src/string/stpncpy.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 char *__stpncpy(char *restrict d, const char *restrict s, size_t n)
  11 {
  12 #ifdef __GNUC__
  13         typedef size_t __attribute__((__may_alias__)) word;
  14         word *wd;
  15         const word *ws;
  16         if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) {
  17                 for (; ((uintptr_t)s & ALIGN) && n && (*d=*s); n--, s++, d++);
  18                 if (!n || !*s) goto tail;
  19                 wd=(void *)d; ws=(const void *)s;
  20                 for (; n>=sizeof(size_t) && !HASZERO(*ws);
  21                        n-=sizeof(size_t), ws++, wd++) *wd = *ws;
  22                 d=(void *)wd; s=(const void *)ws;
  23         }
  24 #endif
  25         for (; n && (*d=*s); n--, s++, d++);
  26 tail:
  27         memset(d, 0, n);
  28         return d;
  29 }
  30
  31 weak_alias(__stpncpy, stpncpy);
  32