stdio/FreeBSD/ungetc.c

   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  * 4. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 #if defined(LIBC_SCCS) && !defined(lint)
  34 static char sccsid[] = "@(#)ungetc.c    8.2 (Berkeley) 11/3/93";
  35 #endif /* LIBC_SCCS and not lint */
  36 #include <sys/cdefs.h>
  37 __FBSDID("$FreeBSD: src/lib/libc/stdio/ungetc.c,v 1.18 2008/04/17 22:17:54 jhb Exp $");
  38
  39 #include "namespace.h"
  40 #include <stdio.h>
  41 #include <stdlib.h>
  42 #include <string.h>
  43 #include "un-namespace.h"
  44 #include "local.h"
  45 #include "libc_private.h"
  46
  47 static int __submore(FILE *);
  48
  49 /*
  50  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
  51  * the buffer moves, so that it points the same distance from the end,
  52  * and move the bytes in the buffer around as necessary so that they
  53  * are all at the end (stack-style).
  54  */
  55 static int
  56 __submore(FILE *fp)
  57 {
  58         int i;
  59         unsigned char *p;
  60
  61         if (fp->_ub._base == fp->_ubuf) {
  62                 /*
  63                  * Get a new buffer (rather than expanding the old one).
  64                  */
  65                 if ((p = malloc((size_t)BUFSIZ)) == NULL)
  66                         return (EOF);
  67                 fp->_ub._base = p;
  68                 fp->_ub._size = BUFSIZ;
  69                 p += BUFSIZ - sizeof(fp->_ubuf);
  70                 for (i = sizeof(fp->_ubuf); --i >= 0;)
  71                         p[i] = fp->_ubuf[i];
  72                 fp->_p = p;
  73                 return (0);
  74         }
  75         i = fp->_ub._size;
  76         p = realloc(fp->_ub._base, (size_t)(i << 1));
  77         if (p == NULL)
  78                 return (EOF);
  79         /* no overlap (hence can use memcpy) because we doubled the size */
  80         (void)memcpy((void *)(p + i), (void *)p, (size_t)i);
  81         fp->_p = p + i;
  82         fp->_ub._base = p;
  83         fp->_ub._size = i << 1;
  84         return (0);
  85 }
  86
  87 /*
  88  * MT-safe version
  89  */
  90 int
  91 ungetc(int c, FILE *fp)
  92 {
  93         int ret;
  94
  95         if (!__sdidinit)
  96                 __sinit();
  97         FLOCKFILE(fp);
  98         ORIENT(fp, -1);
  99         ret = __ungetc(c, fp);
 100         FUNLOCKFILE(fp);
 101         return (ret);
 102 }
 103
 104 /*
 105  * Non-MT-safe version
 106  */
 107 int
 108 __ungetc(int c, FILE *fp)
 109 {
 110
 111         if (c == EOF)
 112                 return (EOF);
 113         if ((fp->_flags & __SRD) == 0) {
 114                 /*
 115                  * Not already reading: no good unless reading-and-writing.
 116                  * Otherwise, flush any current write stuff.
 117                  */
 118                 if ((fp->_flags & __SRW) == 0)
 119                         return (EOF);
 120                 if (fp->_flags & __SWR) {
 121                         if (__sflush(fp))
 122                                 return (EOF);
 123                         fp->_flags &= ~__SWR;
 124                         fp->_w = 0;
 125                         fp->_lbfsize = 0;
 126                 }
 127                 fp->_flags |= __SRD;
 128         }
 129         c = (unsigned char)c;
 130
 131         /*
 132          * If we are in the middle of ungetc'ing, just continue.
 133          * This may require expanding the current ungetc buffer.
 134          */
 135         if (HASUB(fp)) {
 136                 if (fp->_r >= fp->_ub._size && __submore(fp))
 137                         return (EOF);
 138                 *--fp->_p = c;
 139                 fp->_r++;
 140                 return (c);
 141         }
 142         fp->_flags &= ~__SEOF;
 143
 144         /*
 145          * If we can handle this by simply backing up, do so,
 146          * but never replace the original character.
 147          * (This makes sscanf() work when scanning `const' data.)
 148          */
 149         if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
 150             fp->_p[-1] == c) {
 151                 fp->_p--;
 152                 fp->_r++;
 153                 return (c);
 154         }
 155
 156         /*
 157          * Create an ungetc buffer.
 158          * Initially, we will use the `reserve' buffer.
 159          */
 160         fp->_ur = fp->_r;
 161         fp->_up = fp->_p;
 162         fp->_ub._base = fp->_ubuf;
 163         fp->_ub._size = sizeof(fp->_ubuf);
 164         fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
 165         fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
 166         fp->_r = 1;
 167         return (c);
 168 }