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
38 static 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
53 size_t
fread(void * buf,size_t size,size_t count,FILE * fp)54 fread(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;
127 refill:
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