IABSD.fr/src/lib/libc/stdio/fread.c

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• Author : millert
  Date : 2018-12-16 15:38:29
  Hash : 25b5379d
  Message : Restore the optimization for unbuffered I/O. The buffer needs to be reset before each call to __srefill(). Passes new regress. OK semarie@

• lib/libc/stdio/fread.c

• /*	$OpenBSD: fread.c,v 1.19 2018/12/16 15:38:29 millert Exp $ */
  /*-
   * Copyright (c) 1990, 1993
   *	The Regents of the University of California.  All rights reserved.
   *
   * This code is derived from software contributed to Berkeley by
   * Chris Torek.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   */
  
  #include <stdio.h>
  #include <string.h>
  #include <stdint.h>
  #include <errno.h>
  #include "local.h"
  
  #define MUL_NO_OVERFLOW	(1UL << (sizeof(size_t) * 4))
  
  size_t
  fread(void *buf, size_t size, size_t count, FILE *fp)
  {
  	size_t resid;
  	char *p;
  	int r;
  	size_t total;
  
  	/*
  	 * Extension:  Catch integer overflow
  	 */
  	if ((size >= MUL_NO_OVERFLOW || count >= MUL_NO_OVERFLOW) &&
  	    size > 0 && SIZE_MAX / size < count) {
  		errno = EOVERFLOW;
  		fp->_flags |= __SERR;
  		return (0);
  	}
  
  	/*
  	 * ANSI and SUSv2 require a return value of 0 if size or count are 0.
  	 */
  	if ((resid = count * size) == 0)
  		return (0);
  	FLOCKFILE(fp);
  	_SET_ORIENTATION(fp, -1);
  	if (fp->_r < 0)
  		fp->_r = 0;
  	total = resid;
  	p = buf;
  
  	/*
  	 * If we're unbuffered we know that the buffer in fp is empty so
  	 * we can read directly into buf.  This is much faster than a
  	 * series of one byte reads into fp->_nbuf.
  	 */
  	if ((fp->_flags & __SNBF) != 0 && buf != NULL) {
  		while (resid > 0) {
  			/* set up the buffer */
  			fp->_bf._base = fp->_p = p;
  			fp->_bf._size = resid;
  
  			if (__srefill(fp)) {
  				/* no more input: return partial result */
  				count = (total - resid) / size;
  				break;
  			}
  			p += fp->_r;
  			resid -= fp->_r;
  		}
  
  		/* restore the old buffer (see __smakebuf) */
  		fp->_bf._base = fp->_p = fp->_nbuf;
  		fp->_bf._size = 1;
  		fp->_r = 0;
  
  		FUNLOCKFILE(fp);
  		return (count);
  	}
  
  	while (resid > (r = fp->_r)) {
  		(void)memcpy(p, fp->_p, r);
  		fp->_p += r;
  		/* fp->_r = 0 ... done in __srefill */
  		p += r;
  		resid -= r;
  		if (__srefill(fp)) {
  			/* no more input: return partial result */
  			FUNLOCKFILE(fp);
  			return ((total - resid) / size);
  		}
  	}
  	(void)memcpy(p, fp->_p, resid);
  	fp->_r -= resid;
  	fp->_p += resid;
  	FUNLOCKFILE(fp);
  	return (count);
  }
  DEF_STRONG(fread);