1/*	$NetBSD: ungetc.c,v 1.16 2009/10/25 20:44:13 christos 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 1.16 2009/10/25 20:44:13 christos 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
52/*
53 * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
54 * the buffer moves, so that it points the same distance from the end,
55 * and move the bytes in the buffer around as necessary so that they
56 * are all at the end (stack-style).
57 */
58static int
59__submore(FILE *fp)
60{
61	int i;
62	unsigned char *p;
63
64	_DIAGASSERT(fp != NULL);
65
66	if (_UB(fp)._base == fp->_ubuf) {
67		/*
68		 * Get a new buffer (rather than expanding the old one).
69		 */
70		if ((p = malloc((size_t)BUFSIZ)) == NULL)
71			return EOF;
72		_UB(fp)._base = p;
73		_UB(fp)._size = BUFSIZ;
74		p += BUFSIZ - sizeof(fp->_ubuf);
75		for (i = sizeof(fp->_ubuf); --i >= 0;)
76			p[i] = fp->_ubuf[i];
77		fp->_p = p;
78		return 0;
79	}
80	i = _UB(fp)._size;
81	p = realloc(_UB(fp)._base, (size_t)(i << 1));
82	if (p == NULL)
83		return EOF;
84	/* no overlap (hence can use memcpy) because we doubled the size */
85	(void)memcpy((p + i), p, (size_t)i);
86	fp->_p = p + i;
87	_UB(fp)._base = p;
88	_UB(fp)._size = i << 1;
89	return 0;
90}
91
92int
93ungetc(int c, FILE *fp)
94{
95
96	_DIAGASSERT(fp != NULL);
97
98	if (c == EOF)
99		return EOF;
100	if (!__sdidinit)
101		__sinit();
102	FLOCKFILE(fp);
103	_SET_ORIENTATION(fp, -1);
104	if ((fp->_flags & __SRD) == 0) {
105		/*
106		 * Not already reading: no good unless reading-and-writing.
107		 * Otherwise, flush any current write stuff.
108		 */
109		if ((fp->_flags & __SRW) == 0) {
110			FUNLOCKFILE(fp);
111			return EOF;
112		}
113		if (fp->_flags & __SWR) {
114			if (__sflush(fp)) {
115				FUNLOCKFILE(fp);
116				return EOF;
117			}
118			fp->_flags &= ~__SWR;
119			fp->_w = 0;
120			fp->_lbfsize = 0;
121		}
122		fp->_flags |= __SRD;
123	}
124	c = (unsigned char)c;
125
126	/*
127	 * If we are in the middle of ungetc'ing, just continue.
128	 * This may require expanding the current ungetc buffer.
129	 */
130	if (HASUB(fp)) {
131		if (fp->_r >= _UB(fp)._size && __submore(fp)) {
132			FUNLOCKFILE(fp);
133			return EOF;
134		}
135		*--fp->_p = c;
136		fp->_r++;
137		FUNLOCKFILE(fp);
138		return c;
139	}
140	fp->_flags &= ~__SEOF;
141
142	/*
143	 * If we can handle this by simply backing up, do so,
144	 * but never replace the original character.
145	 * (This makes sscanf() work when scanning `const' data.)
146	 */
147	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
148	    fp->_p[-1] == c) {
149		fp->_p--;
150		fp->_r++;
151		FUNLOCKFILE(fp);
152		return c;
153	}
154
155	/*
156	 * Create an ungetc buffer.
157	 * Initially, we will use the `reserve' buffer.
158	 */
159	fp->_ur = fp->_r;
160	fp->_up = fp->_p;
161	_UB(fp)._base = fp->_ubuf;
162	_UB(fp)._size = sizeof(fp->_ubuf);
163	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
164	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
165	fp->_r = 1;
166	FUNLOCKFILE(fp);
167	return c;
168}
169