strlen.c raw

   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  }
  23