From 22cfe24aca80653b0e8efdd4a1aba1df00e8e72d Mon Sep 17 00:00:00 2001 From: Agniva De Sarker Date: Sun, 13 Aug 2017 23:45:04 +0530 Subject: [PATCH] encoding/hex: save allocation in DecodeString() MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The destination slice does not need to be created at all. The source slice itself can be used as the destination because the decode loop increments by one and then the 'seen' byte is not used anymore. Therefore the decoded byte can be stored in that index of the source slice itself. This trick cannot be applied to EncodeString() because in that case, the destination slice is large than the source. And for a single byte in the source slice, two bytes in the destination slice is written. func BenchmarkDecodeString(b *testing.B) { for i := 0; i < b.N; i++ { DecodeString("0123456789abcdef") } } name old time/op new time/op delta DecodeString 71.0ns ± 6% 58.0ns ± 0% -18.28% (p=0.008 n=5+5) name old alloc/op new alloc/op delta DecodeString 16.0B ± 0% 8.0B ± 0% -50.00% (p=0.008 n=5+5) name old allocs/op new allocs/op delta DecodeString 1.00 ± 0% 1.00 ± 0% ~ (all equal) Change-Id: Id98db4e712444557a804155457a4dd8d1b8b416d Reviewed-on: https://go-review.googlesource.com/55611 Reviewed-by: Ian Lance Taylor Run-TryBot: Ian Lance Taylor TryBot-Result: Gobot Gobot --- src/encoding/hex/hex.go | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/src/encoding/hex/hex.go b/src/encoding/hex/hex.go index 2768f1bac6..18e0c09ef3 100644 --- a/src/encoding/hex/hex.go +++ b/src/encoding/hex/hex.go @@ -94,12 +94,13 @@ func EncodeToString(src []byte) string { // DecodeString returns the bytes represented by the hexadecimal string s. func DecodeString(s string) ([]byte, error) { src := []byte(s) - dst := make([]byte, DecodedLen(len(src))) - _, err := Decode(dst, src) + // 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. + len, err := Decode(src, src) if err != nil { return nil, err } - return dst, nil + return src[:len], nil } // Dump returns a string that contains a hex dump of the given data. The format -- 2.48.1