout == RFC3339 || layout == RFC3339Nano {
  1022  		if t, ok := parseRFC3339(value, Local); ok {
  1023  			return t, nil
  1024  		}
  1025  	}
  1026  	return parse(layout, value, UTC, Local)
  1027  }
  1028  
  1029  // ParseInLocation is like Parse but differs in two important ways.
  1030  // First, in the absence of time zone information, Parse interprets a time as UTC;
  1031  // ParseInLocation interprets the time as in the given location.
  1032  // Second, when given a zone offset or abbreviation, Parse tries to match it
  1033  // against the Local location; ParseInLocation uses the given location.
  1034  func ParseInLocation(layout, value string, loc *Location) (Time, error) {
  1035  	// Optimize for RFC3339 as it accounts for over half of all representations.
  1036  	if layout == RFC3339 || layout == RFC3339Nano {
  1037  		if t, ok := parseRFC3339(value, loc); ok {
  1038  			return t, nil
  1039  		}
  1040  	}
  1041  	return parse(layout, value, loc, loc)
  1042  }
  1043  
  1044  func parse(layout, value string, defaultLocation, local *Location) (Time, error) {
  1045  	alayout, avalue := layout, value
  1046  	rangeErrString := "" // set if a value is out of range
  1047  	amSet := false       // do we need to subtract 12 from the hour for midnight?
  1048  	pmSet := false       // do we need to add 12 to the hour?
  1049  
  1050  	// Time being constructed.
  1051  	var (
  1052  		year       int
  1053  		month      int = -1
  1054  		day        int = -1
  1055  		yday       int = -1
  1056  		hour       int
  1057  		min        int
  1058  		sec        int
  1059  		nsec       int
  1060  		z          *Location
  1061  		zoneOffset int = -1
  1062  		zoneName   string
  1063  	)
  1064  
  1065  	// Each iteration processes one std value.
  1066  	for {
  1067  		var err error
  1068  		prefix, std, suffix := nextStdChunk(layout)
  1069  		stdstr := layout[len(prefix) : len(layout)-len(suffix)]
  1070  		value, err = skip(value, prefix)
  1071  		if err != nil {
  1072  			return Time{}, newParseError(alayout, avalue, prefix, value, "")
  1073  		}
  1074  		if std == 0 {
  1075  			if len(value) != 0 {
  1076  				return Time{}, newParseError(alayout, avalue, "", value, ": extra text: "+quote(value))
  1077  			}
  1078  			break
  1079  		}
  1080  		layout = suffix
  1081  		var p string
  1082  		hold := value
  1083  		switch std & stdMask {
  1084  		case stdYear:
  1085  			if len(value) < 2 {
  1086  				err = errBad
  1087  				break
  1088  			}
  1089  			p, value = value[0:2], value[2:]
  1090  			year, err = atoi(p)
  1091  			if err != nil {
  1092  				break
  1093  			}
  1094  			if year >= 69 { // Unix time starts Dec 31 1969 in some time zones
  1095  				year += 1900
  1096  			} else {
  1097  				year += 2000
  1098  			}
  1099  		case stdLongYear:
  1100  			if len(value) < 4 || !isDigit(value, 0) {
  1101  				err = errBad
  1102  				break
  1103  			}
  1104  			p, value = value[0:4], value[4:]
  1105  			year, err = atoi(p)
  1106  		case stdMonth:
  1107  			month, value, err = lookup(shortMonthNames, value)
  1108  			month++
  1109  		case stdLongMonth:
  1110  			month, value, err = lookup(longMonthNames, value)
  1111  			month++
  1112  		case stdNumMonth, stdZeroMonth:
  1113  			month, value, err = getnum(value, std == stdZeroMonth)
  1114  			if err == nil && (month <= 0 || 12 < month) {
  1115  				rangeErrString = "month"
  1116  			}
  1117  		case stdWeekDay:
  1118  			// Ignore weekday except for error checking.
