// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "crc32c.h"

#ifdef __SSE4_2__
#include <x86intrin.h>

/* x86 version based using instrinsics */

uint32_t crc32c_hw(const char *src, size_t len) {
  const unsigned char *s = (unsigned char *)src;
  uint64_t hh = ~0;
#ifdef __x86_64__
  while (len > 7) {
    uint64_t v = *(uint64_t *)s;
    hh = _mm_crc32_u64(hh, v);
    s += 8;
    len -= 8;
  }
#endif /* __x86_64__ */
  uint32_t h = (uint32_t)hh;
  if (len > 3) {
    uint32_t v = *(uint32_t *)s;
    h = _mm_crc32_u32(h, v);
    s += 4;
    len -= 4;
  }
  if (len > 1) {
    uint16_t v = *(uint16_t *)s;
    h = _mm_crc32_u16(h, v);
    s += 2;
    len -= 2;
  }
  if (len > 0) {
    uint8_t v = *(uint8_t *)s;
    h = _mm_crc32_u8(h, v);
    s += 1;
    len -= 1;
  }
  return ~h;
}
#endif /* __SSE4_2__ */

/* CRC-32C (iSCSI) polynomial in reversed bit order. */
#define POLY 0x82f63b78

uint32_t crc32c_sw(const char *src, size_t len) {
  const unsigned char *s = (unsigned char *)src;
  uint32_t h = ~0;
  while (len--) {
    h ^= *s++;
    for (int k = 0; k < 8; k++) h = h & 1 ? (h >> 1) ^ POLY : h >> 1;
  }
  return ~h;
}

uint32_t crc32c(const char *src, size_t len) {
#ifdef __SSE4_2__
  return crc32c_hw(src, len);
#else
  return crc32c_sw(src, len);
#endif
}