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];
  }
}

static 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(void *crc_calculator, uint8_t *p, int length) {
  CRC_CALCULATOR *p_crc_calculator = (CRC_CALCULATOR *)crc_calculator;
  crc_calculator_reset(p_crc_calculator);
  crc_calculator_process_data(p_crc_calculator, p, length);
  return crc_calculator_get_crc(p_crc_calculator);
}

/* 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(CRC32C *p, uint8_t *buf, size_t len) {
  const uint8_t *next = (const uint8_t *)(buf);
  uint64_t crc;

  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;
}