libgo/go/runtime/fastlog2_test.go

   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 // +build ignore
   6
   7 package runtime_test
   8
   9 import (
  10         "math"
  11         "runtime"
  12         "testing"
  13 )
  14
  15 func TestFastLog2(t *testing.T) {
  16         // Compute the euclidean distance between math.Log2 and the FastLog2
  17         // implementation over the range of interest for heap sampling.
  18         const randomBitCount = 26
  19         var e float64
  20
  21         inc := 1
  22         if testing.Short() {
  23                 // Check 1K total values, down from 64M.
  24                 inc = 1 << 16
  25         }
  26         for i := 1; i < 1<<randomBitCount; i += inc {
  27                 l, fl := math.Log2(float64(i)), runtime.Fastlog2(float64(i))
  28                 d := l - fl
  29                 e += d * d
  30         }
  31         e = math.Sqrt(e)
  32
  33         if e > 1.0 {
  34                 t.Fatalf("imprecision on fastlog2 implementation, want <=1.0, got %f", e)
  35         }
  36 }