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