  1119  			_, value, err = lookup(shortDayNames, value)
  1120  		case stdLongWeekDay:
  1121  			_, value, err = lookup(longDayNames, value)
  1122  		case stdDay, stdUnderDay, stdZeroDay:
  1123  			if std == stdUnderDay && len(value) > 0 && value[0] == ' ' {
  1124  				value = value[1:]
  1125  			}
  1126  			day, value, err = getnum(value, std == stdZeroDay)
  1127  			// Note that we allow any one- or two-digit day here.
  1128  			// The month, day, year combination is validated after we've completed parsing.
  1129  		case stdUnderYearDay, stdZeroYearDay:
  1130  			for i := 0; i < 2; i++ {
  1131  				if std == stdUnderYearDay && len(value) > 0 && value[0] == ' ' {
  1132  					value = value[1:]
  1133  				}
  1134  			}
  1135  			yday, value, err = getnum3(value, std == stdZeroYearDay)
  1136  			// Note that we allow any one-, two-, or three-digit year-day here.
  1137  			// The year-day, year combination is validated after we've completed parsing.
  1138  		case stdHour:
  1139  			hour, value, err = getnum(value, false)
  1140  			if hour < 0 || 24 <= hour {
  1141  				rangeErrString = "hour"
  1142  			}
  1143  		case stdHour12, stdZeroHour12:
  1144  			hour, value, err = getnum(value, std == stdZeroHour12)
  1145  			if hour < 0 || 12 < hour {
  1146  				rangeErrString = "hour"
  1147  			}
  1148  		case stdMinute, stdZeroMinute:
  1149  			min, value, err = getnum(value, std == stdZeroMinute)
  1150  			if min < 0 || 60 <= min {
  1151  				rangeErrString = "minute"
  1152  			}
  1153  		case stdSecond, stdZeroSecond:
  1154  			sec, value, err = getnum(value, std == stdZeroSecond)
  1155  			if err != nil {
  1156  				break
  1157  			}
  1158  			if sec < 0 || 60 <= sec {
  1159  				rangeErrString = "second"
  1160  				break
  1161  			}
  1162  			// Special case: do we have a fractional second but no
  1163  			// fractional second in the format?
  1164  			if len(value) >= 2 && commaOrPeriod(value[0]) && isDigit(value, 1) {
  1165  				_, std, _ = nextStdChunk(layout)
  1166  				std &= stdMask
  1167  				if std == stdFracSecond0 || std == stdFracSecond9 {
  1168  					// Fractional second in the layout; proceed normally
  1169  					break
  1170  				}
  1171  				// No fractional second in the layout but we have one in the input.
  1172  				n := 2
  1173  				for ; n < len(value) && isDigit(value, n); n++ {
  1174  				}
  1175  				nsec, rangeErrString, err = parseNanoseconds(value, n)
  1176  				value = value[n:]
  1177  			}
  1178  		case stdPM:
  1179  			if len(value) < 2 {
  1180  				err = errBad
  1181  				break
  1182  			}
  1183  			p, value = value[0:2], value[2:]
  1184  			switch p {
  1185  			case "PM":
  1186  				pmSet = true
  1187  			case "AM":
  1188  				amSet = true
  1189  			default:
  1190  				err = errBad
  1191  			}
  1192  		case stdpm:
  1193  			if len(value) < 2 {
  1194  				err = errBad
  1195  				break
  1196  			}
  1197  			p, value = value[0:2], value[2:]
  1198  			switch p {
  1199  			case "pm":
  1200  				pmSet = true
  1201  			case "am":
  1202  				amSet = true
  1203  			default:
  1204  				err = errBad
  1205  			}
  1206  		case stdISO8601TZ, stdISO8601ShortTZ, stdISO8601ColonTZ, stdISO8601SecondsTZ, stdISO8601ColonSecondsTZ:
  1207  			if len(value) >= 1 && value[0] == 'Z' {
  1208  				value = value[1:]
  1209  				z = UTC
  1210  				break
  1211  			}
  1212  			fallthrough
  1213  		case stdNumTZ, stdNumShortTZ, stdNumColonTZ, stdNumSecondsTz, stdNumColonSecondsTZ:
