From: ErikPelli <erikpellizzon1@gmail.com>
Date: Sun, 14 Aug 2022 07:46:22 +0000 (+0000)
Subject: encoding/base64: optimize decodemap memory set
X-Git-Tag: go1.20rc1~1605
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=e1b62efaf33988a5153510898d37309cee78f26e;p=gostls13.git

encoding/base64: optimize decodemap memory set

The existing implementation has an execution time higher in the benchmark than this one.
This is an optimized implementation using the copy() function and a constant 256 bytes string with the values to be copied.

```
name           old time/op    new time/op    delta
NewEncoding-4     329ns ± 1%     231ns ± 1%  -29.72%  (p=0.008 n=5+5)

name           old speed      new speed      delta
NewEncoding-4   778MB/s ± 1%  1108MB/s ± 1%  +42.29%  (p=0.008 n=5+5)
```

Fixes #53211

Change-Id: I80fe62aa40623125ef81ae9164a8405eed30b71b
GitHub-Last-Rev: 55dce6f636ad29a70daa935169710c22f44ab31f
GitHub-Pull-Request: golang/go#53212
Reviewed-on: https://go-review.googlesource.com/c/go/+/410194
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Keith Randall <khr@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
---

diff --git a/src/encoding/base32/base32.go b/src/encoding/base32/base32.go
index fa6e42e26c..41d343aaac 100644
--- a/src/encoding/base32/base32.go
+++ b/src/encoding/base32/base32.go
@@ -25,8 +25,25 @@ type Encoding struct {
 }
 
 const (
-	StdPadding rune = '=' // Standard padding character
-	NoPadding  rune = -1  // No padding
+	StdPadding          rune = '=' // Standard padding character
+	NoPadding           rune = -1  // No padding
+	decodeMapInitialize      = "" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
 )
 
 const encodeStd = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
@@ -40,12 +57,10 @@ func NewEncoding(encoder string) *Encoding {
 	}
 
 	e := new(Encoding)
-	copy(e.encode[:], encoder)
 	e.padChar = StdPadding
+	copy(e.encode[:], encoder)
+	copy(e.decodeMap[:], decodeMapInitialize)
 
-	for i := 0; i < len(e.decodeMap); i++ {
-		e.decodeMap[i] = 0xFF
-	}
 	for i := 0; i < len(encoder); i++ {
 		e.decodeMap[encoder[i]] = byte(i)
 	}
diff --git a/src/encoding/base64/base64.go b/src/encoding/base64/base64.go
index 4a3e590649..0e12d90d29 100644
--- a/src/encoding/base64/base64.go
+++ b/src/encoding/base64/base64.go
@@ -28,8 +28,25 @@ type Encoding struct {
 }
 
 const (
-	StdPadding rune = '=' // Standard padding character
-	NoPadding  rune = -1  // No padding
+	StdPadding          rune = '=' // Standard padding character
+	NoPadding           rune = -1  // No padding
+	decodeMapInitialize      = "" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
 )
 
 const encodeStd = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
@@ -53,10 +70,8 @@ func NewEncoding(encoder string) *Encoding {
 	e := new(Encoding)
 	e.padChar = StdPadding
 	copy(e.encode[:], encoder)
+	copy(e.decodeMap[:], decodeMapInitialize)
 
-	for i := 0; i < len(e.decodeMap); i++ {
-		e.decodeMap[i] = 0xFF
-	}
 	for i := 0; i < len(encoder); i++ {
 		e.decodeMap[encoder[i]] = byte(i)
 	}
diff --git a/src/encoding/base64/base64_test.go b/src/encoding/base64/base64_test.go
index 57256a3846..852446dd8b 100644
--- a/src/encoding/base64/base64_test.go
+++ b/src/encoding/base64/base64_test.go
@@ -504,6 +504,16 @@ func BenchmarkDecodeString(b *testing.B) {
 	}
 }
 
+func BenchmarkNewEncoding(b *testing.B) {
+	b.SetBytes(int64(len(Encoding{}.decodeMap)))
+	for i := 0; i < b.N; i++ {
+		e := NewEncoding(encodeStd)
+		for _, v := range e.decodeMap {
+			_ = v
+		}
+	}
+}
+
 func TestDecoderRaw(t *testing.T) {
 	source := "AAAAAA"
 	want := []byte{0, 0, 0, 0}