mirror of
https://github.com/golang/go
synced 2024-11-19 22:54:39 -07:00
53 lines
1.3 KiB
Go
53 lines
1.3 KiB
Go
|
// Copyright 2015 The Go Authors. All rights reserved.
|
||
|
|
// Use of this source code is governed by a BSD-style
|
||
|
|
// license that can be found in the LICENSE file.
|
||
|
|
|
||
|
|
// +build ignore
|
||
|
|
|
||
|
|
// fastlog2Table contains log2 approximations for 5 binary digits.
|
||
|
|
// This is used to implement fastlog2, which is used for heap sampling.
|
||
|
|
|
||
|
|
package main
|
||
|
|
|
||
|
|
import (
|
||
|
|
"bytes"
|
||
|
|
"fmt"
|
||
|
|
"io/ioutil"
|
||
|
|
"log"
|
||
|
|
"math"
|
||
|
|
)
|
||
|
|
|
||
|
|
func main() {
|
||
|
|
var buf bytes.Buffer
|
||
|
|
|
||
|
|
fmt.Fprintln(&buf, "// AUTO-GENERATED by mkfastlog2table.go")
|
||
|
|
fmt.Fprintln(&buf, "// Run go generate from src/runtime to update.")
|
||
|
|
fmt.Fprintln(&buf, "// See mkfastlog2table.go for comments.")
|
||
|
|
fmt.Fprintln(&buf)
|
||
|
|
fmt.Fprintln(&buf, "package runtime")
|
||
|
|
fmt.Fprintln(&buf)
|
||
|
|
fmt.Fprintln(&buf, "const fastlogNumBits =", fastlogNumBits)
|
||
|
|
fmt.Fprintln(&buf)
|
||
|
|
|
||
|
|
fmt.Fprintln(&buf, "var fastlog2Table = [1<<fastlogNumBits + 1]float64{")
|
||
|
|
table := computeTable()
|
||
|
|
for _, t := range table {
|
||
|
|
fmt.Fprintf(&buf, "\t%v,\n", t)
|
||
|
|
}
|
||
|
|
fmt.Fprintln(&buf, "}")
|
||
|
|
|
||
|
|
if err := ioutil.WriteFile("fastlog2table.go", buf.Bytes(), 0644); err != nil {
|
||
|
|
log.Fatalln(err)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
const fastlogNumBits = 5
|
||
|
|
|
||
|
|
func computeTable() []float64 {
|
||
|
|
fastlog2Table := make([]float64, 1<<fastlogNumBits+1)
|
||
|
|
for i := 0; i <= (1 << fastlogNumBits); i++ {
|
||
|
|
fastlog2Table[i] = math.Log2(1.0 + float64(i)/(1<<fastlogNumBits))
|
||
|
|
}
|
||
|
|
return fastlog2Table
|
||
|
|
}
|