From 9aed16e96dc97a68a00e6358fe05f96ce5c16b35 Mon Sep 17 00:00:00 2001 From: Ingo Oeser Date: Tue, 18 Oct 2016 18:05:43 +0200 Subject: [PATCH] regexp: avoid alloc in QuoteMeta when not quoting MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Many users quote literals in regular expressions just in case. No need to allocate then. Note: Also added benchmarks for quoting and not quoting. name old time/op new time/op delta QuoteMetaAll-4 629ns ± 6% 654ns ± 5% +4.01% (p=0.001 n=20+19) QuoteMetaNone-4 1.02µs ± 6% 0.20µs ± 0% -80.73% (p=0.000 n=18+20) name old speed new speed delta QuoteMetaAll-4 22.3MB/s ± 6% 21.4MB/s ± 5% -3.94% (p=0.001 n=20+19) QuoteMetaNone-4 25.3MB/s ± 3% 131.5MB/s ± 0% +419.28% (p=0.000 n=17+19) name old alloc/op new alloc/op delta QuoteMetaAll-4 64.0B ± 0% 64.0B ± 0% ~ (all samples are equal) QuoteMetaNone-4 96.0B ± 0% 0.0B ±NaN% -100.00% (p=0.000 n=20+20) name old allocs/op new allocs/op delta QuoteMetaAll-4 2.00 ± 0% 2.00 ± 0% ~ (all samples are equal) QuoteMetaNone-4 2.00 ± 0% 0.00 ±NaN% -100.00% (p=0.000 n=20+20) Change-Id: I38d50f463cde463115d22534f8eb849e54d899af Reviewed-on: https://go-review.googlesource.com/31395 Reviewed-by: Russ Cox Reviewed-by: Austin Clements Run-TryBot: Brad Fitzpatrick TryBot-Result: Gobot Gobot --- src/regexp/all_test.go | 20 ++++++++++++++++++++ src/regexp/regexp.go | 21 ++++++++++++++++----- 2 files changed, 36 insertions(+), 5 deletions(-) diff --git a/src/regexp/all_test.go b/src/regexp/all_test.go index 31843d41f1..beb46e7099 100644 --- a/src/regexp/all_test.go +++ b/src/regexp/all_test.go @@ -818,3 +818,23 @@ func BenchmarkMatchParallelCopied(b *testing.B) { } }) } + +var sink string + +func BenchmarkQuoteMetaAll(b *testing.B) { + s := string(specialBytes) + b.SetBytes(int64(len(s))) + b.ResetTimer() + for i := 0; i < b.N; i++ { + sink = QuoteMeta(s) + } +} + +func BenchmarkQuoteMetaNone(b *testing.B) { + s := "abcdefghijklmnopqrstuvwxyz" + b.SetBytes(int64(len(s))) + b.ResetTimer() + for i := 0; i < b.N; i++ { + sink = QuoteMeta(s) + } +} diff --git a/src/regexp/regexp.go b/src/regexp/regexp.go index 87a3e88d9a..01093d4bd0 100644 --- a/src/regexp/regexp.go +++ b/src/regexp/regexp.go @@ -600,11 +600,22 @@ func special(b byte) bool { // inside the argument text; the returned string is a regular expression matching // the literal text. For example, QuoteMeta(`[foo]`) returns `\[foo\]`. func QuoteMeta(s string) string { - b := make([]byte, 2*len(s)) - // A byte loop is correct because all metacharacters are ASCII. - j := 0 - for i := 0; i < len(s); i++ { + var i int + for i = 0; i < len(s); i++ { + if special(s[i]) { + break + } + } + // No meta characters found, so return original string. + if i >= len(s) { + return s + } + + b := make([]byte, 2*len(s)-i) + copy(b, s[:i]) + j := i + for ; i < len(s); i++ { if special(s[i]) { b[j] = '\\' j++ @@ -612,7 +623,7 @@ func QuoteMeta(s string) string { b[j] = s[i] j++ } - return string(b[0:j]) + return string(b[:j]) } // The number of capture values in the program may correspond