Implementation of xxHash for small input

xxhash.c

#include <stdlib.h>
#include <intrin.h>

#define PRIME32_1 0x9E3779B1
#define PRIME32_2 0x85EBCA77
#define PRIME32_3 0xC2B2AE3D
#define PRIME32_4 0x27D4EB2F
#define PRIME32_5 0x165667B1

uint32_t xxHash(const char *input, size_t size, uint32_t seed) {
  size_t index;
  uint32_t hash = seed + size + PRIME32_5;
  for (index = 0; size - index >= 4; index += 4) {
    uint32_t value;
    memcpy(&value, input + index, sizeof(value));
    hash += value * PRIME32_3;
    hash = _rotl(hash, 17) * PRIME32_4;
  }
  for (; index < size; index++) {
    uint8_t value = input[index];
    hash += value * PRIME32_5;
    hash = _rotl(hash, 11) * PRIME32_1;
  }
  hash ^= hash >> 15;
  hash *= PRIME32_2;
  hash ^= hash >> 13;
  hash *= PRIME32_3;
  return hash ^ hash >> 16;
}