trezor-firmware/core/embed/io/nrf/crc8.c

/*
 * Copyright (c) 2020 Intel Corporation
 * Copyright (c) 2017 Nordic Semiconductor ASA
 * Copyright (c) 2015 Runtime Inc
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include "crc8.h"

static const uint8_t crc8_ccitt_small_table[16] = {
    0x00, 0x07, 0x0e, 0x09, 0x1c, 0x1b, 0x12, 0x15,
    0x38, 0x3f, 0x36, 0x31, 0x24, 0x23, 0x2a, 0x2d};

uint8_t crc8_ccitt(uint8_t val, const void *buf, size_t cnt) {
  size_t i;
  const uint8_t *p = buf;

  for (i = 0; i < cnt; i++) {
    val ^= p[i];
    val = (val << 4) ^ crc8_ccitt_small_table[val >> 4];
    val = (val << 4) ^ crc8_ccitt_small_table[val >> 4];
  }
  return val;
}

uint8_t crc8(const uint8_t *src, size_t len, uint8_t polynomial,
             uint8_t initial_value, bool reversed) {
  uint8_t crc = initial_value;
  size_t i, j;

  for (i = 0; i < len; i++) {
    crc ^= src[i];

    for (j = 0; j < 8; j++) {
      if (reversed) {
        if (crc & 0x01) {
          crc = (crc >> 1) ^ polynomial;
        } else {
          crc >>= 1;
        }
      } else {
        if (crc & 0x80) {
          crc = (crc << 1) ^ polynomial;
        } else {
          crc <<= 1;
        }
      }
    }
  }

  return crc;
}