/***
*ungetc.c - unget a character from a stream
*
*	Copyright (c) 1985-1993, Microsoft Corporation. All rights reserved.
*
*Purpose:
*	defines ungetc() - pushes a character back onto an input stream
*
*Revision History:
*	09-02-83  RN	initial version
*	04-16-87  JCR	added support for _IOUNGETC flag
*	08-04-87  JCR	(1) Added _IOSTRG check before setting _IOUNGETC flag.
*			(2) Allow an ugnetc() before a read has occurred (get a
*			buffer (ANSI).	[MSC only]
*	09-28-87  JCR	Corrected _iob2 indexing (now uses _iob_index() macro).
*	11-04-87  JCR	Multi-thread support
*	12-11-87  JCR	Added "_LOAD_DS" to declaration
*	05-25-88  JCR	Allow an ungetc() before read for file opened "r+".
*	05-31-88  PHG	Merged DLL and normal versions
*	06-06-88  JCR	Optimized _iob2 references
*	06-15-88  JCR	Near reference to _iob[] entries; improve REG variables
*	08-25-88  GJF	Don't use FP_OFF() macro for the 386
*	04-11-89  JCR	Removed _IOUNGETC flag, fseek() no longer needs it
*	08-17-89  GJF	Clean up, now specific to OS/2 2.0 (i.e., 386 flat
*			model). Also fixed copyright and indents.
*	02-16-90  GJF	Fixed copyright
*	03-20-90  GJF	Made calling type _CALLTYPE1, added #include
*			<cruntime.h> and removed #include <register.h>.
*	07-23-90  SBM	Replaced <assertm.h> by <assert.h>
*	08-13-90  SBM	Compiles cleanly with -W3
*	10-03-90  GJF	New-style function declarators.
*	11-07-92  SRW	Dont modify buffer if stream opened by sscanf
*	04-26-93  CFW	Wide char enable.
*	04-30-93  CFW	Remove wide char support to ungetwc.c.
*
*******************************************************************************/

#include <cruntime.h>
#include <stdio.h>
#include <file2.h>
#include <assert.h>
#include <internal.h>
#include <os2dll.h>

#ifdef MTHREAD	/* multi-thread; define both ungetc and _lk_ungetc */

/***
*int ungetc(ch, stream) - put a character back onto a stream
*
*Purpose:
*	Guaranteed one char pushback on a stream as long as open for reading.
*	More than one char pushback in a row is not guaranteed, and will fail
*	if it follows an ungetc which pushed the first char in buffer. Failure
*	causes return of EOF.
*
*Entry:
*	char ch - character to push back
*	FILE *stream - stream to push character onto
*
*Exit:
*	returns ch
*	returns EOF if tried to push EOF, stream not opened for reading or
*	or if we have already ungetc'd back to beginning of buffer.
*
*Exceptions:
*
*******************************************************************************/

int _CRTAPI1 ungetc (
	REG2 int ch,
	REG1 FILE *stream
	)
{
	int retval;
	int index;

	assert(stream != NULL);

	index = _iob_index(stream);

	_lock_str(index);

	retval = _ungetc_lk (ch, stream);

	_unlock_str(index);

	return(retval);
}

/***
*_ungetc_lk() -  Ungetc() core routine (locked version)
*
*Purpose:
*	Core ungetc() routine; assumes stream is already locked.
*
*	[See ungetc() above for more info.]
*
*Entry: [See ungetc()]
*
*Exit:	[See ungetc()]
*
*Exceptions:
*
*******************************************************************************/

int _CRTAPI1 _ungetc_lk (
	REG2 int ch,
	FILE *str
	)

{

#else	/* non multi-thread; just define ungetc */

int _CRTAPI1 ungetc (
	REG2 int ch,
	FILE *str
	)

{

#endif	/* rejoin common code */

	REG1 FILE *stream;

	assert(str != NULL);

	/* Init stream pointer and file descriptor */
	stream = str;

	/* Stream must be open for read and can NOT be currently in write mode.
	   Also, ungetc() character cannot be EOF. */

	if (
	      (ch == EOF) ||
	      !(
		(stream->_flag & _IOREAD) ||
		((stream->_flag & _IORW) && !(stream->_flag & _IOWRT))
	       )
	   )
		return(EOF);

	/* If stream is unbuffered, get one. */

	if (stream->_base == NULL)
		_getbuf(stream);

	/* now we know _base != NULL; since file must be buffered */

	if (stream->_ptr == stream->_base) {
		if (stream->_cnt)
			/* my back is against the wall; i've already done
			 * ungetc, and there's no room for this one
			 */
			return(EOF);

		stream->_ptr++;
	}

	if (stream->_flag & _IOSTRG) {
            /* If stream opened by sscanf do not modify buffer */
                if (*--stream->_ptr != (char)ch) {
                        ++stream->_ptr;
                        return(EOF);
                }
        } else
                *--stream->_ptr = (char)ch;

	stream->_cnt++;
	stream->_flag &= ~_IOEOF;
	stream->_flag |= _IOREAD;	/* may already be set */

	return(0xff & ch);
}