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Text file src/vendor/golang.org/x/crypto/internal/poly1305/sum_s390x.s

Documentation: vendor/golang.org/x/crypto/internal/poly1305

     1// Copyright 2018 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//go:build gc && !purego
     6
     7#include "textflag.h"
     8
     9// This implementation of Poly1305 uses the vector facility (vx)
    10// to process up to 2 blocks (32 bytes) per iteration using an
    11// algorithm based on the one described in:
    12//
    13// NEON crypto, Daniel J. Bernstein & Peter Schwabe
    14// https://cryptojedi.org/papers/neoncrypto-20120320.pdf
    15//
    16// This algorithm uses 5 26-bit limbs to represent a 130-bit
    17// value. These limbs are, for the most part, zero extended and
    18// placed into 64-bit vector register elements. Each vector
    19// register is 128-bits wide and so holds 2 of these elements.
    20// Using 26-bit limbs allows us plenty of headroom to accommodate
    21// accumulations before and after multiplication without
    22// overflowing either 32-bits (before multiplication) or 64-bits
    23// (after multiplication).
    24//
    25// In order to parallelise the operations required to calculate
    26// the sum we use two separate accumulators and then sum those
    27// in an extra final step. For compatibility with the generic
    28// implementation we perform this summation at the end of every
    29// updateVX call.
    30//
    31// To use two accumulators we must multiply the message blocks
    32// by r² rather than r. Only the final message block should be
    33// multiplied by r.
    34//
    35// Example:
    36//
    37// We want to calculate the sum (h) for a 64 byte message (m):
    38//
    39//   h = m[0:16]r⁴ + m[16:32]r³ + m[32:48]r² + m[48:64]r
    40//
    41// To do this we split the calculation into the even indices
    42// and odd indices of the message. These form our SIMD 'lanes':
    43//
    44//   h = m[ 0:16]r⁴ + m[32:48]r² +   <- lane 0
    45//       m[16:32]r³ + m[48:64]r      <- lane 1
    46//
    47// To calculate this iteratively we refactor so that both lanes
    48// are written in terms of r² and r:
    49//
    50//   h = (m[ 0:16]r² + m[32:48])r² + <- lane 0
    51//       (m[16:32]r² + m[48:64])r    <- lane 1
    52//                ^             ^
    53//                |             coefficients for second iteration
    54//                coefficients for first iteration
    55//
    56// So in this case we would have two iterations. In the first
    57// both lanes are multiplied by r². In the second only the
    58// first lane is multiplied by r² and the second lane is
    59// instead multiplied by r. This gives use the odd and even
    60// powers of r that we need from the original equation.
    61//
    62// Notation:
    63//
    64//   h - accumulator
    65//   r - key
    66//   m - message
    67//
    68//   [a, b]       - SIMD register holding two 64-bit values
    69//   [a, b, c, d] - SIMD register holding four 32-bit values
    70//   xᵢ[n]        - limb n of variable x with bit width i
    71//
    72// Limbs are expressed in little endian order, so for 26-bit
    73// limbs x₂₆[4] will be the most significant limb and x₂₆[0]
    74// will be the least significant limb.
