/**
 **   xor - exclusive or two files
 ** 
 **  CREATED:  99.08.23  ABS  copied from simple_diff
 **  MODIFIED: 99.09.01  ABS  got working
 **  MODIFIED: 99.09.04  ABS  added skip and self-doc
 **
 **/

#include        "xor.h"

main(argc, argv)
int argc;
char** argv;
{
    /* declare functions */

    double atof();
    char xor();

    /* declare local variables */

    FILE *stream1;
    FILE *stream2;
    char c1, c2;
    int s;
    int stillReading = TRUE;
    int j = 0;
    int n1, n2;

    /* initialize global variables (including parameters) */

    defaultParms();

    parseArgs(argc, argv);

    /* initialize local variables */

    /* open */

    if (Debug != FALSE) {
        fprintf(stdout, "%s: DEBUG: Filename1 = %s\n", argv[0], Filename1);
        fprintf(stdout, "%s: DEBUG: Filename2 = %s\n", argv[0], Filename2);
        }

    stream1 = fopen (Filename1,  "r+b");

    if (stream1 == 0) {
        fprintf(stdout, "%s: ERROR opening file %s\n", argv[0],
            Filename1);
        exit(-1);
        }

    stream2 = fopen (Filename2,  "r+b");

    if (stream2 == 0) {
        fprintf(stdout, "%s: ERROR opening file %s\n", argv[0],
            Filename2);
        exit(-1);
        }

    for (s = 0; s < Skip; s++) {
#ifdef NT
        n2 = fread(&c2, 1, 1, stream2);
#else
        c2 = (char)getc(stream2);
#endif NT
        if (feof(stream2)) {
            fprintf(stdout, "%s: ERROR skip value is longer thsn key file %s\n",
                argv[0], Filename2);
            exit(-1);
            }
        }

    /* read & write */

    while (stillReading) {
        j++;

#ifdef NT
        n1 = fread(&c1, 1, 1, stream1);
        n2 = fread(&c2, 1, 1, stream2);
#else
        c1 = (char)getc(stream1);
        c2 = (char)getc(stream2);
#endif NT

        if (feof(stream1) || feof(stream2)) {
            exit(0);
            }
#ifdef NT
        else if (n1 != 1) {
            fprintf(stdout, "%s: ERROR reading file %s on character %d\n",
                argv[0], Filename1, j);
            exit(-1);
            }
        else if (n2 != 1) {
            fprintf(stdout, "%s: ERROR reading file %s on character %d\n",
                argv[0], Filename2, j);
            exit(-1);
            }
#endif NT

        putchar(xor(c1, c2));

        if (Debug != FALSE && j < 55) {
            fprintf(stdout, "%s: DEBUG: c1 = %c = %d\n", argv[0], (char)c1, c1);
            fprintf(stdout, "%s: DEBUG: c2 = %c = %d\n", argv[0], (char)c2, c2);
            }

        } /* end while */

    if (Debug != FALSE) {
        fprintf(stdout, "%s: DEBUG: j = %d\n", argv[0], j);
        }

    } /* end main */

/*
 *  defaultParms - initialize global variables
 */
defaultParms()
{
    Debug = FALSE;

    Skip = 0;

    } /* end defaultParms() */

/*
 *  parseArgs - parse arguments into global variables
 */
parseArgs(argc, argv)
int argc;
char** argv;
{
    int i;

    for (i = 0; i < argc; i++) {
        if (argv[i][0] == '-') {
            switch (argv[i][1]) {
                case 'f' : strcpy(Filename1, (char *)&argv[++i][0]);
                           break;
                case 'k' : strcpy(Filename2, (char *)&argv[++i][0]);
                           break;
                case 'D' : Debug = TRUE;
                           break;
                case 'h' : help(argv);
                           exit(0);
                           break;
                case 's' : Skip = atoi(&argv[++i][0]);
                           break;
                case 'u' : usage(argv);
                           exit(0);
                           break;
                default:   fprintf(stdout, "%s: ERROR: illegal flag: %s\n",
                               argv[0], argv[i]);
                           usage(argv);
                           exit(0);
                           break;
                } /* end switch */
            } /* end if */
        } /* end for(i) */
    } /* end parseArgs() */

char xor(c1, c2)
char c1;
char c2;
{

    int i;
    char c3;
    char masks[8];

    masks[0] = (char)0x01; /* bit 0 */
    masks[1] = (char)0x02; /* bit 1 */
    masks[2] = (char)0x04; /* bit 2 */
    masks[3] = (char)0x08; /* bit 3 */
    masks[4] = (char)0x10; /* bit 4 */
    masks[5] = (char)0x20; /* bit 5 */
    masks[6] = (char)0x40; /* bit 6 */
    masks[7] = (char)0x80; /* bit 7 */

    c3 = (char)0;

    for (i = 0; i < 8; i++) {
        if (((masks[i] & c1) && !(masks[i] & c2)) ||
            (!(masks[i] & c1) && (masks[i] & c2))) {
            c3 += masks[i];
            }
        }
    return c3;
    }