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ungetc.c revision 1.5 
      1 /*	$NetBSD: ungetc.c,v 1.5 1996/03/29 23:29:27 jtc 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. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *	This product includes software developed by the University of
     21  *	California, Berkeley and its contributors.
     22  * 4. Neither the name of the University nor the names of its contributors
     23  *    may be used to endorse or promote products derived from this software
     24  *    without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     36  * SUCH DAMAGE.
     37  */
     38 
     39 #if defined(LIBC_SCCS) && !defined(lint)
     40 #if 0
     41 static char sccsid[] = "@(#)ungetc.c	8.2 (Berkeley) 11/3/93";
     42 #endif
     43 static char rcsid[] = "$NetBSD: ungetc.c,v 1.5 1996/03/29 23:29:27 jtc Exp $";
     44 #endif /* LIBC_SCCS and not lint */
     45 
     46 #include <stdio.h>
     47 #include <stdlib.h>
     48 #include <string.h>
     49 #include "local.h"
     50 
     51 /*
     52  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
     53  * the buffer moves, so that it points the same distance from the end,
     54  * and move the bytes in the buffer around as necessary so that they
     55  * are all at the end (stack-style).
     56  */
     57 static int
     58 __submore(fp)
     59 	register FILE *fp;
     60 {
     61 	register int i;
     62 	register unsigned char *p;
     63 
     64 	if (fp->_ub._base == fp->_ubuf) {
     65 		/*
     66 		 * Get a new buffer (rather than expanding the old one).
     67 		 */
     68 		if ((p = malloc((size_t)BUFSIZ)) == NULL)
     69 			return (EOF);
     70 		fp->_ub._base = p;
     71 		fp->_ub._size = BUFSIZ;
     72 		p += BUFSIZ - sizeof(fp->_ubuf);
     73 		for (i = sizeof(fp->_ubuf); --i >= 0;)
     74 			p[i] = fp->_ubuf[i];
     75 		fp->_p = p;
     76 		return (0);
     77 	}
     78 	i = fp->_ub._size;
     79 	p = realloc(fp->_ub._base, i << 1);
     80 	if (p == NULL)
     81 		return (EOF);
     82 	/* no overlap (hence can use memcpy) because we doubled the size */
     83 	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
     84 	fp->_p = p + i;
     85 	fp->_ub._base = p;
     86 	fp->_ub._size = i << 1;
     87 	return (0);
     88 }
     89 
     90 int
     91 ungetc(c, fp)
     92 	int c;
     93 	register FILE *fp;
     94 {
     95 	if (c == EOF)
     96 		return (EOF);
     97 	if (!__sdidinit)
     98 		__sinit();
     99 	if ((fp->_flags & __SRD) == 0) {
    100 		/*
    101 		 * Not already reading: no good unless reading-and-writing.
    102 		 * Otherwise, flush any current write stuff.
    103 		 */
    104 		if ((fp->_flags & __SRW) == 0)
    105 			return (EOF);
    106 		if (fp->_flags & __SWR) {
    107 			if (__sflush(fp))
    108 				return (EOF);
    109 			fp->_flags &= ~__SWR;
    110 			fp->_w = 0;
    111 			fp->_lbfsize = 0;
    112 		}
    113 		fp->_flags |= __SRD;
    114 	}
    115 	c = (unsigned char)c;
    116 
    117 	/*
    118 	 * If we are in the middle of ungetc'ing, just continue.
    119 	 * This may require expanding the current ungetc buffer.
    120 	 */
    121 	if (HASUB(fp)) {
    122 		if (fp->_r >= fp->_ub._size && __submore(fp))
    123 			return (EOF);
    124 		*--fp->_p = c;
    125 		fp->_r++;
    126 		return (c);
    127 	}
    128 	fp->_flags &= ~__SEOF;
    129 
    130 	/*
    131 	 * If we can handle this by simply backing up, do so,
    132 	 * but never replace the original character.
    133 	 * (This makes sscanf() work when scanning `const' data.)
    134 	 */
    135 	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
    136 	    fp->_p[-1] == c) {
    137 		fp->_p--;
    138 		fp->_r++;
    139 		return (c);
    140 	}
    141 
    142 	/*
    143 	 * Create an ungetc buffer.
    144 	 * Initially, we will use the `reserve' buffer.
    145 	 */
    146 	fp->_ur = fp->_r;
    147 	fp->_up = fp->_p;
    148 	fp->_ub._base = fp->_ubuf;
    149 	fp->_ub._size = sizeof(fp->_ubuf);
    150 	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
    151 	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
    152 	fp->_r = 1;
    153 	return (c);
    154 }
    155