    75
    76// masking constants
    77#define MOD24 V0 // [0x0000000000ffffff, 0x0000000000ffffff] - mask low 24-bits
    78#define MOD26 V1 // [0x0000000003ffffff, 0x0000000003ffffff] - mask low 26-bits
    79
    80// expansion constants (see EXPAND macro)
    81#define EX0 V2
    82#define EX1 V3
    83#define EX2 V4
    84
    85// key (r², r or 1 depending on context)
    86#define R_0 V5
    87#define R_1 V6
    88#define R_2 V7
    89#define R_3 V8
    90#define R_4 V9
    91
    92// precalculated coefficients (5r², 5r or 0 depending on context)
    93#define R5_1 V10
    94#define R5_2 V11
    95#define R5_3 V12
    96#define R5_4 V13
    97
    98// message block (m)
    99#define M_0 V14
   100#define M_1 V15
   101#define M_2 V16
   102#define M_3 V17
   103#define M_4 V18
   104
   105// accumulator (h)
   106#define H_0 V19
   107#define H_1 V20
   108#define H_2 V21
   109#define H_3 V22
   110#define H_4 V23
   111
   112// temporary registers (for short-lived values)
   113#define T_0 V24
   114#define T_1 V25
   115#define T_2 V26
   116#define T_3 V27
   117#define T_4 V28
   118
   119GLOBL ·constants<>(SB), RODATA, $0x30
   120// EX0
   121DATA ·constants<>+0x00(SB)/8, $0x0006050403020100
   122DATA ·constants<>+0x08(SB)/8, $0x1016151413121110
   123// EX1
   124DATA ·constants<>+0x10(SB)/8, $0x060c0b0a09080706
   125DATA ·constants<>+0x18(SB)/8, $0x161c1b1a19181716
   126// EX2
   127DATA ·constants<>+0x20(SB)/8, $0x0d0d0d0d0d0f0e0d
   128DATA ·constants<>+0x28(SB)/8, $0x1d1d1d1d1d1f1e1d
   129
   130// MULTIPLY multiplies each lane of f and g, partially reduced
   131// modulo 2¹³⁰ - 5. The result, h, consists of partial products
   132// in each lane that need to be reduced further to produce the
   133// final result.
   134//
   135//   h₁₃₀ = (f₁₃₀g₁₃₀) % 2¹³⁰ + (5f₁₃₀g₁₃₀) / 2¹³⁰
   136//
   137// Note that the multiplication by 5 of the high bits is
   138// achieved by precalculating the multiplication of four of the
   139// g coefficients by 5. These are g51-g54.
   140#define MULTIPLY(f0, f1, f2, f3, f4, g0, g1, g2, g3, g4, g51, g52, g53, g54, h0, h1, h2, h3, h4) \
   141	VMLOF  f0, g0, h0        \
   142	VMLOF  f0, g3, h3        \
   143	VMLOF  f0, g1, h1        \
   144	VMLOF  f0, g4, h4        \
   145	VMLOF  f0, g2, h2        \
   146	VMLOF  f1, g54, T_0      \
   147	VMLOF  f1, g2, T_3       \
   148	VMLOF  f1, g0, T_1       \
   149	VMLOF  f1, g3, T_4       \
   150	VMLOF  f1, g1, T_2       \
   151	VMALOF f2, g53, h0, h0   \
   152	VMALOF f2, g1, h3, h3    \
   153	VMALOF f2, g54, h1, h1   \
   154	VMALOF f2, g2, h4, h4    \
   155	VMALOF f2, g0, h2, h2    \
   156	VMALOF f3, g52, T_0, T_0 \
   157	VMALOF f3, g0, T_3, T_3  \
   158	VMALOF f3, g53, T_1, T_1 \
   159	VMALOF f3, g1, T_4, T_4  \
   160	VMALOF f3, g54, T_2, T_2 \
   161	VMALOF f4, g51, h0, h0   \
   162	VMALOF f4, g54, h3, h3   \
   163	VMALOF f4, g52, h1, h1   \
   164	VMALOF f4, g0, h4, h4    \
   165	VMALOF f4, g53, h2, h2   \
   166	VAG    T_0, h0, h0       \
   167	VAG    T_3, h3, h3       \
   168	VAG    T_1, h1, h1       \
   169	VAG    T_4, h4, h4       \
   170	VAG    T_2, h2, h2
   171
   172// REDUCE performs the following carry operations in four
   173// stages, as specified in Bernstein & Schwabe:
   174//
   175//   1: h₂₆[0]->h₂₆[1] h₂₆[3]->h₂₆[4]
   176//   2: h₂₆[1]->h₂₆[2] h₂₆[4]->h₂₆[0]
   177//   3: h₂₆[0]->h₂₆[1] h₂₆[2]->h₂₆[3]
   178//   4: h₂₆[3]->h₂₆[4]
   179//
   180// The result is that all of the limbs are limited to 26-bits
   181// except for h₂₆[1] and h₂₆[4] which are limited to 27-bits.
