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      1 /*	$OpenBSD: fread.c,v 1.12 2014/05/01 16:40:36 deraadt Exp $ */
      2 /*-
      3  * Copyright (c) 1990, 1993
      4  *	The Regents of the University of California.  All rights reserved.
      5  *
      6  * This code is derived from software contributed to Berkeley by
      7  * Chris Torek.
      8  *
      9  * Redistribution and use in source and binary forms, with or without
     10  * modification, are permitted provided that the following conditions
     11  * are met:
     12  * 1. Redistributions of source code must retain the above copyright
     13  *    notice, this list of conditions and the following disclaimer.
     14  * 2. Redistributions in binary form must reproduce the above copyright
     15  *    notice, this list of conditions and the following disclaimer in the
     16  *    documentation and/or other materials provided with the distribution.
     17  * 3. Neither the name of the University nor the names of its contributors
     18  *    may be used to endorse or promote products derived from this software
     19  *    without specific prior written permission.
     20  *
     21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     31  * SUCH DAMAGE.
     32  */
     33 
     34 #include <stdio.h>
     35 #include <string.h>
     36 #include <stdint.h>
     37 #include <errno.h>
     38 #include "local.h"
     39 
     40 #define MUL_NO_OVERFLOW	(1UL << (sizeof(size_t) * 4))
     41 
     42 size_t
     43 fread(void *buf, size_t size, size_t count, FILE *fp)
     44 {
     45 	size_t resid;
     46 	char *p;
     47 	int r;
     48 	size_t total;
     49 
     50 	/*
     51 	 * Extension:  Catch integer overflow
     52 	 */
     53 	if ((size >= MUL_NO_OVERFLOW || count >= MUL_NO_OVERFLOW) &&
     54 	    size > 0 && SIZE_MAX / size < count) {
     55 		errno = EOVERFLOW;
     56 		fp->_flags |= __SERR;
     57 		return (0);
     58 	}
     59 
     60 	/*
     61 	 * ANSI and SUSv2 require a return value of 0 if size or count are 0.
     62 	 */
     63 	if ((resid = count * size) == 0)
     64 		return (0);
     65 	FLOCKFILE(fp);
     66 	_SET_ORIENTATION(fp, -1);
     67 	if (fp->_r < 0)
     68 		fp->_r = 0;
     69 	total = resid;
     70 	p = buf;
     71 
     72 	// BEGIN android-added
     73 	// Avoid pathological behavior on unbuffered files. OpenBSD
     74 	// will loop reading one byte then memcpying one byte!
     75 	if ((fp->_flags & __SNBF) != 0) {
     76 		// We know if we're unbuffered that our buffer is empty, so
     77 		// we can just read directly.
     78 		while (resid > 0 && (r = (*fp->_read)(fp->_cookie, p, resid)) > 0) {
     79 			p += r;
     80 			resid -= r;
     81 		}
     82 		FUNLOCKFILE(fp);
     83 		return ((total - resid) / size);
     84 	}
     85 	// END android-added
     86 
     87 	while (resid > (size_t)(r = fp->_r)) {
     88 		(void)memcpy((void *)p, (void *)fp->_p, (size_t)r);
     89 		fp->_p += r;
     90 		/* fp->_r = 0 ... done in __srefill */
     91 		p += r;
     92 		resid -= r;
     93 		if (__srefill(fp)) {
     94 			/* no more input: return partial result */
     95 			FUNLOCKFILE(fp);
     96 			return ((total - resid) / size);
     97 		}
     98 	}
     99 	(void)memcpy((void *)p, (void *)fp->_p, resid);
    100 	fp->_r -= resid;
    101 	fp->_p += resid;
    102 	FUNLOCKFILE(fp);
    103 	return (count);
    104 }
    105