1 files changed, 52 insertions, 0 deletions
diff --git a/src/runtime/mkfastlog2table.go b/src/runtime/mkfastlog2table.go
new file mode 100644
index 0000000..d650292
--- /dev/null
+++ b/src/runtime/mkfastlog2table.go
@@ -0,0 +1,52 @@
+// 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
+}