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

#define SS (sizeof(size_t))
#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)

void* memchr(const void* src, int c, size_t n) {
  const unsigned char* s = src;
  c = (unsigned char)c;
  for (; ((uintptr_t)s & ALIGN) && n && *s != c; s++, n--)
    ;
  if (n && *s != c) {
    const size_t* w;
    size_t k = ONES * c;
    for (w = (const void*)s; n >= SS && !HASZERO(*w ^ k); w++, n -= SS)
      ;
    for (s = (const void*)w; n && *s != c; s++, n--)
      ;
  }
  return n ? (void*)s : 0;
}