[PATCH] lib/string.c: make strncmp() smaller

[PATCH] lib/string.c: make strncmp() smaller

[Alexey Dobriyan]

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;
 }

Re: [PATCH] lib/string.c: make strncmp() smaller

[Joe Perches]

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?

Re: [PATCH] lib/string.c: make strncmp() smaller

[Alexey Dobriyan]

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.