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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-16 19:23:18 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-16 19:23:18 +0000
commit43a123c1ae6613b3efeed291fa552ecd909d3acf (patch)
treefd92518b7024bc74031f78a1cf9e454b65e73665 /src/math/bits/make_tables.go
parentInitial commit. (diff)
downloadgolang-1.20-43a123c1ae6613b3efeed291fa552ecd909d3acf.tar.xz
golang-1.20-43a123c1ae6613b3efeed291fa552ecd909d3acf.zip
Adding upstream version 1.20.14.upstream/1.20.14upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r--src/math/bits/make_tables.go92
1 files changed, 92 insertions, 0 deletions
diff --git a/src/math/bits/make_tables.go b/src/math/bits/make_tables.go
new file mode 100644
index 0000000..867025e
--- /dev/null
+++ b/src/math/bits/make_tables.go
@@ -0,0 +1,92 @@
+// Copyright 2017 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.
+
+//go:build ignore
+// +build ignore
+
+// This program generates bits_tables.go.
+
+package main
+
+import (
+ "bytes"
+ "fmt"
+ "go/format"
+ "io"
+ "log"
+ "os"
+)
+
+var header = []byte(`// Copyright 2017 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.
+
+// Code generated by go run make_tables.go. DO NOT EDIT.
+
+package bits
+
+`)
+
+func main() {
+ buf := bytes.NewBuffer(header)
+
+ gen(buf, "ntz8tab", ntz8)
+ gen(buf, "pop8tab", pop8)
+ gen(buf, "rev8tab", rev8)
+ gen(buf, "len8tab", len8)
+
+ out, err := format.Source(buf.Bytes())
+ if err != nil {
+ log.Fatal(err)
+ }
+
+ err = os.WriteFile("bits_tables.go", out, 0666)
+ if err != nil {
+ log.Fatal(err)
+ }
+}
+
+func gen(w io.Writer, name string, f func(uint8) uint8) {
+ // Use a const string to allow the compiler to constant-evaluate lookups at constant index.
+ fmt.Fprintf(w, "const %s = \"\"+\n\"", name)
+ for i := 0; i < 256; i++ {
+ fmt.Fprintf(w, "\\x%02x", f(uint8(i)))
+ if i%16 == 15 && i != 255 {
+ fmt.Fprint(w, "\"+\n\"")
+ }
+ }
+ fmt.Fprint(w, "\"\n\n")
+}
+
+func ntz8(x uint8) (n uint8) {
+ for x&1 == 0 && n < 8 {
+ x >>= 1
+ n++
+ }
+ return
+}
+
+func pop8(x uint8) (n uint8) {
+ for x != 0 {
+ x &= x - 1
+ n++
+ }
+ return
+}
+
+func rev8(x uint8) (r uint8) {
+ for i := 8; i > 0; i-- {
+ r = r<<1 | x&1
+ x >>= 1
+ }
+ return
+}
+
+func len8(x uint8) (n uint8) {
+ for x != 0 {
+ x >>= 1
+ n++
+ }
+ return
+}