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fread.c revision 1.24 
      1 /*	$NetBSD: fread.c,v 1.24 2021/01/31 16:18:22 jdolecek 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 1.24 2021/01/31 16:18:22 jdolecek 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 size_t
     52 fread(void *buf, size_t size, size_t count, FILE *fp)
     53 {
     54 	size_t resid;
     55 	char *p;
     56 	int r;
     57 	size_t total;
     58 
     59 	_DIAGASSERT(fp != NULL);
     60 	/*
     61 	 * The ANSI standard requires a return value of 0 for a count
     62 	 * or a size of 0.  Whilst ANSI imposes no such requirements on
     63 	 * fwrite, the SUSv2 does.
     64 	 */
     65 	if ((resid = count * size) == 0)
     66 		return 0;
     67 
     68 	_DIAGASSERT(buf != NULL);
     69 
     70 	FLOCKFILE(fp);
     71 	if (fp->_r < 0)
     72 		fp->_r = 0;
     73 	total = resid;
     74 	p = buf;
     75 
     76 	/*
     77 	 * If we're unbuffered we know that the buffer in fp is empty so
     78 	 * we can read directly into buf.  This is much faster than a
     79 	 * series of one byte reads into fp->_nbuf.
     80 	 */
     81 	if ((fp->_flags & __SNBF) != 0) {
     82 		while (resid > 0) {
     83 			/* set up the buffer */
     84 			fp->_bf._base = fp->_p = (unsigned char *)p;
     85 			fp->_bf._size = resid;
     86 
     87 			if (__srefill(fp)) {
     88 				/* no more input: return partial result */
     89 				count = (total - resid) / size;
     90 				break;
     91 			}
     92 			p += fp->_r;
     93 			resid -= fp->_r;
     94 		}
     95 
     96 		/* restore the old buffer (see __smakebuf) */
     97 		fp->_bf._base = fp->_p = fp->_nbuf;
     98 		fp->_bf._size = 1;
     99 		fp->_r = 0;
    100 
    101 		FUNLOCKFILE(fp);
    102 		return (count);
    103 	}
    104 
    105 	while (resid > (size_t)(r = fp->_r)) {
    106 		(void)memcpy(p, fp->_p, (size_t)r);
    107 		fp->_p += r;
    108 		/* fp->_r = 0 ... done in __srefill */
    109 		p += r;
    110 		resid -= r;
    111 		if (__srefill(fp)) {
    112 			/* no more input: return partial result */
    113 			FUNLOCKFILE(fp);
    114 			return (total - resid) / size;
    115 		}
    116 	}
    117 	(void)memcpy(p, fp->_p, resid);
    118 
    119 	_DIAGASSERT(__type_fit(int, fp->_r - resid));
    120 	fp->_r -= (int)resid;
    121 	fp->_p += resid;
    122 	FUNLOCKFILE(fp);
    123 	return count;
    124 }
    125