   182//
   183// Note that although each limb is aligned at 26-bit intervals
   184// they may contain values that exceed 2²⁶ - 1, hence the need
   185// to carry the excess bits in each limb.
   186#define REDUCE(h0, h1, h2, h3, h4) \
   187	VESRLG $26, h0, T_0  \
   188	VESRLG $26, h3, T_1  \
   189	VN     MOD26, h0, h0 \
   190	VN     MOD26, h3, h3 \
   191	VAG    T_0, h1, h1   \
   192	VAG    T_1, h4, h4   \
   193	VESRLG $26, h1, T_2  \
   194	VESRLG $26, h4, T_3  \
   195	VN     MOD26, h1, h1 \
   196	VN     MOD26, h4, h4 \
   197	VESLG  $2, T_3, T_4  \
   198	VAG    T_3, T_4, T_4 \
   199	VAG    T_2, h2, h2   \
   200	VAG    T_4, h0, h0   \
   201	VESRLG $26, h2, T_0  \
   202	VESRLG $26, h0, T_1  \
   203	VN     MOD26, h2, h2 \
   204	VN     MOD26, h0, h0 \
   205	VAG    T_0, h3, h3   \
   206	VAG    T_1, h1, h1   \
   207	VESRLG $26, h3, T_2  \
   208	VN     MOD26, h3, h3 \
   209	VAG    T_2, h4, h4
   210
   211// EXPAND splits the 128-bit little-endian values in0 and in1
   212// into 26-bit big-endian limbs and places the results into
   213// the first and second lane of d₂₆[0:4] respectively.
   214//
   215// The EX0, EX1 and EX2 constants are arrays of byte indices
   216// for permutation. The permutation both reverses the bytes
   217// in the input and ensures the bytes are copied into the
   218// destination limb ready to be shifted into their final
   219// position.
   220#define EXPAND(in0, in1, d0, d1, d2, d3, d4) \
   221	VPERM  in0, in1, EX0, d0 \
   222	VPERM  in0, in1, EX1, d2 \
   223	VPERM  in0, in1, EX2, d4 \
   224	VESRLG $26, d0, d1       \
   225	VESRLG $30, d2, d3       \
   226	VESRLG $4, d2, d2        \
   227	VN     MOD26, d0, d0     \ // [in0₂₆[0], in1₂₆[0]]
   228	VN     MOD26, d3, d3     \ // [in0₂₆[3], in1₂₆[3]]
   229	VN     MOD26, d1, d1     \ // [in0₂₆[1], in1₂₆[1]]
   230	VN     MOD24, d4, d4     \ // [in0₂₆[4], in1₂₆[4]]
   231	VN     MOD26, d2, d2     // [in0₂₆[2], in1₂₆[2]]
   232
   233// func updateVX(state *macState, msg []byte)
   234TEXT ·updateVX(SB), NOSPLIT, $0
   235	MOVD state+0(FP), R1
   236	LMG  msg+8(FP), R2, R3 // R2=msg_base, R3=msg_len
   237
   238	// load EX0, EX1 and EX2
   239	MOVD $·constants<>(SB), R5
   240	VLM  (R5), EX0, EX2
   241
   242	// generate masks
   243	VGMG $(64-24), $63, MOD24 // [0x00ffffff, 0x00ffffff]
   244	VGMG $(64-26), $63, MOD26 // [0x03ffffff, 0x03ffffff]
   245
   246	// load h (accumulator) and r (key) from state
