common/sfio/sfungetc.c

	sfungetc.c revision da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968
/***********************************************************************
*                                                                      *
*               This software is part of the ast package               *
*           Copyright (c) 1985-2007 AT&T Knowledge Ventures            *
*                      and is licensed under the                       *
*                  Common Public License, Version 1.0                  *
*                      by AT&T Knowledge Ventures                      *
*                                                                      *
*                A copy of the License is available at                 *
*            http://www.opensource.org/licenses/cpl1.0.txt             *
*         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
*                                                                      *
*              Information and Software Systems Research               *
*                            AT&T Research                             *
*                           Florham Park NJ                            *
*                                                                      *
*                 Glenn Fowler <gsf@research.att.com>                  *
*                  David Korn <dgk@research.att.com>                   *
*                   Phong Vo <kpv@research.att.com>                    *
*                                                                      *
***********************************************************************/
#include    "sfhdr.h"

/*  Push back one byte to a given SF_READ stream
**
**  Written by Kiem-Phong Vo.
*/
#if __STD_C
static int _uexcept(reg Sfio_t* f, reg int type, Void_t* val, reg Sfdisc_t* disc)
#else
static int _uexcept(f,type,val,disc)
reg Sfio_t  *f;
reg int     type;
Void_t*     val;
reg Sfdisc_t    *disc;
#endif
{
    NOTUSED(val);

    /* hmm! This should never happen */
    if(disc != _Sfudisc)
        return -1;

    /* close the unget stream */
    if(type != SF_CLOSING)
        (void)sfclose((*_Sfstack)(f,NIL(Sfio_t*)));

    return 1;
}

#if __STD_C
int sfungetc(reg Sfio_t* f, reg int c)
#else
int sfungetc(f,c)
reg Sfio_t* f;  /* push back one byte to this stream */
reg int     c;  /* the value to be pushed back */
#endif
{
    reg Sfio_t* uf;

    SFMTXSTART(f, -1)

    if(c < 0 || (f->mode != SF_READ && _sfmode(f,SF_READ,0) < 0))
        SFMTXRETURN(f, -1);
    SFLOCK(f,0);

    /* fast handling of the typical unget */
    if(f->next > f->data && f->next[-1] == (uchar)c)
    {   f->next -= 1;
        goto done;
    }

    /* make a string stream for unget characters */
    if(f->disc != _Sfudisc)
    {   if(!(uf = sfnew(NIL(Sfio_t*),NIL(char*),(size_t)SF_UNBOUND,
                -1,SF_STRING|SF_READ)))
        {   c = -1;
            goto done;
        }
        _Sfudisc->exceptf = _uexcept;
        sfdisc(uf,_Sfudisc);
        SFOPEN(f,0); (void)sfstack(f,uf); SFLOCK(f,0);
    }

    /* space for data */
    if(f->next == f->data)
    {   reg uchar*  data;
        if(f->size < 0)
            f->size = 0;
        if(!(data = (uchar*)malloc(f->size+16)))
        {   c = -1;
            goto done;
        }
        f->flags |= SF_MALLOC;
        if(f->data)
            memcpy((char*)(data+16),(char*)f->data,f->size);
        f->size += 16;
        f->data  = data;
        f->next  = data+16;
        f->endb  = data+f->size;
    }

    *--f->next = (uchar)c;
done:
    SFOPEN(f,0);
    SFMTXRETURN(f, c);
}