fastlog2_test.go

Documentation: runtime

     1  // Copyright 2015 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 runtime_test
     6  
     7  import (
     8  	"math"
     9  	"runtime"
    10  	"testing"
    11  )
    12  
    13  func TestFastLog2(t *testing.T) {
    14  	// Compute the euclidean distance between math.Log2 and the FastLog2
    15  	// implementation over the range of interest for heap sampling.
    16  	const randomBitCount = 26
    17  	var e float64
    18  
    19  	inc := 1
    20  	if testing.Short() {
    21  		// Check 1K total values, down from 64M.
    22  		inc = 1 << 16
    23  	}
    24  	for i := 1; i < 1<<randomBitCount; i += inc {
    25  		l, fl := math.Log2(float64(i)), runtime.Fastlog2(float64(i))
    26  		d := l - fl
    27  		e += d * d
    28  	}
    29  	e = math.Sqrt(e)
    30  
    31  	if e > 1.0 {
    32  		t.Fatalf("imprecision on fastlog2 implementation, want <=1.0, got %f", e)
    33  	}
    34  }
    35
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