#include <limits.h>
#include <stdint.h>
#include <string.h>
#include <zircon/compiler.h>

#define ALIGN (sizeof(size_t))
#define ONES ((size_t)-1 / UCHAR_MAX)
#define HIGHS (ONES * (UCHAR_MAX / 2 + 1))
#define HASZERO(x) (((x)-ONES) & ~(x)&HIGHS)

size_t strlen(const char* s) {
  const char* a = s;
  for (; (uintptr_t)s % ALIGN; s++)
    if (!*s)
      return s - a;
  const size_t* w = (const void*)s;
#if !__has_feature(address_sanitizer)
  // This reads past the end of the string, which is usually OK since it
  // won't cross a page boundary.  But under ASan, even one byte past the
  // actual end is diagnosed.
  while (!HASZERO(*w))
    ++w;
#endif
  for (s = (const void*)w; *s; s++)
    ;
  return s - a;
}