/*      $OpenBSD: ungetc.c,v 1.15 2016/09/21 04:38:56 guenther 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 <stdlib.h>
#include <string.h>
#include "local.h"

static int __submore(FILE *);
/*
 * 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;

        if (_UB(fp)._base == fp->_ubuf) {
                /*
                 * Get a new buffer (rather than expanding the old one).
                 */
                if ((p = malloc(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 = reallocarray(_UB(fp)._base, i, 2);
        if (p == NULL)
                return (EOF);
        /* no overlap (hence can use memcpy) because we doubled the size */
        (void)memcpy(p + i, p, i);
        fp->_p = p + i;
        _UB(fp)._base = p;
        _UB(fp)._size = i * 2;
        return (0);
}

int
ungetc(int c, FILE *fp)
{
        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) {
error:                  FUNLOCKFILE(fp);
                        return (EOF);
                }
                if (fp->_flags & __SWR) {
                        if (__sflush(fp))
                                goto error;
                        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))
                        goto error;
                *--fp->_p = c;
inc_ret:        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--;
                goto inc_ret;
        }

        /*
         * 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);
}
DEF_STRONG(ungetc);