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// 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"
"log"
"math"
"os"
)
func main() {
var buf bytes.Buffer
fmt.Fprintln(&buf, "// Code generated by mkfastlog2table.go; DO NOT EDIT.")
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 := os.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
}
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