string.h of eglibc

string.h

/* Return the length of S.  */
#define _HAVE_STRING_ARCH_strlen 1
#define strlen(str) \
  (__extension__ (__builtin_constant_p (str)                                  \
                  ? __builtin_strlen (str)                                    \
                  : __strlen_g (str)))
__STRING_INLINE size_t __strlen_g (__const char *__str);

__STRING_INLINE size_t
__strlen_g (__const char *__str)
{
  register char __dummy;
  register __const char *__tmp = __str;
  __asm__ __volatile__
    ("1:\n\t"
     "movb      (%0),%b1\n\t"
     "leal      1(%0),%0\n\t"
     "testb     %b1,%b1\n\t"
     "jne       1b"
     : "=r" (__tmp), "=&q" (__dummy)
     : "0" (__str),
       "m" ( *(struct { char __x[0xfffffff]; } *)__str)
     : "cc" );
  return __tmp - __str - 1;
}