From a72fdb11cdc1c206fe949bfd60e84fe5bbcaa301 Mon Sep 17 00:00:00 2001
From: Mateusz Poliwczak <mpoliwczak34@gmail.com>
Date: Wed, 8 May 2024 19:13:02 +0200
Subject: [PATCH 1/2] encoding/hex: don't over allocate memory in DecodeString

Change-Id: Ie9137639e2b39690f2246948d7ff58f09fc84e68
---
 src/encoding/hex/hex.go      |  8 +++-----
 src/encoding/hex/hex_test.go | 14 ++++++++++++++
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/src/encoding/hex/hex.go b/src/encoding/hex/hex.go
index 791d2bd4adfad3..ba9cc0f967f611 100644
--- a/src/encoding/hex/hex.go
+++ b/src/encoding/hex/hex.go
@@ -136,11 +136,9 @@ func EncodeToString(src []byte) string {
 // If the input is malformed, DecodeString returns
 // the bytes decoded before the error.
 func DecodeString(s string) ([]byte, error) {
-	src := []byte(s)
-	// We can use the source slice itself as the destination
-	// because the decode loop increments by one and then the 'seen' byte is not used anymore.
-	n, err := Decode(src, src)
-	return src[:n], err
+	dst := make([]byte, DecodedLen(len(s)))
+	n, err := Decode(dst, []byte(s))
+	return dst[:n], err
 }
 
 // Dump returns a string that contains a hex dump of the given data. The format
diff --git a/src/encoding/hex/hex_test.go b/src/encoding/hex/hex_test.go
index 03331eaae5afd4..47210c988cf4e2 100644
--- a/src/encoding/hex/hex_test.go
+++ b/src/encoding/hex/hex_test.go
@@ -275,6 +275,20 @@ func BenchmarkDecode(b *testing.B) {
 	}
 }
 
+func BenchmarkDecodeString(b *testing.B) {
+	for _, size := range []int{256, 1024, 4096, 16384} {
+		src := strings.Repeat("2b744faa", size/8)
+		sink = make([]byte, size/2)
+
+		b.Run(fmt.Sprintf("%v", size), func(b *testing.B) {
+			b.SetBytes(int64(size))
+			for i := 0; i < b.N; i++ {
+				sink, _ = DecodeString(src)
+			}
+		})
+	}
+}
+
 func BenchmarkDump(b *testing.B) {
 	for _, size := range []int{256, 1024, 4096, 16384} {
 		src := bytes.Repeat([]byte{2, 3, 5, 7, 9, 11, 13, 17}, size/8)

From aeedf3f6c4a2505ae9cc0ae58a94c6b2f30806fd Mon Sep 17 00:00:00 2001
From: Mateusz Poliwczak <mpoliwczak34@gmail.com>
Date: Wed, 8 May 2024 20:22:39 +0200
Subject: [PATCH 2/2] simplify

Change-Id: I82e0c6e883a89af46fff9955b72c79b295816561
---
 src/encoding/hex/hex_test.go | 2 --
 1 file changed, 2 deletions(-)

diff --git a/src/encoding/hex/hex_test.go b/src/encoding/hex/hex_test.go
index 47210c988cf4e2..f90dec5315761d 100644
--- a/src/encoding/hex/hex_test.go
+++ b/src/encoding/hex/hex_test.go
@@ -278,8 +278,6 @@ func BenchmarkDecode(b *testing.B) {
 func BenchmarkDecodeString(b *testing.B) {
 	for _, size := range []int{256, 1024, 4096, 16384} {
 		src := strings.Repeat("2b744faa", size/8)
-		sink = make([]byte, size/2)
-
 		b.Run(fmt.Sprintf("%v", size), func(b *testing.B) {
 			b.SetBytes(int64(size))
 			for i := 0; i < b.N; i++ {