   247	VZERO T_1               // [0, 0]
   248	VL    0(R1), T_0        // [h₆₄[0], h₆₄[1]]
   249	VLEG  $0, 16(R1), T_1   // [h₆₄[2], 0]
   250	VL    24(R1), T_2       // [r₆₄[0], r₆₄[1]]
   251	VPDI  $0, T_0, T_2, T_3 // [h₆₄[0], r₆₄[0]]
   252	VPDI  $5, T_0, T_2, T_4 // [h₆₄[1], r₆₄[1]]
   253
   254	// unpack h and r into 26-bit limbs
   255	// note: h₆₄[2] may have the low 3 bits set, so h₂₆[4] is a 27-bit value
   256	VN     MOD26, T_3, H_0            // [h₂₆[0], r₂₆[0]]
   257	VZERO  H_1                        // [0, 0]
   258	VZERO  H_3                        // [0, 0]
   259	VGMG   $(64-12-14), $(63-12), T_0 // [0x03fff000, 0x03fff000] - 26-bit mask with low 12 bits masked out
   260	VESLG  $24, T_1, T_1              // [h₆₄[2]<<24, 0]
   261	VERIMG $-26&63, T_3, MOD26, H_1   // [h₂₆[1], r₂₆[1]]
   262	VESRLG $+52&63, T_3, H_2          // [h₂₆[2], r₂₆[2]] - low 12 bits only
   263	VERIMG $-14&63, T_4, MOD26, H_3   // [h₂₆[1], r₂₆[1]]
   264	VESRLG $40, T_4, H_4              // [h₂₆[4], r₂₆[4]] - low 24 bits only
   265	VERIMG $+12&63, T_4, T_0, H_2     // [h₂₆[2], r₂₆[2]] - complete
   266	VO     T_1, H_4, H_4              // [h₂₆[4], r₂₆[4]] - complete
   267
   268	// replicate r across all 4 vector elements
   269	VREPF $3, H_0, R_0 // [r₂₆[0], r₂₆[0], r₂₆[0], r₂₆[0]]
   270	VREPF $3, H_1, R_1 // [r₂₆[1], r₂₆[1], r₂₆[1], r₂₆[1]]
   271	VREPF $3, H_2, R_2 // [r₂₆[2], r₂₆[2], r₂₆[2], r₂₆[2]]
   272	VREPF $3, H_3, R_3 // [r₂₆[3], r₂₆[3], r₂₆[3], r₂₆[3]]
   273	VREPF $3, H_4, R_4 // [r₂₆[4], r₂₆[4], r₂₆[4], r₂₆[4]]
   274
   275	// zero out lane 1 of h
   276	VLEIG $1, $0, H_0 // [h₂₆[0], 0]
   277	VLEIG $1, $0, H_1 // [h₂₆[1], 0]
   278	VLEIG $1, $0, H_2 // [h₂₆[2], 0]
   279	VLEIG $1, $0, H_3 // [h₂₆[3], 0]
   280	VLEIG $1, $0, H_4 // [h₂₆[4], 0]
   281
   282	// calculate 5r (ignore least significant limb)
   283	VREPIF $5, T_0
   284	VMLF   T_0, R_1, R5_1 // [5r₂₆[1], 5r₂₆[1], 5r₂₆[1], 5r₂₆[1]]
   285	VMLF   T_0, R_2, R5_2 // [5r₂₆[2], 5r₂₆[2], 5r₂₆[2], 5r₂₆[2]]
   286	VMLF   T_0, R_3, R5_3 // [5r₂₆[3], 5r₂₆[3], 5r₂₆[3], 5r₂₆[3]]
   287	VMLF   T_0, R_4, R5_4 // [5r₂₆[4], 5r₂₆[4], 5r₂₆[4], 5r₂₆[4]]
   288
   289	// skip r² calculation if we are only calculating one block
   290	CMPBLE R3, $16, skip
   291
   292	// calculate r²
   293	MULTIPLY(R_0, R_1, R_2, R_3, R_4, R_0, R_1, R_2, R_3, R_4, R5_1, R5_2, R5_3, R5_4, M_0, M_1, M_2, M_3, M_4)
   294	REDUCE(M_0, M_1, M_2, M_3, M_4)
   295	VGBM   $0x0f0f, T_0