  1214  			var sign, hour, min, seconds string
  1215  			if std == stdISO8601ColonTZ || std == stdNumColonTZ {
  1216  				if len(value) < 6 {
  1217  					err = errBad
  1218  					break
  1219  				}
  1220  				if value[3] != ':' {
  1221  					err = errBad
  1222  					break
  1223  				}
  1224  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[4:6], "00", value[6:]
  1225  			} else if std == stdNumShortTZ || std == stdISO8601ShortTZ {
  1226  				if len(value) < 3 {
  1227  					err = errBad
  1228  					break
  1229  				}
  1230  				sign, hour, min, seconds, value = value[0:1], value[1:3], "00", "00", value[3:]
  1231  			} else if std == stdISO8601ColonSecondsTZ || std == stdNumColonSecondsTZ {
  1232  				if len(value) < 9 {
  1233  					err = errBad
  1234  					break
  1235  				}
  1236  				if value[3] != ':' || value[6] != ':' {
  1237  					err = errBad
  1238  					break
  1239  				}
  1240  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[4:6], value[7:9], value[9:]
  1241  			} else if std == stdISO8601SecondsTZ || std == stdNumSecondsTz {
  1242  				if len(value) < 7 {
  1243  					err = errBad
  1244  					break
  1245  				}
  1246  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[3:5], value[5:7], value[7:]
  1247  			} else {
  1248  				if len(value) < 5 {
  1249  					err = errBad
  1250  					break
  1251  				}
  1252  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[3:5], "00", value[5:]
  1253  			}
  1254  			var hr, mm, ss int
  1255  			hr, _, err = getnum(hour, true)
  1256  			if err == nil {
  1257  				mm, _, err = getnum(min, true)
  1258  			}
  1259  			if err == nil {
  1260  				ss, _, err = getnum(seconds, true)
  1261  			}
  1262  
  1263  			// The range test use > rather than >=,
  1264  			// as some people do write offsets of 24 hours
  1265  			// or 60 minutes or 60 seconds.
  1266  			if hr > 24 {
  1267  				rangeErrString = "time zone offset hour"
  1268  			}
  1269  			if mm > 60 {
  1270  				rangeErrString = "time zone offset minute"
  1271  			}
  1272  			if ss > 60 {
  1273  				rangeErrString = "time zone offset second"
  1274  			}
  1275  
  1276  			zoneOffset = (hr*60+mm)*60 + ss // offset is in seconds
  1277  			switch sign[0] {
  1278  			case '+':
  1279  			case '-':
  1280  				zoneOffset = -zoneOffset
  1281  			default:
  1282  				err = errBad
  1283  			}
  1284  		case stdTZ:
  1285  			// Does it look like a time zone?
  1286  			if len(value) >= 3 && value[0:3] == "UTC" {
  1287  				z = UTC
  1288  				value = value[3:]
  1289  				break
  1290  			}
  1291  			n, ok := parseTimeZone(value)
  1292  			if !ok {
  1293  				err = errBad
  1294  				break
  1295  			}
  1296  			zoneName, value = value[:n], value[n:]
  1297  
  1298  		case stdFracSecond0:
  1299  			// stdFracSecond0 requires the exact number of digits as specified in
  1300  			// the layout.
  1301  			ndigit := 1 + digitsLen(std)
  1302  			if len(value) < ndigit {
  1303  				err = errBad
  1304  				break
  1305  			}
  1306  			nsec, rangeErrString, err = parseNanoseconds(value, ndigit)
  1307  			value = value[ndigit:]
  1308  
  1309  		case stdFracSecond9:
  1310  			if len(value) < 2 || !commaOrPeriod(value[0]) || value[1] < '0' || '9' < value[1] {
  1311  				// Fractional second omitted.
  1312  				break
  1313  			}
  1314  			// Take any number of digits, even more than asked for,
  1315  			// because it is what the stdSecond case would do.
