bytes, strings: micro-optimize EqualFold

The first loop leaves the lengths of the two arguments unchanged.

Take advantage of this invariant in the loop's condition. Here are some
benchmark results (no change to allocations):

goos: darwin
goarch: amd64
pkg: strings
cpu: Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz
                          │     old     │                new                 │
                          │   sec/op    │   sec/op     vs base               │
EqualFold/Tests-8           240.0n ± 4%   245.1n ± 5%       ~ (p=0.516 n=20)
EqualFold/ASCII-8           11.50n ± 1%   11.04n ± 0%  -3.96% (p=0.000 n=20)
EqualFold/UnicodePrefix-8   102.1n ± 0%   102.2n ± 0%       ~ (p=0.455 n=20)
EqualFold/UnicodeSuffix-8   90.14n ± 0%   89.80n ± 1%       ~ (p=0.113 n=20)
geomean                     71.00n        70.60n       -0.56%

Change-Id: I1f6d1df8a0398f9493692f59d7369c3f0fbba436
GitHub-Last-Rev: 9508ee26ad3cadcbb5e532a731b2553ba900f2b1
GitHub-Pull-Request: golang/go#73672
Reviewed-on: https://go-review.googlesource.com/c/go/+/671756
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/bytes/bytes.go b/src/bytes/bytes.go
index 8198415c3e193849aa9c9ca56ef990bdd9116511..a0a8fa0b2986e1e3e937de239a0da216352b9627 100644 (file)
--- a/src/bytes/bytes.go
+++ b/src/bytes/bytes.go
@@ -1228,7 +1228,7 @@ func ReplaceAll(s, old, new []byte) []byte {
 func EqualFold(s, t []byte) bool {
        // ASCII fast path
        i := 0
-       for ; i < len(s) && i < len(t); i++ {
+       for n := min(len(s), len(t)); i < n; i++ {
                sr := s[i]
                tr := t[i]
                if sr|tr >= utf8.RuneSelf {

diff --git a/src/strings/strings.go b/src/strings/strings.go
index d07a064228978f52fbea3baae0c0b9e256b49c49..d2cda74f68752e4f9fe252044601e0b07a3d65c2 100644 (file)
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -1194,7 +1194,7 @@ func ReplaceAll(s, old, new string) string {
 func EqualFold(s, t string) bool {
        // ASCII fast path
        i := 0
-       for ; i < len(s) && i < len(t); i++ {
+       for n := min(len(s), len(t)); i < n; i++ {
                sr := s[i]
                tr := t[i]
                if sr|tr >= utf8.RuneSelf {