encoding/asn1: speed up marshal by reducing allocations

Replace strings.Split by strings.IndexByte and explicit
slicing to avoid the allocation of the return slice
of strings.Split.

name     old time/op    new time/op    delta
Marshal    43.3µs ± 1%    36.7µs ± 1%  -15.23%  (p=0.000 n=9+9)

name     old alloc/op   new alloc/op   delta
Marshal    10.7kB ± 0%     9.2kB ± 0%  -13.96%  (p=0.000 n=10+10)

name     old allocs/op  new allocs/op  delta
Marshal       444 ± 0%       366 ± 0%  -17.57%  (p=0.000 n=10+10)

Change-Id: I9e727defa23f7e5fc684f246de0136fe28cf8d25
Reviewed-on: https://go-review.googlesource.com/c/go/+/231738
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/src/encoding/asn1/common.go b/src/encoding/asn1/common.go
index e2aa8bd9c5..1c712e1eff 100644
--- a/src/encoding/asn1/common.go
+++ b/src/encoding/asn1/common.go
@@ -92,7 +92,16 @@ type fieldParameters struct {
 // parseFieldParameters will parse it into a fieldParameters structure,
 // ignoring unknown parts of the string.
 func parseFieldParameters(str string) (ret fieldParameters) {
-	for _, part := range strings.Split(str, ",") {
+	var part string
+	for len(str) > 0 {
+		// This loop uses IndexByte and explicit slicing
+		// instead of strings.Split(str, ",") to reduce allocations.
+		i := strings.IndexByte(str, ',')
+		if i < 0 {
+			part, str = str, ""
+		} else {
+			part, str = str[:i], str[i+1:]
+		}
 		switch {
 		case part == "optional":
 			ret.optional = true