/*  UNHEX.C - Program to translate a hex file from standard input
 *  into an 8-bit binary file on standard output.
 *  Christine M. Gianone, CUCCA, October 1986.
 *
 *  Modified - Evan Arnerich, ITT/FSC, January 1993
 *      added arguments for in/out file specs
 */
#include <stdio.h>                    /* Include this for EOF symbol */

char a, b;                            /* High and low hex nibbles */

/* Main program reads each hex digit pair and outputs the 8-bit byte. */

main(argc, argv) int argc; char *argv[]; {

    FILE *in_fp, *out_fp;

    if ((in_fp = fopen(argv[1], "r")) == NULL) {
        printf("error opening %s\n", argv[1]);
        exit(1);
    }
    if ((out_fp = fopen(argv[2], "w")) == NULL) {
        printf("error opening %s\n", argv[2]);
        exit(1);
    }
     while ((a = getc(in_fp)) != EOF) {  /* Read first hex digit */
        if (a == '\n')                /* Ignore line terminators */
          continue;
        if ((b = getc(in_fp)) == EOF)   /* Read second hex digit */
          break;
        putc( ((decode(a) * 16) & 0xF0) + (decode(b) & 0xF), out_fp );
    }
    fclose(in_fp);
    fclose(out_fp);
    exit(0);                          /* Done */
}
decode(x) char x; {                   /* Function to decode a hex character */
    if (x >= '0' && x <= '9')         /* 0-9 is offset by hex 30 */
      return (x - 0x30);
    else if (x >= 'A' && x <= 'F')    /* A-F offset by hex 37 */
      return(x - 0x37);
    else {                            /* Otherwise, an illegal hex digit */
        fprintf(stderr,"Input is not in legal hex format\n");
        exit(1);
    }
}