#include <stdio.h>


/*
*    Generates CCITT 16-bit CRC calculation table
*
*    Copyright (c) 2022 - 2023 R.J. van der Putten, Leiden, Holland, 
*    rob at sput dot nl.
* 
*    This program is free software; you can redistribute it and/or modify
*    it under the terms of the GNU General Public License version 3 as
*    published by the Free Software Foundation.
* 
*    This program is distributed in the hope that it will be useful,
*    but WITHOUT ANY WARRANTY; without even the implied warranty of
*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*    GNU General Public License for more details.
*/


int main(void)
{
    int i, j;
    unsigned int r;

    unsigned int poly = 0x1021;

    printf("/*  CCITT 16-bit CRC calculation table  */\n\n");
    printf("unsigned int crctab[] = { \\\n\t");
    for (i = 0; i < 256; i++) {
	/*  CRC Width - 8  */
	r = i << 8;
	for (j = 0; j < 8; j++) {
	    if ((r & 0x8000) != 0) {
		/*  1xxx xxxx  xxxx xxxx  */
		r = (r << 1) ^ poly;
	    } else {
		r = r << 1;
	    }
	    r = r & 0xFFFF;
	}
	if (i != 0) {
	    if ((i % 4) == 0)
		printf("\n\t");
	    else
		printf(" ");
	}
	printf("0x%04X", r);
	if(i != 255)
	    printf(",");
    }
    printf("\n};\n\n");

    return(0);
}