#include "crc8.h"

/*
 * static uint8_t sht75_crc_table[];
 *
 * The SHT75 humidity sensor is capable of calculating an 8 bit CRC checksum to
 * ensure data integrity. The lookup table crc_table[] is used to recalculate
 * the CRC.
 */
static uint8_t sht75_crc_table[] =
    {
        0, 49, 98, 83, 196, 245, 166, 151, 185, 136, 219, 234, 125, 76, 31, 46,
        67, 114, 33, 16, 135, 182, 229, 212, 250, 203, 152, 169, 62, 15, 92, 109,
        134, 183, 228, 213, 66, 115, 32, 17, 63, 14, 93, 108, 251, 202, 153, 168,
        197, 244, 167, 150, 1, 48, 99, 82, 124, 77, 30, 47, 184, 137, 218, 235,
        61, 12, 95, 110, 249, 200, 155, 170, 132, 181, 230, 215, 64, 113, 34, 19,
        126, 79, 28, 45, 186, 139, 216, 233, 199, 246, 165, 148, 3, 50, 97, 80,
        187, 138, 217, 232, 127, 78, 29, 44, 2, 51, 96, 81, 198, 247, 164, 149,
        248, 201, 154, 171, 60, 13, 94, 111, 65, 112, 35, 18, 133, 180, 231, 214,
        122, 75, 24, 41, 190, 143, 220, 237, 195, 242, 161, 144, 7, 54, 101, 84,
        57, 8, 91, 106, 253, 204, 159, 174, 128, 177, 226, 211, 68, 117, 38, 23,
        252, 205, 158, 175, 56, 9, 90, 107, 69, 116, 39, 22, 129, 176, 227, 210,
        191, 142, 221, 236, 123, 74, 25, 40, 6, 55, 100, 85, 194, 243, 160, 145,
        71, 118, 37, 20, 131, 178, 225, 208, 254, 207, 156, 173, 58, 11, 88, 105,
        4, 53, 102, 87, 192, 241, 162, 147, 189, 140, 223, 238, 121, 72, 27, 42,
        193, 240, 163, 146, 5, 52, 103, 86, 120, 73, 26, 43, 188, 141, 222, 239,
        130, 179, 224, 209, 70, 119, 36, 21, 59, 10, 89, 104, 255, 206, 157, 172};

/*
 * uint8_t crc_8( const unsigned char *input_str, size_t num_bytes );
 *
 *函数crc_8()计算输入字符串的8位宽crc
 *给定长度。
 */
uint8_t crc_8(const uint8_t *input_str, uint16_t num_bytes)
{
    uint16_t a;
    uint8_t crc;
    const uint8_t *ptr;

    crc = CRC_START_8;
    ptr = input_str;
    if (ptr != NULL)
        for (a = 0; a < num_bytes; a++)
        {
            crc = sht75_crc_table[(*ptr++) ^ crc];
        }
    return crc;
}

/*
 * uint8_t update_crc_8( unsigned char crc, unsigned char val );
 *
 *给定一个数据字节和循环冗余校验值的前一个值
 *update_crc_8()计算并返回数据的新的实际crc值
 */

uint8_t update_crc_8(uint8_t crc, uint8_t val)
{
    return sht75_crc_table[val ^ crc];
}