   296	VERIMG $0, M_0, T_0, R_0 // [r₂₆[0], r²₂₆[0], r₂₆[0], r²₂₆[0]]
   297	VERIMG $0, M_1, T_0, R_1 // [r₂₆[1], r²₂₆[1], r₂₆[1], r²₂₆[1]]
   298	VERIMG $0, M_2, T_0, R_2 // [r₂₆[2], r²₂₆[2], r₂₆[2], r²₂₆[2]]
   299	VERIMG $0, M_3, T_0, R_3 // [r₂₆[3], r²₂₆[3], r₂₆[3], r²₂₆[3]]
   300	VERIMG $0, M_4, T_0, R_4 // [r₂₆[4], r²₂₆[4], r₂₆[4], r²₂₆[4]]
   301
   302	// calculate 5r² (ignore least significant limb)
   303	VREPIF $5, T_0
   304	VMLF   T_0, R_1, R5_1 // [5r₂₆[1], 5r²₂₆[1], 5r₂₆[1], 5r²₂₆[1]]
   305	VMLF   T_0, R_2, R5_2 // [5r₂₆[2], 5r²₂₆[2], 5r₂₆[2], 5r²₂₆[2]]
   306	VMLF   T_0, R_3, R5_3 // [5r₂₆[3], 5r²₂₆[3], 5r₂₆[3], 5r²₂₆[3]]
   307	VMLF   T_0, R_4, R5_4 // [5r₂₆[4], 5r²₂₆[4], 5r₂₆[4], 5r²₂₆[4]]
   308
   309loop:
   310	CMPBLE R3, $32, b2 // 2 or fewer blocks remaining, need to change key coefficients
   311
   312	// load next 2 blocks from message
   313	VLM (R2), T_0, T_1
   314
   315	// update message slice
   316	SUB  $32, R3
   317	MOVD $32(R2), R2
   318
   319	// unpack message blocks into 26-bit big-endian limbs
   320	EXPAND(T_0, T_1, M_0, M_1, M_2, M_3, M_4)
   321
   322	// add 2¹²⁸ to each message block value
   323	VLEIB $4, $1, M_4
   324	VLEIB $12, $1, M_4
   325
   326multiply:
   327	// accumulate the incoming message
   328	VAG H_0, M_0, M_0
   329	VAG H_3, M_3, M_3
   330	VAG H_1, M_1, M_1
   331	VAG H_4, M_4, M_4
   332	VAG H_2, M_2, M_2
   333
   334	// multiply the accumulator by the key coefficient
   335	MULTIPLY(M_0, M_1, M_2, M_3, M_4, R_0, R_1, R_2, R_3, R_4, R5_1, R5_2, R5_3, R5_4, H_0, H_1, H_2, H_3, H_4)
   336
   337	// carry and partially reduce the partial products
   338	REDUCE(H_0, H_1, H_2, H_3, H_4)
   339
   340	CMPBNE R3, $0, loop
   341
   342finish:
   343	// sum lane 0 and lane 1 and put the result in lane 1
   344	VZERO  T_0
   345	VSUMQG H_0, T_0, H_0
   346	VSUMQG H_3, T_0, H_3
   347	VSUMQG H_1, T_0, H_1
   348	VSUMQG H_4, T_0, H_4
   349	VSUMQG H_2, T_0, H_2
   350
   351	// reduce again after summation
   352	// TODO(mundaym): there might be a more efficient way to do this
   353	// now that we only have 1 active lane. For example, we could
   354	// simultaneously pack the values as we reduce them.
   355	REDUCE(H_0, H_1, H_2, H_3, H_4)
   356
   357	// carry h[1] through to h[4] so that only h[4] can exceed 2²⁶ - 1
   358	// TODO(mundaym): in testing this final carry was unnecessary.
   359	// Needs a proof before it can be removed though.
