fusl/src/string/stpcpy.c

#include <string.h>
#include <stdint.h>
#include <limits.h>
#include "libc.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)

char* __stpcpy(char* restrict d, const char* restrict s) {
  size_t* wd;
  const size_t* ws;

  if ((uintptr_t)s % ALIGN == (uintptr_t)d % ALIGN) {
    for (; (uintptr_t)s % ALIGN; s++, d++)
      if (!(*d = *s))
        return d;
    wd = (void*)d;
    ws = (const void*)s;
    for (; !HASZERO(*ws); *wd++ = *ws++)
      ;
    d = (void*)wd;
    s = (const void*)ws;
  }
  for (; (*d = *s); s++, d++)
    ;

  return d;
}

weak_alias(__stpcpy, stpcpy);