On Sun, 2015-06-28 at 19:44 +0300, Alexey Dobriyan wrote:
> Commit 8da53d4595a53fb9a3380dd4d1c9bc24c7c9aab8
> ("lib/string.c: improve strrchr()") changed strrchr() implementation
> from "rewind to the end and search backwards" to "search forward"
> optimizing for characher not found case. However, common case is exactly
> the opposite: string is absolute pathname, c is '/' always to be found.
>
> Previous code did 1 branch per character + 1 branch for every character
> in the last path component. Current code does 2 branches per characher
> regardless.
Are you comparing total cycles of all of the branches
in the called functions too?
As written the current version removes the strlen call.
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -313,12 +313,13 @@ EXPORT_SYMBOL(strchrnul);
> */
> char *strrchr(const char *s, int c)
> {
> - const char *last = NULL;
> + const char *p = s + strlen(s);
> +
> do {
> - if (*s == (char)c)
> - last = s;
> - } while (*s++);
> - return (char *)last;
> + if (*p == (char)c)
> + return (char *)p;
> + } while (--p >= s);
> + return NULL;
> }
> EXPORT_SYMBOL(strrchr);
> #endif
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