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Fix a spelling error and add a comment about possible improvements.

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This commit is contained in:
Bruce Evans 1994-12-27 13:12:34 +00:00
parent 0c4fe20e8a
commit be0264b945
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=5243
1 changed files with 17 additions and 3 deletions
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20
lib/libc/i386/string/strncmp.S
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@ -27,11 +27,11 @@
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* $Id: strncmp.S,v 1.3 1994/03/31 14:11:02 davidg Exp $
* $Id: strncmp.S,v 1.1 1994/08/05 01:18:36 wollman Exp $
*/
#if defined(LIBC_RCS) && !defined(lint)
.asciz "$Id: strncmp.S,v 1.3 1994/03/31 14:11:02 davidg Exp $"
.asciz "$Id: strncmp.S,v 1.1 1994/08/05 01:18:36 wollman Exp $"
#endif /* LIBC_RCS and not lint */
#include "DEFS.h"
@ -54,6 +54,8 @@
* I've unrolled the loop eight times: large enough to make a
* significant difference, and small enough not to totally trash the
* cache.
*
* TODO: change all the jz's back to je for consistency.
*/
ENTRY(strncmp)
@ -75,6 +77,18 @@ L2: jz L4 /* strings are equal */
cmpb %bl,(%ecx)
jne L3
/*
* XXX it might be best to move the next 4 instructions to the end of the
* unrolled part of the loop. The unrolled part would then be
* movb n(%eax),%bl; testb %bl, %bl; je L3; cmpb n(%ecx); jne L3
* or maybe better
* movb n(%eax),%bl; cmpb n(%ecx); jne L3; testb %bl,%bl; je return_0
* for n = 0, 1, ..., 8. The end of the loop would be
* L1: addl $8,%eax; addl $8,%ecx; subl $8,%edx; cmpl $8,%edx; jae Lx
* where residual counts of 0 to 7 are handled at Lx. However, this would
* be slower for short strings. Cache effects are probably not so
* important because we are only handling a byte at a time.
*/
incl %eax
incl %ecx
decl %edx
@ -146,7 +160,7 @@ L2: jz L4 /* strings are equal */
je L1
.align 2,0x90
L3: movzbl (%eax),%eax /* unsigned comparision */
L3: movzbl (%eax),%eax /* unsigned comparison */
movzbl (%ecx),%ecx
subl %ecx,%eax
popl %ebx