/*	$NetBSD: ungetc.c,v 1.17 2012/03/15 18:22:30 christos 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 <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char sccsid[] = "@(#)ungetc.c	8.2 (Berkeley) 11/3/93";
#else
__RCSID("$NetBSD: ungetc.c,v 1.17 2012/03/15 18:22:30 christos Exp $");
#endif
#endif /* LIBC_SCCS and not lint */

#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "reentrant.h"
#include "local.h"

/*
 * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
 * the buffer moves, so that it points the same distance from the end,
 * and move the bytes in the buffer around as necessary so that they
 * are all at the end (stack-style).
 */
static int __submore(FILE *fp) {
  int i;
  unsigned char *p;

  _DIAGASSERT(fp != NULL);

  if (_UB(fp)._base == fp->_ubuf) {
    /*
     * Get a new buffer (rather than expanding the old one).
     */
    if ((p = malloc((size_t)BUFSIZ)) == NULL)
      return EOF;
    _UB(fp)._base = p;
    _UB(fp)._size = BUFSIZ;
    p += BUFSIZ - sizeof(fp->_ubuf);
    for (i = sizeof(fp->_ubuf); --i >= 0;)
      p[i] = fp->_ubuf[i];
    fp->_p = p;
    return 0;
  }
  i = _UB(fp)._size;
  p = realloc(_UB(fp)._base, (size_t)(i << 1));
  if (p == NULL)
    return EOF;
  /* no overlap (hence can use memcpy) because we doubled the size */
  (void)memcpy((p + i), p, (size_t)i);
  fp->_p = p + i;
  _UB(fp)._base = p;
  _UB(fp)._size = i << 1;
  return 0;
}

int ungetc(int c, FILE *fp) {

  _DIAGASSERT(fp != NULL);

  if (c == EOF)
    return EOF;
  if (!__sdidinit)
    __sinit();
  FLOCKFILE(fp);
  _SET_ORIENTATION(fp, -1);
  if ((fp->_flags & __SRD) == 0) {
    /*
     * Not already reading: no good unless reading-and-writing.
     * Otherwise, flush any current write stuff.
     */
    if ((fp->_flags & __SRW) == 0) {
      FUNLOCKFILE(fp);
      return EOF;
    }
    if (fp->_flags & __SWR) {
      if (__sflush(fp)) {
        FUNLOCKFILE(fp);
        return EOF;
      }
      fp->_flags &= ~__SWR;
      fp->_w = 0;
      fp->_lbfsize = 0;
    }
    fp->_flags |= __SRD;
  }
  c = (unsigned char)c;

  /*
   * If we are in the middle of ungetc'ing, just continue.
   * This may require expanding the current ungetc buffer.
   */
  if (HASUB(fp)) {
    if (fp->_r >= _UB(fp)._size && __submore(fp)) {
      FUNLOCKFILE(fp);
      return EOF;
    }
    *--fp->_p = c;
    fp->_r++;
    FUNLOCKFILE(fp);
    return c;
  }
  fp->_flags &= ~__SEOF;

  /*
   * If we can handle this by simply backing up, do so,
   * but never replace the original character.
   * (This makes sscanf() work when scanning `const' data.)
   */
  if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && fp->_p[-1] == c) {
    fp->_p--;
    fp->_r++;
    FUNLOCKFILE(fp);
    return c;
  }

  /*
   * Create an ungetc buffer.
   * Initially, we will use the `reserve' buffer.
   */
  fp->_ur = fp->_r;
  fp->_up = fp->_p;
  _UB(fp)._base = fp->_ubuf;
  _UB(fp)._size = sizeof(fp->_ubuf);
  fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
  fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
  fp->_r = 1;
  FUNLOCKFILE(fp);
  return c;
}