  1316  			i := 0
  1317  			for i+1 < len(value) && '0' <= value[i+1] && value[i+1] <= '9' {
  1318  				i++
  1319  			}
  1320  			nsec, rangeErrString, err = parseNanoseconds(value, 1+i)
  1321  			value = value[1+i:]
  1322  		}
  1323  		if rangeErrString != "" {
  1324  			return Time{}, newParseError(alayout, avalue, stdstr, value, ": "+rangeErrString+" out of range")
  1325  		}
  1326  		if err != nil {
  1327  			return Time{}, newParseError(alayout, avalue, stdstr, hold, "")
  1328  		}
  1329  	}
  1330  	if pmSet && hour < 12 {
  1331  		hour += 12
  1332  	} else if amSet && hour == 12 {
  1333  		hour = 0
  1334  	}
  1335  
  1336  	// Convert yday to day, month.
  1337  	if yday >= 0 {
  1338  		var d int
  1339  		var m int
  1340  		if isLeap(year) {
  1341  			if yday == 31+29 {
  1342  				m = int(February)
  1343  				d = 29
  1344  			} else if yday > 31+29 {
  1345  				yday--
  1346  			}
  1347  		}
  1348  		if yday < 1 || yday > 365 {
  1349  			return Time{}, newParseError(alayout, avalue, "", value, ": day-of-year out of range")
  1350  		}
  1351  		if m == 0 {
  1352  			m = (yday-1)/31 + 1
  1353  			if int(daysBefore[m]) < yday {
  1354  				m++
  1355  			}
  1356  			d = yday - int(daysBefore[m-1])
  1357  		}
  1358  		// If month, day already seen, yday's m, d must match.
  1359  		// Otherwise, set them from m, d.
  1360  		if month >= 0 && month != m {
  1361  			return Time{}, newParseError(alayout, avalue, "", value, ": day-of-year does not match month")
  1362  		}
  1363  		month = m
  1364  		if day >= 0 && day != d {
  1365  			return Time{}, newParseError(alayout, avalue, "", value, ": day-of-year does not match day")
  1366  		}
  1367  		day = d
  1368  	} else {
  1369  		if month < 0 {
  1370  			month = int(January)
  1371  		}
  1372  		if day < 0 {
  1373  			day = 1
  1374  		}
  1375  	}
  1376  
  1377  	// Validate the day of the month.
  1378  	if day < 1 || day > daysIn(Month(month), year) {
  1379  		return Time{}, newParseError(alayout, avalue, "", value, ": day out of range")
  1380  	}
  1381  
  1382  	if z != nil {
  1383  		return Date(year, Month(month), day, hour, min, sec, nsec, z), nil
  1384  	}
  1385  
  1386  	if zoneOffset != -1 {
  1387  		t := Date(year, Month(month), day, hour, min, sec, nsec, UTC)
  1388  		t.addSec(-int64(zoneOffset))
  1389  
  1390  		// Look for local zone with the given offset.
  1391  		// If that zone was in effect at the given time, use it.
  1392  		name, offset, _, _, _ := local.lookup(t.unixSec())
  1393  		if offset == zoneOffset && (zoneName == "" || name == zoneName) {
  1394  			t.setLoc(local)
  1395  			return t, nil
  1396  		}
  1397  
  1398  		// Otherwise create fake zone to record offset.
  1399  		zoneNameCopy := stringslite.Clone(zoneName) // avoid leaking the input value
  1400  		t.setLoc(FixedZone(zoneNameCopy, zoneOffset))
  1401  		return t, nil
  1402  	}
  1403  
  1404  	if zoneName != "" {
  1405  		t := Date(year, Month(month), day, hour, min, sec, nsec, UTC)
  1406  		// Look for local zone with the given offset.
  1407  		// If that zone was in effect at the given time, use it.
  1408  		offset, ok := local.lookupName(zoneName, t.unixSec())
  1409  		if ok {
  1410  			t.addSec(-int64(offset))
  1411  			t.setLoc(local)
  1412  			return t, nil
  1413  		}
  1414  
  1415  		// Otherwise, create fake zone with unknown offset.
