av1/encoder/hash.c

/*
 * 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"

static void crc_calculator_process_data(CRC_CALCULATOR *p_crc_calculator,
                                        uint8_t *pData, uint32_t dataLength) {
  for (uint32_t i = 0; i < dataLength; i++) {
    const uint8_t index =
        (p_crc_calculator->remainder >> (p_crc_calculator->bits - 8)) ^
        pData[i];
    p_crc_calculator->remainder <<= 8;
    p_crc_calculator->remainder ^= p_crc_calculator->table[index];
  }
}

void crc_calculator_reset(CRC_CALCULATOR *p_crc_calculator) {
  p_crc_calculator->remainder = 0;
}

static uint32_t crc_calculator_get_crc(CRC_CALCULATOR *p_crc_calculator) {
  return p_crc_calculator->remainder & p_crc_calculator->final_result_mask;
}

static void crc_calculator_init_table(CRC_CALCULATOR *p_crc_calculator) {
  const uint32_t high_bit = 1 << (p_crc_calculator->bits - 1);
  const uint32_t byte_high_bit = 1 << (8 - 1);

  for (uint32_t value = 0; value < 256; value++) {
    uint32_t remainder = 0;
    for (uint8_t mask = byte_high_bit; mask != 0; mask >>= 1) {
      if (value & mask) {
        remainder ^= high_bit;
      }

      if (remainder & high_bit) {
        remainder <<= 1;
        remainder ^= p_crc_calculator->trunc_poly;
      } else {
        remainder <<= 1;
      }
    }
    p_crc_calculator->table[value] = remainder;
  }
}

void av1_crc_calculator_init(CRC_CALCULATOR *p_crc_calculator, uint32_t bits,
                             uint32_t truncPoly) {
  p_crc_calculator->remainder = 0;
  p_crc_calculator->bits = bits;
  p_crc_calculator->trunc_poly = truncPoly;
  p_crc_calculator->final_result_mask = (1 << bits) - 1;
  crc_calculator_init_table(p_crc_calculator);
}

uint32_t av1_get_crc_value(CRC_CALCULATOR *p_crc_calculator, uint8_t *p,
                           int length) {
  crc_calculator_reset(p_crc_calculator);
  crc_calculator_process_data(p_crc_calculator, p, length);
  return crc_calculator_get_crc(p_crc_calculator);
}