#include "crc16.h"

static uint8_t crc_tab16_init = 0;
static uint16_t crc_tab16[256] = {
        0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48, 0x9dc1, 0xaf5a, 0xbed3,
        0xca6c, 0xdbe5, 0xe97e, 0xf8f7, 0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
        0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876, 0x2102, 0x308b, 0x0210, 0x1399,
        0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
        0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c, 0xbdcb, 0xac42, 0x9ed9, 0x8f50,
        0xfbef, 0xea66, 0xd8fd, 0xc974, 0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
        0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, 0x5285, 0x430c, 0x7197, 0x601e,
        0x14a1, 0x0528, 0x37b3, 0x263a, 0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
        0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5,
        0xa96a, 0xb8e3, 0x8a78, 0x9bf1, 0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
        0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70, 0x8408, 0x9581, 0xa71a, 0xb693,
        0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
        0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 0x18c1, 0x0948, 0x3bd3, 0x2a5a,
        0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
        0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 0xb58b, 0xa402, 0x9699, 0x8710,
        0xf3af, 0xe226, 0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
        0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df,
        0x0c60, 0x1de9, 0x2f72, 0x3efb, 0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
        0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, 0xe70e, 0xf687, 0xc41c, 0xd595,
        0xa12a, 0xb0a3, 0x8238, 0x93b1, 0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
        0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c,
        0x3de3, 0x2c6a, 0x1ef1, 0x0f78};

/*
 * uint16_t crc_16( const unsigned char *input_str, size_t num_bytes );
 *
 *函数crc_16()一次计算一个字节的16位CRC16
 *其开头已传递给函数的字符串。的数量
 *要检查的字节也是一个参数。字符串中的字节数为
 *受恒定大小最大值的限制。
 */
uint16_t crc_16(const uint8_t *input_str, uint16_t num_bytes) {
//    uint16_t crc;
//    const uint8_t *ptr;
//    uint16_t a;
////    if (!crc_tab16_init)
////        init_crc16_tab();
//    crc = CRC_START_16;
//    ptr = input_str;
//    if (ptr != NULL)
//        for (a = 0; a < num_bytes; a++) {
//            crc = (crc >> 8) ^ crc_tab16[(crc ^ (uint16_t) *ptr++) & 0x00FF];
//        }
//    return crc;
    uint8_t ch_data;
    uint16_t wCRC = 0xFFFF;

    if (input_str == NULL) return 0xFFFF;
    while (num_bytes--) {
        ch_data = *input_str++;
        (wCRC) =
                ((uint16_t)(wCRC) >> 8) ^ crc_tab16[((uint16_t)(wCRC) ^ (uint16_t)(ch_data)) & 0x00ff];
    }
    return wCRC;
}

/*
 * uint16_t crc_modbus( const unsigned char *input_str, size_t num_bytes );
 *
 *函数crc_modbus()一次计算16位modbus循环冗余校验
 *一个字节字符串，其开头已被传递给函数。这
 *要检查的字节数也是一个参数。
 */

uint16_t crc_modbus(const uint8_t *input_str, uint16_t num_bytes) {
    uint16_t crc;
    const uint8_t *ptr;
    uint16_t a;

    if (!crc_tab16_init)
        init_crc16_tab();

    crc = CRC_START_MODBUS;
    ptr = input_str;
    if (ptr != NULL)
        for (a = 0; a < num_bytes; a++) {

            crc = (crc >> 8) ^ crc_tab16[(crc ^ (uint16_t) *ptr++) & 0x00FF];
        }
    return crc;
}

/*
 * uint16_t update_crc_16( uint16_t crc, unsigned char c );
 *
 *函数update_crc_16()根据
 *前一个循环冗余校验值和下一个要检查的数据字节。
 */
uint16_t update_crc_16(uint16_t crc, uint8_t c) {
    if (!crc_tab16_init)
        init_crc16_tab();
    return (crc >> 8) ^ crc_tab16[(crc ^ (uint16_t) c) & 0x00FF];
}

/*
 * static void init_crc16_tab( void );
 *
 *为了获得最佳性能，使用CRC16例程查找带有值的表
 *可以直接在异或算法中使用的算法。
 *查找表首次由init_crc16_tab()例程计算
 *调用循环冗余校验函数。
 */
void init_crc16_tab(void) {
    uint16_t i;
    uint16_t j;
    uint16_t crc;
    uint16_t c;
    for (i = 0; i < 256; i++) {
        crc = 0;
        c = i;
        for (j = 0; j < 8; j++) {
            if ((crc ^ c) & 0x0001)
                crc = (crc >> 1) ^ CRC_POLY_16;
            else
                crc = crc >> 1;
            c = c >> 1;
        }
        crc_tab16[i] = crc;
    }
    crc_tab16_init = 1;
}

uint32_t VerifyCRC16CheckSum(uint8_t *pchMessage, uint32_t dwLength) {
    uint16_t wExpected = 0;
    if ((pchMessage == NULL) || (dwLength <= 2)) {
        return 0;
    }
    wExpected = crc_16(pchMessage, dwLength - 2);
    return ((wExpected & 0xff) == pchMessage[dwLength - 2] && ((wExpected >> 8) & 0xff) == pchMessage[dwLength - 1]);
}