* [PATCH] lib/string.c: make strncmp() smaller
@ 2019-02-08 7:34 Alexey Dobriyan
2019-02-08 9:31 ` Joe Perches
0 siblings, 1 reply; 3+ messages in thread
From: Alexey Dobriyan @ 2019-02-08 7:34 UTC (permalink / raw)
To: akpm; +Cc: linux-kernel
Space savings on x86_64:
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-29 (-29)
Function old new delta
strncmp 67 38 -29
Space savings on arm:
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-60 (-60)
Function old new delta
strncmp 116 56 -60
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---
lib/string.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
--- a/lib/string.c
+++ b/lib/string.c
@@ -344,16 +344,14 @@ EXPORT_SYMBOL(strcmp);
*/
int strncmp(const char *cs, const char *ct, size_t count)
{
- unsigned char c1, c2;
+ while (count--) {
+ unsigned int c1 = *(unsigned char *)cs++;
+ unsigned int c2 = *(unsigned char *)ct++;
- while (count) {
- c1 = *cs++;
- c2 = *ct++;
if (c1 != c2)
- return c1 < c2 ? -1 : 1;
+ return c1 - c2;
if (!c1)
break;
- count--;
}
return 0;
}
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] lib/string.c: make strncmp() smaller
2019-02-08 7:34 [PATCH] lib/string.c: make strncmp() smaller Alexey Dobriyan
@ 2019-02-08 9:31 ` Joe Perches
2019-02-09 13:02 ` Alexey Dobriyan
0 siblings, 1 reply; 3+ messages in thread
From: Joe Perches @ 2019-02-08 9:31 UTC (permalink / raw)
To: Alexey Dobriyan, akpm; +Cc: linux-kernel
On Fri, 2019-02-08 at 10:34 +0300, Alexey Dobriyan wrote:
> Space savings on x86_64:
>
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-29 (-29)
> Function old new delta
> strncmp 67 38 -29
>
> Space savings on arm:
>
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-60 (-60)
> Function old new delta
> strncmp 116 56 -60
[]
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -344,16 +344,14 @@ EXPORT_SYMBOL(strcmp);
> */
> int strncmp(const char *cs, const char *ct, size_t count)
> {
> - unsigned char c1, c2;
> + while (count--) {
> + unsigned int c1 = *(unsigned char *)cs++;
> + unsigned int c2 = *(unsigned char *)ct++;
>
> - while (count) {
> - c1 = *cs++;
> - c2 = *ct++;
> if (c1 != c2)
> - return c1 < c2 ? -1 : 1;
> + return c1 - c2;
This does change the return value for most comparisons.
Wasn't there a specific reason for -1 and 1?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] lib/string.c: make strncmp() smaller
2019-02-08 9:31 ` Joe Perches
@ 2019-02-09 13:02 ` Alexey Dobriyan
0 siblings, 0 replies; 3+ messages in thread
From: Alexey Dobriyan @ 2019-02-09 13:02 UTC (permalink / raw)
To: Joe Perches; +Cc: akpm, linux-kernel
On Fri, Feb 08, 2019 at 01:31:49AM -0800, Joe Perches wrote:
> On Fri, 2019-02-08 at 10:34 +0300, Alexey Dobriyan wrote:
> > - return c1 < c2 ? -1 : 1;
> > + return c1 - c2;
>
> This does change the return value for most comparisons.
It does.
> Wasn't there a specific reason for -1 and 1?
Maybe. Spec says anything positive or negative works.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-02-08 7:34 [PATCH] lib/string.c: make strncmp() smaller Alexey Dobriyan
2019-02-08 9:31 ` Joe Perches
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