From: Rob Pike <r@golang.org>
Date: Mon, 7 Dec 2009 19:28:02 +0000 (-0800)
Subject: pick off special one-byte case in copy. worth 2x in benchmarks (38ns->16ns).
X-Git-Tag: weekly.2009-12-07~6
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=20c1ec263a8910ae1b794cb017f59e73997a9296;p=gostls13.git

pick off special one-byte case in copy. worth 2x in benchmarks (38ns->16ns).
the one-item case could be generalized easily with no cost. worth considering.

R=rsc
CC=golang-dev, cw
https://golang.org/cl/167044
---

diff --git a/src/pkg/runtime/slice.c b/src/pkg/runtime/slice.c
index ba4be331b5..1d7a56e7ba 100644
--- a/src/pkg/runtime/slice.c
+++ b/src/pkg/runtime/slice.c
@@ -208,7 +208,11 @@ runtime·slicecopy(Slice to, Slice fm, uintptr width, int32 ret)
 	if(to.len < ret)
 		ret = to.len;
 
-	memmove(to.array, fm.array, ret*width);
+	if(ret == 1 && width == 1) {	// common case worth about 2x to do here
+		*to.array = *fm.array;	// known to be a byte pointer
+	} else {
+		memmove(to.array, fm.array, ret*width);
+	}
 
 out:
 	FLUSH(&ret);