/*

 * Copyright (c) 2016, Alliance for Open Media. All rights reserved.

 *

 * This source code is subject to the terms of the BSD 2 Clause License and

 * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License

 * was not distributed with this source code in the LICENSE file, you can

 * obtain it at www.aomedia.org/license/software. If the Alliance for Open

 * Media Patent License 1.0 was not distributed with this source code in the

 * PATENTS file, you can obtain it at www.aomedia.org/license/patent.

 */

#include "av1/encoder/hash.h"

#include <stddef.h>

#include <string.h>

#include "config/av1_rtcd.h"

/* CRC-32C (iSCSI) polynomial in reversed bit order. */

#define POLY 0x82f63b78

/* Construct table for software CRC-32C calculation. */

void av1_crc32c_calculator_init(CRC32C *p_crc32c) {

  uint32_t crc;

  for (int n = 0; n < 256; n++) {

    crc = n;

    crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;

    crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;

    crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;

    crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;

    crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;

    crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;

    crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;

    crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;

    p_crc32c->table[0][n] = crc;

  }

  for (int n = 0; n < 256; n++) {

    crc = p_crc32c->table[0][n];

    for (int k = 1; k < 8; k++) {

      crc = p_crc32c->table[0][crc & 0xff] ^ (crc >> 8);

      p_crc32c->table[k][n] = crc;

    }

  }

}

/* Table-driven software version as a fall-back.  This is about 15 times slower

 than using the hardware instructions.  This assumes little-endian integers,

 as is the case on Intel processors that the assembler code here is for. */

uint32_t av1_get_crc32c_value_c(void *c, const uint8_t *buf, size_t len) {

  const uint8_t *next = buf;

  uint64_t crc;

  CRC32C *p = (CRC32C *)c;

  crc = 0 ^ 0xffffffff;

  while (len && ((uintptr_t)next & 7) != 0) {

    crc = p->table[0][(crc ^ *next++) & 0xff] ^ (crc >> 8);

    len--;

  }

  while (len >= 8) {

    crc ^= *(uint64_t *)next;

    crc = p->table[7][crc & 0xff] ^ p->table[6][(crc >> 8) & 0xff] ^

          p->table[5][(crc >> 16) & 0xff] ^ p->table[4][(crc >> 24) & 0xff] ^

          p->table[3][(crc >> 32) & 0xff] ^ p->table[2][(crc >> 40) & 0xff] ^

          p->table[1][(crc >> 48) & 0xff] ^ p->table[0][crc >> 56];

    next += 8;

    len -= 8;

  }

  while (len) {

    crc = p->table[0][(crc ^ *next++) & 0xff] ^ (crc >> 8);

    len--;

  }

  return (uint32_t)crc ^ 0xffffffff;

}

// For each of the width positions in a row, hashes the 4 sub-block hashes at

// that position and sub_size to the right of it, in top and then in bottom.

// The two rows are separate pointers so they can come from a ring buffer.

void av1_combine_block_hashes_c(void *crc_calculator, const uint32_t *top,

                                const uint32_t *bottom, uint32_t *dst,

                                int width, int sub_size) {

  for (int x = 0; x < width; x++) {

    const uint32_t v[4] = { top[x], top[x + sub_size], bottom[x],

                            bottom[x + sub_size] };

    // Hash a byte copy so the static analyzer can follow the byte reads.

    // TODO: bug aomedia:433531610 - serialize input values in a way that's

    // independent of the computer architecture's endianness

    uint8_t p[sizeof(v)];

    memcpy(p, v, sizeof(v));

    dst[x] = av1_get_crc32c_value_c(crc_calculator, p, sizeof(p));

  }

}