crc.c

/* Copyright (C) 2022-2023 Salvatore Sanfilippo -- All Rights Reserved
 * See the LICENSE file for information about the license. */

#include <stdint.h>
#include <stddef.h>

/* CRC8 with the specified initialization value 'init' and
 * polynomial 'poly'. */
uint8_t crc8(const uint8_t *data, size_t len, uint8_t init, uint8_t poly)
{
    uint8_t crc = init;
    size_t i, j;
    for (i = 0; i < len; i++) {
        crc ^= data[i];
        for (j = 0; j < 8; j++) {
            if ((crc & 0x80) != 0)
                crc = (uint8_t)((crc << 1) ^ poly);
            else
                crc <<= 1;
        }
    }
    return crc;
}

/* Sum all the specified bytes modulo 256.
 * Initialize the sum with 'init' (usually 0). */
uint8_t sum_bytes(const uint8_t *data, size_t len, uint8_t init) {
    for (size_t i = 0; i < len; i++) init += data[i];
    return init;
}

/* Perform the bitwise xor of all the specified bytes.
 * Initialize xor value with 'init' (usually 0). */
uint8_t xor_bytes(const uint8_t *data, size_t len, uint8_t init) {
    for (size_t i = 0; i < len; i++) init ^= data[i];
    return init;
}