fusl/src/string/strlcpy.c

#define _BSD_SOURCE
#include <string.h>
#include <stdint.h>
#include <limits.h>
#include "libc.h"

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

size_t strlcpy(char* d, const char* s, size_t n) {
  char* d0 = d;
  size_t* wd;
  const size_t* ws;

  if (!n--)
    goto finish;
  if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) {
    for (; ((uintptr_t)s & ALIGN) && n && (*d = *s); n--, s++, d++)
      ;
    if (n && *s) {
      wd = (void*)d;
      ws = (const void*)s;
      for (; n >= sizeof(size_t) && !HASZERO(*ws);
           n -= sizeof(size_t), ws++, wd++)
        *wd = *ws;
      d = (void*)wd;
      s = (const void*)ws;
    }
  }
  for (; n && (*d = *s); n--, s++, d++)
    ;
  *d = 0;
finish:
  return d - d0 + strlen(s);
}