  1416  		if len(zoneName) > 3 && zoneName[:3] == "GMT" {
  1417  			offset, _ = atoi(zoneName[3:]) // Guaranteed OK by parseGMT.
  1418  			offset *= 3600
  1419  		}
  1420  		zoneNameCopy := stringslite.Clone(zoneName) // avoid leaking the input value
  1421  		t.setLoc(FixedZone(zoneNameCopy, offset))
  1422  		return t, nil
  1423  	}
  1424  
  1425  	// Otherwise, fall back to default.
  1426  	return Date(year, Month(month), day, hour, min, sec, nsec, defaultLocation), nil
  1427  }
  1428  
  1429  // parseTimeZone parses a time zone string and returns its length. Time zones
  1430  // are human-generated and unpredictable. We can't do precise error checking.
  1431  // On the other hand, for a correct parse there must be a time zone at the
  1432  // beginning of the string, so it's almost always true that there's one
  1433  // there. We look at the beginning of the string for a run of upper-case letters.
  1434  // If there are more than 5, it's an error.
  1435  // If there are 4 or 5 and the last is a T, it's a time zone.
  1436  // If there are 3, it's a time zone.
  1437  // Otherwise, other than special cases, it's not a time zone.
  1438  // GMT is special because it can have an hour offset.
  1439  func parseTimeZone(value string) (length int, ok bool) {
  1440  	if len(value) < 3 {
  1441  		return 0, false
  1442  	}
  1443  	// Special case 1: ChST and MeST are the only zones with a lower-case letter.
  1444  	if len(value) >= 4 && (value[:4] == "ChST" || value[:4] == "MeST") {
  1445  		return 4, true
  1446  	}
  1447  	// Special case 2: GMT may have an hour offset; treat it specially.
  1448  	if value[:3] == "GMT" {
  1449  		length = parseGMT(value)
  1450  		return length, true
  1451  	}
  1452  	// Special Case 3: Some time zones are not named, but have +/-00 format
  1453  	if value[0] == '+' || value[0] == '-' {
  1454  		length = parseSignedOffset(value)
  1455  		ok := length > 0 // parseSignedOffset returns 0 in case of bad input
  1456  		return length, ok
  1457  	}
  1458  	// How many upper-case letters are there? Need at least three, at most five.
  1459  	var nUpper int
  1460  	for nUpper = 0; nUpper < 6; nUpper++ {
  1461  		if nUpper >= len(value) {
  1462  			break
  1463  		}
  1464  		if c := value[nUpper]; c < 'A' || 'Z' < c {
  1465  			break
  1466  		}
  1467  	}
  1468  	switch nUpper {
  1469  	case 0, 1, 2, 6:
  1470  		return 0, false
  1471  	case 5: // Must end in T to match.
  1472  		if value[4] == 'T' {
  1473  			return 5, true
  1474  		}
  1475  	case 4:
  1476  		// Must end in T, except one special case.
  1477  		if value[3] == 'T' || value[:4] == "WITA" {
  1478  			return 4, true
  1479  		}
  1480  	case 3:
  1481  		return 3, true
  1482  	}
  1483  	return 0, false
  1484  }
  1485  
  1486  // parseGMT parses a GMT time zone. The input string is known to start "GMT".
  1487  // The function checks whether that is followed by a sign and a number in the
  1488  // range -23 through +23 excluding zero.
  1489  func parseGMT(value string) int {
  1490  	value = value[3:]
  1491  	if len(value) == 0 {
  1492  		return 3
  1493  	}
  1494  
  1495  	return 3 + parseSignedOffset(value)
  1496  }
  1497  
  1498  // parseSignedOffset parses a signed timezone offset (e.g. "+03" or "-04").
  1499  // The function checks for a signed number in the range -23 through +23 excluding zero.
  1500  // Returns length of the found offset string or 0 otherwise.
