1/*	$NetBSD: fread.c,v 1.27 2024/01/20 14:52:49 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[] = "@(#)fread.c	8.2 (Berkeley) 12/11/93";
39#else
40__RCSID("$NetBSD: fread.c,v 1.27 2024/01/20 14:52:49 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 <string.h>
48#include "reentrant.h"
49#include "local.h"
50
51#define MUL_NO_OVERFLOW	(1UL << (sizeof(size_t) * 4))
52
53size_t
54fread(void *buf, size_t size, size_t count, FILE *fp)
55{
56	size_t resid;
57	char *p;
58	int r;
59	size_t total;
60
61	_DIAGASSERT(fp != NULL);
62
63	/*
64	 * Extension:  Catch integer overflow
65	 */
66	if ((size >= MUL_NO_OVERFLOW || count >= MUL_NO_OVERFLOW) &&
67	    size > 0 && count > SIZE_MAX / size) {
68		errno = EOVERFLOW;
69		fp->_flags |= __SERR;
70		return (0);
71	}
72
73	/*
74	 * The ANSI standard requires a return value of 0 for a count
75	 * or a size of 0.  Whilst ANSI imposes no such requirements on
76	 * fwrite, the SUSv2 does.
77	 */
78	if ((resid = count * size) == 0)
79		return 0;
80
81	_DIAGASSERT(buf != NULL);
82
83	FLOCKFILE(fp);
84	total = resid;
85	p = buf;
86
87	/*
88	 * If we're unbuffered we know that the buffer in fp is empty so
89	 * we can read directly into buf.  This is much faster than a
90	 * series of one byte reads into fp->_nbuf.
91	 */
92	if ((fp->_flags & __SNBF) != 0) {
93		while (resid > 0) {
94			/* set up the buffer */
95			fp->_bf._base = fp->_p = (unsigned char *)p;
96			fp->_bf._size = (int)resid;
97
98			if (__srefill(fp)) {
99				/* no more input: return partial result */
100				count = (total - resid) / size;
101				break;
102			}
103			p += fp->_r;
104			resid -= fp->_r;
105		}
106
107		/* restore the old buffer (see __smakebuf) */
108		fp->_bf._base = fp->_p = fp->_nbuf;
109		fp->_bf._size = 1;
110		fp->_r = 0;
111
112		FUNLOCKFILE(fp);
113		return (count);
114	}
115
116	if (fp->_r <= 0) {
117		/* Nothing to read on enter, refill the buffers. */
118		goto refill;
119	}
120
121	while (resid > (size_t)(r = fp->_r)) {
122		(void)memcpy(p, fp->_p, (size_t)r);
123		fp->_p += r;
124		/* fp->_r = 0 ... done in __srefill */
125		p += r;
126		resid -= r;
127refill:
128		if (__srefill(fp)) {
129			/* no more input: return partial result */
130			FUNLOCKFILE(fp);
131			return (total - resid) / size;
132		}
133	}
134	(void)memcpy(p, fp->_p, resid);
135
136	_DIAGASSERT(__type_fit(int, fp->_r - resid));
137	fp->_r -= (int)resid;
138	fp->_p += resid;
139	FUNLOCKFILE(fp);
140	return count;
141}
142