1/*	$NetBSD: ungetc.c,v 1.14 2003/08/07 16:43:34 agc Exp $	*/
2
3/*-
4 * Copyright (c) 1990, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Chris Torek.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#include <sys/cdefs.h>
36#if defined(LIBC_SCCS) && !defined(lint)
37#if 0
38static char sccsid[] = "@(#)ungetc.c	8.2 (Berkeley) 11/3/93";
39#else
40__RCSID("$NetBSD: ungetc.c,v 1.14 2003/08/07 16:43:34 agc Exp $");
41#endif
42#endif /* LIBC_SCCS and not lint */
43
44#include <assert.h>
45#include <errno.h>
46#include <stdio.h>
47#include <stdlib.h>
48#include <string.h>
49#include "reentrant.h"
50#include "local.h"
51
52static int __submore __P((FILE *));
53/*
54 * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
55 * the buffer moves, so that it points the same distance from the end,
56 * and move the bytes in the buffer around as necessary so that they
57 * are all at the end (stack-style).
58 */
59static int
60__submore(fp)
61	FILE *fp;
62{
63	int i;
64	unsigned char *p;
65
66	_DIAGASSERT(fp != NULL);
67
68	if (_UB(fp)._base == fp->_ubuf) {
69		/*
70		 * Get a new buffer (rather than expanding the old one).
71		 */
72		if ((p = malloc((size_t)BUFSIZ)) == NULL)
73			return (EOF);
74		_UB(fp)._base = p;
75		_UB(fp)._size = BUFSIZ;
76		p += BUFSIZ - sizeof(fp->_ubuf);
77		for (i = sizeof(fp->_ubuf); --i >= 0;)
78			p[i] = fp->_ubuf[i];
79		fp->_p = p;
80		return (0);
81	}
82	i = _UB(fp)._size;
83	p = realloc(_UB(fp)._base, (size_t)(i << 1));
84	if (p == NULL)
85		return (EOF);
86	/* no overlap (hence can use memcpy) because we doubled the size */
87	(void)memcpy((p + i), p, (size_t)i);
88	fp->_p = p + i;
89	_UB(fp)._base = p;
90	_UB(fp)._size = i << 1;
91	return (0);
92}
93
94int
95ungetc(c, fp)
96	int c;
97	FILE *fp;
98{
99
100	_DIAGASSERT(fp != NULL);
101
102	if (c == EOF)
103		return (EOF);
104	if (!__sdidinit)
105		__sinit();
106	FLOCKFILE(fp);
107	_SET_ORIENTATION(fp, -1);
108	if ((fp->_flags & __SRD) == 0) {
109		/*
110		 * Not already reading: no good unless reading-and-writing.
111		 * Otherwise, flush any current write stuff.
112		 */
113		if ((fp->_flags & __SRW) == 0) {
114			FUNLOCKFILE(fp);
115			return (EOF);
116		}
117		if (fp->_flags & __SWR) {
118			if (__sflush(fp)) {
119				FUNLOCKFILE(fp);
120				return (EOF);
121			}
122			fp->_flags &= ~__SWR;
123			fp->_w = 0;
124			fp->_lbfsize = 0;
125		}
126		fp->_flags |= __SRD;
127	}
128	c = (unsigned char)c;
129
130	/*
131	 * If we are in the middle of ungetc'ing, just continue.
132	 * This may require expanding the current ungetc buffer.
133	 */
134	if (HASUB(fp)) {
135		if (fp->_r >= _UB(fp)._size && __submore(fp)) {
136			FUNLOCKFILE(fp);
137			return (EOF);
138		}
139		*--fp->_p = c;
140		fp->_r++;
141		FUNLOCKFILE(fp);
142		return (c);
143	}
144	fp->_flags &= ~__SEOF;
145
146	/*
147	 * If we can handle this by simply backing up, do so,
148	 * but never replace the original character.
149	 * (This makes sscanf() work when scanning `const' data.)
150	 */
151	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
152	    fp->_p[-1] == c) {
153		fp->_p--;
154		fp->_r++;
155		FUNLOCKFILE(fp);
156		return (c);
157	}
158
159	/*
160	 * Create an ungetc buffer.
161	 * Initially, we will use the `reserve' buffer.
162	 */
163	fp->_ur = fp->_r;
164	fp->_up = fp->_p;
165	_UB(fp)._base = fp->_ubuf;
166	_UB(fp)._size = sizeof(fp->_ubuf);
167	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
168	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
169	fp->_r = 1;
170	FUNLOCKFILE(fp);
171	return (c);
172}
173