On Tue, 2003-08-12 at 22:47, Erik Andersen wrote:
On Tue Aug 12, 2003 at 10:18:21PM -0400, Albert Cahalan wrote:
You're all wrong. This is some kind of programmingchar *strncpy(char * s1, const char * s2, size_t n)
test for sure!
Let us imagine that glibc has a correct version.
By exhaustive testing, I found a version that works.
Here it is, along with the test code:
//////////////////////////////////////////////////////
#define _GNU_SOURCE
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
// first correct implementation!
char * strncpy_good(char *dest, const char *src, size_t count){
char *tmp = dest;
memset(dest,'\0',count);
while (count-- && (*tmp++ = *src++))
;
return dest;
}
{
register char *s = s1;
while (n) {
if ((*s = *s2) != 0) s2++;
++s;
--n;
}
return s1;
}
That's excellent. On ppc I count 12 instructions,
4 of which would go away for typical usage if inlined.
Annoyingly, gcc doesn't get the same assembly from my
attempt at that general idea:
char * strncpy_5(char *dest, const char *src, size_t count){
char *tmp = dest;
while (count--){
if(( *tmp++ = *src )) src++;
}
return dest;
}
I suppose that gcc could use a bug report.