/* WilChkSm.c - a checksum calculator for Williams ROM images */
/* Version 1.1 7-FEB-95 */
/* Copyright © 1995 Sean Riddle */

/* Freely distributable on any medium given all copyrights are retained */
/* by the author and no charge greater than $7.00 is made for obtaining */
/* this software */

/* Please send all bug reports and update ideas to: */
/* sriddle@ionet.net */

/* latest version at: */
/* <a href="http://www.ionet.net/~sriddle">Please don't hurl on my URL!</a> */

/* usage: WilChkSm <file>  */

/* This program takes a Williams ROM image and calculates the checksum */
/* for each ROM.  It then compares each checksum to the checksum table */
/* and reports any errors.  The ROM image can be a single file that's */
/* 65536 bytes long, or twelve 4096-byte files, representing each ROM. */
/* The 12 files must be named <file>.nn, where nn goes from 01 through 12. */

/* NOTE: the range 9000-CFFF should be all FFs.  This is RAM and I/O. */

/* WilChkSm has been tested on the games Stargate, Robotron, Joust, */
/* Bubbles and Sinistar */

/* history: */
/* 2/7/95 - slight changes to work with Sinistar.xx files - there are */
/*          fewer than 12 of these. */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void main(int argc, char *argv[]) {
   FILE *fp;
   char *buffer;
   char sum;
   int r,x,y;
   int chksumoff=0;
   char file[256];
   int loop;
   int noerror=1;

   if(argc==2) {
      if(!(buffer=malloc(65536)))
         printf("no memory for ROM buffer\n");
      else {
         for(x=0;x<65535;x++)
            buffer[x]=-1;
         loop=0;
         if(fp=fopen(argv[1],"rb")) {
            fread(buffer,65536,1,fp);
            fclose(fp);
            loop=-1;
         } else {
            for(x=1;(x<13);x++) {
               if(x<10)
                  y=x;
               else
                  y=x+4;
               sprintf(file,"%s.%02.2d",argv[1],x);
               if(fp=fopen(file,"rb")) {
                  fread(&buffer[(y-1)*4096],4096,1,fp);
                  fclose(fp);
                  loop=1;
               }
            }
         }
         if(loop) {
            printf("%s",argv[1]);
            if(loop!=-1)
               printf(".??");
            printf("\n");
            for(x=65535;x>30;x--) {                 /* find checksum table */
               if((buffer[x]==(char)0xf0)&&(buffer[x-2]==(char)0xe0)&&
                     (buffer[x-4]==(char)0xd0)&&(buffer[x-6]==(char)0xc0)&&
                     (buffer[x-8]==(char)0xb0)&&(buffer[x-10]==(char)0xa0)&&
                     (buffer[x-12]==(char)0x90)&&(buffer[x-14]==(char)0x80)&&
                     (buffer[x-16]==0x70)&&(buffer[x-18]==0x60)&&
                     (buffer[x-20]==0x50)&&(buffer[x-22]==0x40)&&
                     (buffer[x-24]==0x30)&&(buffer[x-26]==0x20)&&
                     (buffer[x-28]==0x10)&&(buffer[x-30]==0x00)) {
                  chksumoff=x-30;
                  x=0;
               }
            }
   
            printf("Checksum offset=%X\n",chksumoff);
            
            for(r=0;r<16;r++) {         /* calculate checksum for each ROM */
               sum=0;
               for(x=4096*r;x<4096+4096*r;x++)
                  sum+=buffer[x];
               if(loop!=-1)
                  printf("%s.%02.2d: ",argv[1],r);
               printf("%X000-%XFFF: calc=%02.2hX, known=%02.2hX",r,r,
                  (unsigned char)sum,(unsigned char)buffer[chksumoff+r*2+1]);
               if(sum!=buffer[chksumoff+r*2+1]) {
                  printf("<--- checksum error!");
                  noerror=0;
               }
               printf("\n");
            }
            if(noerror)
               printf("No errors found\n");
         } else
            printf("Can't open file `%s'\n",argv[1]);
         }
   } else
      printf("Usage: `%s <file>'\n",argv[0]);
   free(buffer);
}