fusl/src/string/memmove.c

#include <string.h>
#include <stdint.h>

#define WT size_t
#define WS (sizeof(WT))

void* memmove(void* dest, const void* src, size_t n) {
  char* d = dest;
  const char* s = src;

  if (d == s)
    return d;
  if (s + n <= d || d + n <= s)
    return memcpy(d, s, n);

  if (d < s) {
    if ((uintptr_t)s % WS == (uintptr_t)d % WS) {
      while ((uintptr_t)d % WS) {
        if (!n--)
          return dest;
        *d++ = *s++;
      }
      for (; n >= WS; n -= WS, d += WS, s += WS)
        *(WT*)d = *(WT*)s;
    }
    for (; n; n--)
      *d++ = *s++;
  } else {
    if ((uintptr_t)s % WS == (uintptr_t)d % WS) {
      while ((uintptr_t)(d + n) % WS) {
        if (!n--)
          return dest;
        d[n] = s[n];
      }
      while (n >= WS)
        n -= WS, *(WT*)(d + n) = *(WT*)(s + n);
    }
    while (n)
      n--, d[n] = s[n];
  }

  return dest;
}