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fread.c revision 1.1.1.2 
      1 /*-
      2  * Copyright (c) 1990, 1993
      3  *	The Regents of the University of California.  All rights reserved.
      4  *
      5  * This code is derived from software contributed to Berkeley by
      6  * Chris Torek.
      7  *
      8  * Redistribution and use in source and binary forms, with or without
      9  * modification, are permitted provided that the following conditions
     10  * are met:
     11  * 1. Redistributions of source code must retain the above copyright
     12  *    notice, this list of conditions and the following disclaimer.
     13  * 2. Redistributions in binary form must reproduce the above copyright
     14  *    notice, this list of conditions and the following disclaimer in the
     15  *    documentation and/or other materials provided with the distribution.
     16  * 3. All advertising materials mentioning features or use of this software
     17  *    must display the following acknowledgement:
     18  *	This product includes software developed by the University of
     19  *	California, Berkeley and its contributors.
     20  * 4. Neither the name of the University nor the names of its contributors
     21  *    may be used to endorse or promote products derived from this software
     22  *    without specific prior written permission.
     23  *
     24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     34  * SUCH DAMAGE.
     35  */
     36 
     37 #if defined(LIBC_SCCS) && !defined(lint)
     38 static char sccsid[] = "@(#)fread.c	8.2 (Berkeley) 12/11/93";
     39 #endif /* LIBC_SCCS and not lint */
     40 
     41 #include <stdio.h>
     42 #include <string.h>
     43 
     44 size_t
     45 fread(buf, size, count, fp)
     46 	void *buf;
     47 	size_t size, count;
     48 	register FILE *fp;
     49 {
     50 	register size_t resid;
     51 	register char *p;
     52 	register int r;
     53 	size_t total;
     54 
     55 	/*
     56 	 * The ANSI standard requires a return value of 0 for a count
     57 	 * or a size of 0.  Peculiarily, it imposes no such requirements
     58 	 * on fwrite; it only requires fread to be broken.
     59 	 */
     60 	if ((resid = count * size) == 0)
     61 		return (0);
     62 	if (fp->_r < 0)
     63 		fp->_r = 0;
     64 	total = resid;
     65 	p = buf;
     66 	while (resid > (r = fp->_r)) {
     67 		(void)memcpy((void *)p, (void *)fp->_p, (size_t)r);
     68 		fp->_p += r;
     69 		/* fp->_r = 0 ... done in __srefill */
     70 		p += r;
     71 		resid -= r;
     72 		if (__srefill(fp)) {
     73 			/* no more input: return partial result */
     74 			return ((total - resid) / size);
     75 		}
     76 	}
     77 	(void)memcpy((void *)p, (void *)fp->_p, resid);
     78 	fp->_r -= resid;
     79 	fp->_p += resid;
     80 	return (count);
     81 }
     82