int
do_trans(TARG,arg)
STR *TARG;
ARG *arg;
{
    register short *tbl;
    register char *s;
    register int matches = 0;
    register int ch;
    register char *send;
    register char *d;
    register int squash = arg[2].arg_len & 1;

    tbl = (short*) arg[2].arg_ptr.arg_cval;
    s = str_get(TARG);
    send = s + TARG->str_cur;
    if (!tbl || !s)
	fatal("panic: do_trans");
#ifdef DEBUGGING
    if (debug & 8) {
	deb("2.TBL\n");
    }
#endif
    if (!arg[2].arg_len) {
	while (s < send) {
	    if ((ch = tbl[*s & 0377]) >= 0) {
		matches++;
		*s = ch;
	    }
	    s++;
	}
    }
    else {
	d = s;
	while (s < send) {
	    if ((ch = tbl[*s & 0377]) >= 0) {
		*d = ch;
		if (matches++ && squash) {
		    if (d[-1] == *d)
			matches--;
		    else
			d++;
		}
		else
		    d++;
	    }
	    else if (ch == -1)		/* -1 is unmapped character */
		*d++ = *s;		/* -2 is delete character */
	    s++;
	}
	matches += send - d;	/* account for disappeared chars */
	*d = '\0';
	TARG->str_cur = d - TARG->str_ptr;
    }
    STABSET(TARG);
    return matches;
}