src/string/memccpy.c

   1 #include <string.h>
   2 #include <stdint.h>
   3 #include <limits.h>
   4
   5 #define ALIGN (sizeof(size_t)-1)
   6 #define ONES ((size_t)-1/UCHAR_MAX)
   7 #define HIGHS (ONES * (UCHAR_MAX/2+1))
   8 #define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
   9
  10 void *memccpy(void *restrict dest, const void *restrict src, int c, size_t n)
  11 {
  12         unsigned char *d = dest;
  13         const unsigned char *s = src;
  14
  15         c = (unsigned char)c;
  16 #ifdef __GNUC__
  17         typedef size_t __attribute__((__may_alias__)) word;
  18         word *wd;
  19         const word *ws;
  20         if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) {
  21                 for (; ((uintptr_t)s & ALIGN) && n && (*d=*s)!=c; n--, s++, d++);
  22                 if ((uintptr_t)s & ALIGN) goto tail;
  23                 size_t k = ONES * c;
  24                 wd=(void *)d; ws=(const void *)s;
  25                 for (; n>=sizeof(size_t) && !HASZERO(*ws^k);
  26                        n-=sizeof(size_t), ws++, wd++) *wd = *ws;
  27                 d=(void *)wd; s=(const void *)ws;
  28         }
  29 #endif
  30         for (; n && (*d=*s)!=c; n--, s++, d++);
  31 tail:
  32         if (n) return d+1;
  33         return 0;
  34 }