Messages in this thread | | | Subject | Re: generic strncpy - off-by-one error | From | Albert Cahalan <> | Date | 12 Aug 2003 23:38:31 -0400 |
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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 programming > > 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; > > } > > char *strncpy(char * s1, const char * s2, size_t n) > { > 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.
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