   360	VESRLG $26, H_1, T_1
   361	VN     MOD26, H_1, H_1
   362	VAQ    T_1, H_2, H_2
   363	VESRLG $26, H_2, T_2
   364	VN     MOD26, H_2, H_2
   365	VAQ    T_2, H_3, H_3
   366	VESRLG $26, H_3, T_3
   367	VN     MOD26, H_3, H_3
   368	VAQ    T_3, H_4, H_4
   369
   370	// h is now < 2(2¹³⁰ - 5)
   371	// Pack each lane in h₂₆[0:4] into h₁₂₈[0:1].
   372	VESLG $26, H_1, H_1
   373	VESLG $26, H_3, H_3
   374	VO    H_0, H_1, H_0
   375	VO    H_2, H_3, H_2
   376	VESLG $4, H_2, H_2
   377	VLEIB $7, $48, H_1
   378	VSLB  H_1, H_2, H_2
   379	VO    H_0, H_2, H_0
   380	VLEIB $7, $104, H_1
   381	VSLB  H_1, H_4, H_3
   382	VO    H_3, H_0, H_0
   383	VLEIB $7, $24, H_1
   384	VSRLB H_1, H_4, H_1
   385
   386	// update state
   387	VSTEG $1, H_0, 0(R1)
   388	VSTEG $0, H_0, 8(R1)
   389	VSTEG $1, H_1, 16(R1)
   390	RET
   391
   392b2:  // 2 or fewer blocks remaining
   393	CMPBLE R3, $16, b1
   394
   395	// Load the 2 remaining blocks (17-32 bytes remaining).
   396	MOVD $-17(R3), R0    // index of final byte to load modulo 16
   397	VL   (R2), T_0       // load full 16 byte block
   398	VLL  R0, 16(R2), T_1 // load final (possibly partial) block and pad with zeros to 16 bytes
   399
   400	// The Poly1305 algorithm requires that a 1 bit be appended to
   401	// each message block. If the final block is less than 16 bytes
   402	// long then it is easiest to insert the 1 before the message
   403	// block is split into 26-bit limbs. If, on the other hand, the
   404	// final message block is 16 bytes long then we append the 1 bit
   405	// after expansion as normal.
   406	MOVBZ  $1, R0
   407	MOVD   $-16(R3), R3   // index of byte in last block to insert 1 at (could be 16)
   408	CMPBEQ R3, $16, 2(PC) // skip the insertion if the final block is 16 bytes long
   409	VLVGB  R3, R0, T_1    // insert 1 into the byte at index R3
   410
   411	// Split both blocks into 26-bit limbs in the appropriate lanes.
   412	EXPAND(T_0, T_1, M_0, M_1, M_2, M_3, M_4)
   413
   414	// Append a 1 byte to the end of the second to last block.
   415	VLEIB $4, $1, M_4
   416
   417	// Append a 1 byte to the end of the last block only if it is a
   418	// full 16 byte block.
   419	CMPBNE R3, $16, 2(PC)
   420	VLEIB  $12, $1, M_4
   421
   422	// Finally, set up the coefficients for the final multiplication.
   423	// We have previously saved r and 5r in the 32-bit even indexes
   424	// of the R_[0-4] and R5_[1-4] coefficient registers.
   425	//
   426	// We want lane 0 to be multiplied by r² so that can be kept the
   427	// same. We want lane 1 to be multiplied by r so we need to move
   428	// the saved r value into the 32-bit odd index in lane 1 by
   429	// rotating the 64-bit lane by 32.
