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 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 }