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

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

#ifdef __GNUC__

#if __BYTE_ORDER == __LITTLE_ENDIAN
#define LS >>
#define RS <<
#else
#define LS <<
#define RS >>
#endif

  typedef uint32_t __attribute__((__may_alias__)) u32;
  uint32_t w, x;

  for (; (uintptr_t)s % 4 && n; n--)
    *d++ = *s++;

  if ((uintptr_t)d % 4 == 0) {
    for (; n >= 16; s += 16, d += 16, n -= 16) {
      *(u32*)(d + 0) = *(u32*)(s + 0);
      *(u32*)(d + 4) = *(u32*)(s + 4);
      *(u32*)(d + 8) = *(u32*)(s + 8);
      *(u32*)(d + 12) = *(u32*)(s + 12);
    }
    if (n & 8) {
      *(u32*)(d + 0) = *(u32*)(s + 0);
      *(u32*)(d + 4) = *(u32*)(s + 4);
      d += 8;
      s += 8;
    }
    if (n & 4) {
      *(u32*)(d + 0) = *(u32*)(s + 0);
      d += 4;
      s += 4;
    }
    if (n & 2) {
      *d++ = *s++;
      *d++ = *s++;
    }
    if (n & 1) {
      *d = *s;
    }
    return dest;
  }

  if (n >= 32)
    switch ((uintptr_t)d % 4) {
      case 1:
        w = *(u32*)s;
        *d++ = *s++;
        *d++ = *s++;
        *d++ = *s++;
        n -= 3;
        for (; n >= 17; s += 16, d += 16, n -= 16) {
          x = *(u32*)(s + 1);
          *(u32*)(d + 0) = (w LS 24) | (x RS 8);
          w = *(u32*)(s + 5);
          *(u32*)(d + 4) = (x LS 24) | (w RS 8);
          x = *(u32*)(s + 9);
          *(u32*)(d + 8) = (w LS 24) | (x RS 8);
          w = *(u32*)(s + 13);
          *(u32*)(d + 12) = (x LS 24) | (w RS 8);
        }
        break;
      case 2:
        w = *(u32*)s;
        *d++ = *s++;
        *d++ = *s++;
        n -= 2;
        for (; n >= 18; s += 16, d += 16, n -= 16) {
          x = *(u32*)(s + 2);
          *(u32*)(d + 0) = (w LS 16) | (x RS 16);
          w = *(u32*)(s + 6);
          *(u32*)(d + 4) = (x LS 16) | (w RS 16);
          x = *(u32*)(s + 10);
          *(u32*)(d + 8) = (w LS 16) | (x RS 16);
          w = *(u32*)(s + 14);
          *(u32*)(d + 12) = (x LS 16) | (w RS 16);
        }
        break;
      case 3:
        w = *(u32*)s;
        *d++ = *s++;
        n -= 1;
        for (; n >= 19; s += 16, d += 16, n -= 16) {
          x = *(u32*)(s + 3);
          *(u32*)(d + 0) = (w LS 8) | (x RS 24);
          w = *(u32*)(s + 7);
          *(u32*)(d + 4) = (x LS 8) | (w RS 24);
          x = *(u32*)(s + 11);
          *(u32*)(d + 8) = (w LS 8) | (x RS 24);
          w = *(u32*)(s + 15);
          *(u32*)(d + 12) = (x LS 8) | (w RS 24);
        }
        break;
    }
  if (n & 16) {
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
  }
  if (n & 8) {
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
  }
  if (n & 4) {
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
    *d++ = *s++;
  }
  if (n & 2) {
    *d++ = *s++;
    *d++ = *s++;
  }
  if (n & 1) {
    *d = *s;
  }
  return dest;
#endif

  for (; n; n--)
    *d++ = *s++;
  return dest;
}