src/string/strlen.c

   1 #include <string.h>
   2 #include <stdint.h>
   3 #include <limits.h>
   4
   5 #define ALIGN (sizeof(size_t))
   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 size_t strlen(const char *s)
  11 {
  12         const char *a = s;
  13 #ifdef __GNUC__
  14         typedef size_t __attribute__((__may_alias__)) word;
  15         const word *w;
  16         for (; (uintptr_t)s % ALIGN; s++) if (!*s) return s-a;
  17         for (w = (const void *)s; !HASZERO(*w); w++);
  18         s = (const void *)w;
  19 #endif
  20         for (; *s; s++);
  21         return s-a;
  22 }