  1501  func parseSignedOffset(value string) int {
  1502  	sign := value[0]
  1503  	if sign != '-' && sign != '+' {
  1504  		return 0
  1505  	}
  1506  	x, rem, err := leadingInt(value[1:])
  1507  
  1508  	// fail if nothing consumed by leadingInt
  1509  	if err != nil || value[1:] == rem {
  1510  		return 0
  1511  	}
  1512  	if x > 23 {
  1513  		return 0
  1514  	}
  1515  	return len(value) - len(rem)
  1516  }
  1517  
  1518  func commaOrPeriod(b byte) bool {
  1519  	return b == '.' || b == ','
  1520  }
  1521  
  1522  func parseNanoseconds[bytes []byte | string](value bytes, nbytes int) (ns int, rangeErrString string, err error) {
  1523  	if !commaOrPeriod(value[0]) {
  1524  		err = errBad
  1525  		return
  1526  	}
  1527  	if nbytes > 10 {
  1528  		value = value[:10]
  1529  		nbytes = 10
  1530  	}
  1531  	if ns, err = atoi(value[1:nbytes]); err != nil {
  1532  		return
  1533  	}
  1534  	if ns < 0 {
  1535  		rangeErrString = "fractional second"
  1536  		return
  1537  	}
  1538  	// We need nanoseconds, which means scaling by the number
  1539  	// of missing digits in the format, maximum length 10.
  1540  	scaleDigits := 10 - nbytes
  1541  	for i := 0; i < scaleDigits; i++ {
  1542  		ns *= 10
  1543  	}
  1544  	return
  1545  }
  1546  
  1547  var errLeadingInt = errors.New("time: bad [0-9]*") // never printed
  1548  
  1549  // leadingInt consumes the leading [0-9]* from s.
  1550  func leadingInt[bytes []byte | string](s bytes) (x uint64, rem bytes, err error) {
  1551  	i := 0
  1552  	for ; i < len(s); i++ {
  1553  		c := s[i]
  1554  		if c < '0' || c > '9' {
  1555  			break
  1556  		}
  1557  		if x > 1<<63/10 {
  1558  			// overflow
  1559  			return 0, rem, errLeadingInt
  1560  		}
  1561  		x = x*10 + uint64(c) - '0'
  1562  		if x > 1<<63 {
  1563  			// overflow
  1564  			return 0, rem, errLeadingInt
  1565  		}
  1566  	}
  1567  	return x, s[i:], nil
  1568  }
  1569  
  1570  // leadingFraction consumes the leading [0-9]* from s.
  1571  // It is used only for fractions, so does not return an error on overflow,
  1572  // it just stops accumulating precision.
  1573  func leadingFraction(s string) (x uint64, scale float64, rem string) {
  1574  	i := 0
  1575  	scale = 1
  1576  	overflow := false
  1577  	for ; i < len(s); i++ {
  1578  		c := s[i]
  1579  		if c < '0' || c > '9' {
  1580  			break
  1581  		}
  1582  		if overflow {
  1583  			continue
  1584  		}
  1585  		if x > (1<<63-1)/10 {
  1586  			// It's possible for overflow to give a positive number, so take care.
  1587  			overflow = true
  1588  			continue
  1589  		}
  1590  		y := x*10 + uint64(c) - '0'
  1591  		if y > 1<<63 {
  1592  			overflow = true
  1593  			continue
  1594  		}
  1595  		x = y
  1596  		scale *= 10
  1597  	}
  1598  	return x, scale, s[i:]
  1599  }
  1600  
  1601  var unitMap = map[string]uint64{
  1602  	"ns": uint64(Nanosecond),
  1603  	"us": uint64(Microsecond),
  1604  	"µs": uint64(Microsecond), // U+00B5 = micro symbol
  1605  	"μs": uint64(Microsecond), // U+03BC = Greek letter mu
  1606  	"ms": uint64(Millisecond),
  1607  	"s":  uint64(Second),
  1608  	"m":  uint64(Minute),
  1609  	"h":  uint64(Hour),
  1610  }
  1611  
  1612  // ParseDuration parses a duration string.
