/*
 * regsub @(#)regsub.c	1.3 of 2 April 86 
 *
 * Copyright (c) 1986 by University of Toronto. Written by Henry Spencer.  Not
 * derived from licensed software. 
 *
 * Permission is granted to anyone to use this software for any purpose on any
 * computer system, and to redistribute it freely, subject to the following
 * restrictions: 
 *
 * 1. The author is not responsible for the consequences of use of this
 * software, no matter how awful, even if they arise from defects in it. 
 *
 * 2. The origin of this software must not be misrepresented, either by explicit
 * claim or by omission. 
 *
 * 3. Altered versions must be plainly marked as such, and must not be
 * misrepresented as being the original software. 
 */
#include <stdio.h>
#ifdef AMIGA
#include "regexp.h"
#else
#include <regexp.h>
#endif
#include "regmagic.h"

#ifndef CHARBITS
#define	UCHARAT(p)	((int)*(unsigned char *)(p))
#else
#define	UCHARAT(p)	((int)*(p)&CHARBITS)
#endif

/*
 * - regsub - perform substitutions after a regexp match 
 */
void
regsub(prog, source, dest)
    regexp         *prog;
    char           *source;
    char           *dest;
{
    register char  *src;
    register char  *dst;
    register char   c;
    register int    no;
    register int    len;
    extern char    *strncpy();

    if (prog == NULL || source == NULL || dest == NULL) {
	regerror("NULL parm to regsub");
	return;
    }
    if (UCHARAT(prog->program) != MAGIC) {
	regerror("damaged regexp fed to regsub");
	return;
    }
    src = source;
    dst = dest;
    while ((c = *src++) != '\0') {
	if (c == '&')
	    no = 0;
	else if (c == '\\' && '0' <= *src && *src <= '9')
	    no = *src++ - '0';
	else
	    no = -1;

	if (no < 0) {		/* Ordinary character. */
	    if (c == '\\' && (*src == '\\' || *src == '&'))
		c = *src++;
	    *dst++ = c;
	} else if (prog->startp[no] != NULL && prog->endp[no] != NULL) {
	    len = prog->endp[no] - prog->startp[no];
	    (void) strncpy(dst, prog->startp[no], len);
	    dst += len;
	    if (len != 0 && *(dst - 1) == '\0') {	/* strncpy hit NUL. */
		regerror("damaged match string");
		return;
	    }
	}
    }
    *dst++ = '\0';
}