buzz simple crc_check cross-check

gistfile1.txt

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>     /* srand, rand */
#include <time.h>       /* time */


// AP_Math/crc.cpp

/*
  xmodem CRC thanks to avr-liberty
  https://github.com/dreamiurg/avr-liberty
 */
uint16_t crc_xmodem_update(uint16_t crc, uint8_t data)
{
    crc = crc ^ ((uint16_t)data << 8);
    for (uint16_t i=0; i<8; i++)
    {
        if(crc & 0x8000) {
            crc = (crc << 1) ^ 0x1021;
        } else {
            crc <<= 1;
        }
    }

    return crc;
}

uint16_t crc_xmodem(const uint8_t *data, uint16_t len)
{
    uint16_t crc = 0;
    for (uint16_t i=0; i<len; i++) {
        crc = crc_xmodem_update(crc, data[i]);
    }
    return crc;
}


// libraries/AP_HAL/utility/srxl.cpp

static uint16_t srxl_crc16 (uint16_t crc, uint8_t new_byte)
{
    uint8_t loop;
    crc = crc ^ (uint16_t)new_byte << 8;
    for(loop = 0; loop < 8; loop++) {
        crc = (crc & 0x8000) ? (crc << 1) ^ 0x1021 : (crc << 1);
    }
    return crc;
}




//libraries/AP_HAL/utility/sumd.cpp


static uint16_t sumd_crc16(uint16_t crc, uint8_t value)
{
    int i;
    crc ^= (uint16_t)value << 8;

    for (i = 0; i < 8; i++) {
        crc = (crc & 0x8000) ? (crc << 1) ^ 0x1021 : (crc << 1);
    }

    return crc;
}

int main() { 

    srand (time(NULL));

    uint16_t b = 0;

    uint16_t f1 = 0;
    uint16_t f2 = 0;    
    uint16_t f3 = 0;
    for (b = 1 ; b<1000 ; b++ ) { 
           printf("%d\n",b);
            uint16_t data = rand();
            f1 = srxl_crc16(f1,data);
            f2 = crc_xmodem_update(f2,data);        
            f3 = sumd_crc16(f3,data);
    }
    printf("%d\n",f1);
    printf("%d\n",f2);
    printf("%d\n",f3);
    return 0;
}