stm32_crc.c

#include <unistd.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>

#define POLY 0x04C11DB7

uint32_t crc_table[256];

uint32_t update_crc_slow_1byte(uint32_t crc, uint32_t data) {
        crc ^= data;

        for (int i = 0; i < 8; i++) {
                if (crc & 0x80000000) {
                        crc = (crc << 1) ^ POLY;
                } else {
                        crc = (crc << 1);
                }
        }

        return crc;
}

void mk_table() {
        for (uint32_t i = 0; i < 256; i++) {
                crc_table[i] = update_crc_slow_1byte(0, i << 24);
        }
}

uint32_t update_crc_fast_byte(uint32_t crc, uint8_t data) {
        uint32_t ent = (crc >> 24) ^ data;
        return (crc << 8) ^ crc_table[ent];
}

uint32_t update_crc(uint32_t crc, uint32_t data) {
        crc = update_crc_fast_byte(crc, (data >> 24) & 0xFF);
        crc = update_crc_fast_byte(crc, (data >> 16) & 0xFF);
        crc = update_crc_fast_byte(crc, (data >>  8) & 0xFF);
        crc = update_crc_fast_byte(crc, (data      ) & 0xFF);

        return crc;
}

int main() {
        uint8_t buf[1024];
        size_t len;

        mk_table();

        if (getenv("PRINT_TABLE")) {
                printf("uint32_t crc_table[] = {");

                for (uint32_t i = 0; i < 256; i++) {
                        printf("%s0x%08x, ", (i % 8 == 0) ? "\n\t" : "", crc_table[i]);
                }
                printf("\n};\n");
                exit(0);
        }

        len = read(0, buf, sizeof(buf));

        uint32_t crc = 0xffffffff;
        uint32_t *bufp = (uint32_t *)buf;
        while (len >= 4) {
                crc = update_crc(crc, *bufp);

                bufp++;
                len -= 4;
        }

        /* The last word is kind of funky -- it's little-endian justified,
         * big-endian.  */
        if (len > 0) {
                uint32_t word = 0x0;
                uint8_t *bufp8 = (uint8_t *)bufp;
                for (int i = 0; i < len; i++) {
                        word |= bufp8[i] << ((len - i - 1) * 8);
                }

                crc = update_crc(crc, word);
                len -= len;
        }

        printf("crc: %08x\n", crc);

        return 0;
}