  1613  // A duration string is a possibly signed sequence of
  1614  // decimal numbers, each with optional fraction and a unit suffix,
  1615  // such as "300ms", "-1.5h" or "2h45m".
  1616  // Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
  1617  func ParseDuration(s string) (Duration, error) {
  1618  	// [-+]?([0-9]*(\.[0-9]*)?[a-z]+)+
  1619  	orig := s
  1620  	var d uint64
  1621  	neg := false
  1622  
  1623  	// Consume [-+]?
  1624  	if s != "" {
  1625  		c := s[0]
  1626  		if c == '-' || c == '+' {
  1627  			neg = c == '-'
  1628  			s = s[1:]
  1629  		}
  1630  	}
  1631  	// Special case: if all that is left is "0", this is zero.
  1632  	if s == "0" {
  1633  		return 0, nil
  1634  	}
  1635  	if s == "" {
  1636  		return 0, errors.New("time: invalid duration " + quote(orig))
  1637  	}
  1638  	for s != "" {
  1639  		var (
  1640  			v, f  uint64      // integers before, after decimal point
  1641  			scale float64 = 1 // value = v + f/scale
  1642  		)
  1643  
  1644  		var err error
  1645  
  1646  		// The next character must be [0-9.]
  1647  		if !(s[0] == '.' || '0' <= s[0] && s[0] <= '9') {
  1648  			return 0, errors.New("time: invalid duration " + quote(orig))
  1649  		}
  1650  		// Consume [0-9]*
  1651  		pl := len(s)
  1652  		v, s, err = leadingInt(s)
  1653  		if err != nil {
  1654  			return 0, errors.New("time: invalid duration " + quote(orig))
  1655  		}
  1656  		pre := pl != len(s) // whether we consumed anything before a period
  1657  
  1658  		// Consume (\.[0-9]*)?
  1659  		post := false
  1660  		if s != "" && s[0] == '.' {
  1661  			s = s[1:]
  1662  			pl := len(s)
  1663  			f, scale, s = leadingFraction(s)
  1664  			post = pl != len(s)
  1665  		}
  1666  		if !pre && !post {
  1667  			// no digits (e.g. ".s" or "-.s")
  1668  			return 0, errors.New("time: invalid duration " + quote(orig))
  1669  		}
  1670  
  1671  		// Consume unit.
  1672  		i := 0
  1673  		for ; i < len(s); i++ {
  1674  			c := s[i]
  1675  			if c == '.' || '0' <= c && c <= '9' {
  1676  				break
  1677  			}
  1678  		}
  1679  		if i == 0 {
  1680  			return 0, errors.New("time: missing unit in duration " + quote(orig))
  1681  		}
  1682  		u := s[:i]
  1683  		s = s[i:]
  1684  		unit, ok := unitMap[u]
  1685  		if !ok {
  1686  			return 0, errors.New("time: unknown unit " + quote(u) + " in duration " + quote(orig))
  1687  		}
  1688  		if v > 1<<63/unit {
  1689  			// overflow
  1690  			return 0, errors.New("time: invalid duration " + quote(orig))
  1691  		}
  1692  		v *= unit
  1693  		if f > 0 {
  1694  			// float64 is needed to be nanosecond accurate for fractions of hours.
  1695  			// v >= 0 && (f*unit/scale) <= 3.6e+12 (ns/h, h is the largest unit)
  1696  			v += uint64(float64(f) * (float64(unit) / scale))
  1697  			if v > 1<<63 {
  1698  				// overflow
  1699  				return 0, errors.New("time: invalid duration " + quote(orig))
  1700  			}
  1701  		}
  1702  		d += v
  1703  		if d > 1<<63 {
  1704  			return 0, errors.New("time: invalid duration " + quote(orig))
  1705  		}
  1706  	}
  1707  	if neg {
  1708  		return -Duration(d), nil
  1709  	}
  1710  	if d > 1<<63-1 {
  1711  		return 0, errors.New("time: invalid duration " + quote(orig))
  1712  	}
  1713  	return Duration(d), nil
  1714  }
  1715  

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