   430	VGBM   $0x00ff, T_0         // [0, 0xffffffffffffffff] - mask lane 1 only
   431	VERIMG $32, R_0, T_0, R_0   // [_,  r²₂₆[0], _,  r₂₆[0]]
   432	VERIMG $32, R_1, T_0, R_1   // [_,  r²₂₆[1], _,  r₂₆[1]]
   433	VERIMG $32, R_2, T_0, R_2   // [_,  r²₂₆[2], _,  r₂₆[2]]
   434	VERIMG $32, R_3, T_0, R_3   // [_,  r²₂₆[3], _,  r₂₆[3]]
   435	VERIMG $32, R_4, T_0, R_4   // [_,  r²₂₆[4], _,  r₂₆[4]]
   436	VERIMG $32, R5_1, T_0, R5_1 // [_, 5r²₂₆[1], _, 5r₂₆[1]]
   437	VERIMG $32, R5_2, T_0, R5_2 // [_, 5r²₂₆[2], _, 5r₂₆[2]]
   438	VERIMG $32, R5_3, T_0, R5_3 // [_, 5r²₂₆[3], _, 5r₂₆[3]]
   439	VERIMG $32, R5_4, T_0, R5_4 // [_, 5r²₂₆[4], _, 5r₂₆[4]]
   440
   441	MOVD $0, R3
   442	BR   multiply
   443
   444skip:
   445	CMPBEQ R3, $0, finish
   446
   447b1:  // 1 block remaining
   448
   449	// Load the final block (1-16 bytes). This will be placed into
   450	// lane 0.
   451	MOVD $-1(R3), R0
   452	VLL  R0, (R2), T_0 // pad to 16 bytes with zeros
   453
   454	// The Poly1305 algorithm requires that a 1 bit be appended to
   455	// each message block. If the final block is less than 16 bytes
   456	// long then it is easiest to insert the 1 before the message
   457	// block is split into 26-bit limbs. If, on the other hand, the
   458	// final message block is 16 bytes long then we append the 1 bit
   459	// after expansion as normal.
   460	MOVBZ  $1, R0
   461	CMPBEQ R3, $16, 2(PC)
   462	VLVGB  R3, R0, T_0
   463
   464	// Set the message block in lane 1 to the value 0 so that it
   465	// can be accumulated without affecting the final result.
   466	VZERO T_1
   467
   468	// Split the final message block into 26-bit limbs in lane 0.
   469	// Lane 1 will be contain 0.
   470	EXPAND(T_0, T_1, M_0, M_1, M_2, M_3, M_4)
   471
   472	// Append a 1 byte to the end of the last block only if it is a
   473	// full 16 byte block.
   474	CMPBNE R3, $16, 2(PC)
   475	VLEIB  $4, $1, M_4
   476
   477	// We have previously saved r and 5r in the 32-bit even indexes
   478	// of the R_[0-4] and R5_[1-4] coefficient registers.
   479	//
   480	// We want lane 0 to be multiplied by r so we need to move the
   481	// saved r value into the 32-bit odd index in lane 0. We want
   482	// lane 1 to be set to the value 1. This makes multiplication
   483	// a no-op. We do this by setting lane 1 in every register to 0
   484	// and then just setting the 32-bit index 3 in R_0 to 1.
   485	VZERO T_0
   486	MOVD  $0, R0
   487	MOVD  $0x10111213, R12
   488	VLVGP R12, R0, T_1         // [_, 0x10111213, _, 0x00000000]
   489	VPERM T_0, R_0, T_1, R_0   // [_,  r₂₆[0], _, 0]
   490	VPERM T_0, R_1, T_1, R_1   // [_,  r₂₆[1], _, 0]
   491	VPERM T_0, R_2, T_1, R_2   // [_,  r₂₆[2], _, 0]
   492	VPERM T_0, R_3, T_1, R_3   // [_,  r₂₆[3], _, 0]
   493	VPERM T_0, R_4, T_1, R_4   // [_,  r₂₆[4], _, 0]
   494	VPERM T_0, R5_1, T_1, R5_1 // [_, 5r₂₆[1], _, 0]
   495	VPERM T_0, R5_2, T_1, R5_2 // [_, 5r₂₆[2], _, 0]
   496	VPERM T_0, R5_3, T_1, R5_3 // [_, 5r₂₆[3], _, 0]
   497	VPERM T_0, R5_4, T_1, R5_4 // [_, 5r₂₆[4], _, 0]
   498
   499	// Set the value of lane 1 to be 1.
   500	VLEIF $3, $1, R_0 // [_,  r₂₆[0], _, 1]
   501
   502	MOVD $0, R3
   503	BR   multiply

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