/* vi:ts=4:sw=4
 * NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE
 *
 * This is NOT the original regular expression code as written by
 * Henry Spencer. This code has been modified specifically for use
 * with the VIM editor, and should not be used apart from compiling
 * VIM. If you want a good regular expression library, get the
 * original code. The copyright notice that follows is from the
 * original.
 *
 * NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE
 *
 * regsub
 *
 *		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.
 *
 * $Log:		regsub.c,v $
 * Revision 1.2  88/04/28  08:11:25  tony
 * First modification of the regexp library. Added an external variable
 * 'reg_ic' which can be set to indicate that case should be ignored.
 * Added a new parameter to regexec() to indicate that the given string
 * comes from the beginning of a line and is thus eligible to match
 * 'beginning-of-line'.
 *
 */

#include "env.h"

#ifdef	MEGAMAX
overlay "regexp"
#endif

#include <stdio.h>
#include "regexp.h"
#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) {
		emsg("NULL parm to regsub");
		return;
	}
	if (UCHARAT(prog->program) != MAGIC) {
		emsg("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. */
				emsg("damaged match string");
				return;
			}
		}
	}
	*dst = '\0';
}