2015-06-09 13:05:06

by Rasmus Villemoes

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Subject: [PATCH] drivers/video/fbdev/sis/sis_main.c: avoid repeated strlen() calls

gcc is not smart enough to realize that strlen(strbuf1) cannot be
changed by the loop body, so it is forced to recompute it, at least in
the branch containing the assignment. Avoid this by using an
equivalent stopping condition.

Signed-off-by: Rasmus Villemoes <[email protected]>
---
drivers/video/fbdev/sis/sis_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/sis/sis_main.c b/drivers/video/fbdev/sis/sis_main.c
index fcf610edf217..ea95f8bf3922 100644
--- a/drivers/video/fbdev/sis/sis_main.c
+++ b/drivers/video/fbdev/sis/sis_main.c
@@ -172,7 +172,7 @@ static void sisfb_search_mode(char *name, bool quiet)

if(strlen(name) <= 19) {
strcpy(strbuf1, name);
- for(i = 0; i < strlen(strbuf1); i++) {
+ for(i = 0; strbuf1[i]; i++) {
if(strbuf1[i] < '0' || strbuf1[i] > '9') strbuf1[i] = ' ';
}

--
2.1.3


2015-06-12 09:36:31

by Tomi Valkeinen

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Subject: Re: [PATCH] drivers/video/fbdev/sis/sis_main.c: avoid repeated strlen() calls



On 09/06/15 16:04, Rasmus Villemoes wrote:
> gcc is not smart enough to realize that strlen(strbuf1) cannot be
> changed by the loop body, so it is forced to recompute it, at least in
> the branch containing the assignment. Avoid this by using an
> equivalent stopping condition.

Does it matter? Is sisfb calling sisfb_search_mode thousands of times?

Tomi


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