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sfpeek.c

/***********************************************************************
*                                                                      *
*               This software is part of the ast package               *
*                  Copyright (c) 1985-2006 AT&T Corp.                  *
*                      and is licensed under the                       *
*                  Common Public License, Version 1.0                  *
*                            by AT&T Corp.                             *
*                                                                      *
*                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"

/*    Safe access to the internal stream buffer.
**    This function is obsolete. sfreserve() should be used.
**
**    Written by Kiem-Phong Vo (06/27/90).
*/

#if _BLD_sfio && defined(__EXPORT__)
#define extern    __EXPORT__
#endif

#if __STD_C
extern ssize_t sfpeek(reg Sfio_t* f, Void_t** bp, reg size_t size)
#else
extern ssize_t sfpeek(f,bp,size)
reg Sfio_t* f;    /* file to peek */
Void_t**    bp;   /* start of data area */
reg size_t  size; /* size of peek */
#endif
{     reg ssize_t n, sz;
      reg int           mode;

      /* query for the extent of the remainder of the buffer */
      if((sz = size) == 0 || !bp)
      {     if(f->mode&SF_INIT)
                  (void)_sfmode(f,0,0);

            if((f->flags&SF_RDWRSTR) == SF_RDWRSTR)
            {     SFSTRSIZE(f);
                  n = (f->data+f->here) - f->next;
            }
            else  n = f->endb - f->next;

            if(!bp)
                  return n;
            else if(n > 0)    /* size == 0 */
            {     *bp = (Void_t*)f->next;
                  return 0;
            }
            /* else fall down and fill buffer */
      }

      if(!(mode = f->flags&SF_READ) )
            mode = SF_WRITE;
      if((int)f->mode != mode && _sfmode(f,mode,0) < 0)
            return -1;

      *bp = sfreserve(f, sz <= 0 ? 0 : sz > f->size ? f->size : sz, 0);

      if(*bp && sz >= 0)
            return sz;

      if((n = sfvalue(f)) > 0)
      {     *bp = (Void_t*)f->next;
            if(sz < 0)
            {     f->mode |= SF_PEEK;
                  f->endr = f->endw = f->data;
            }
            else
            {     if(sz > n)
                        sz = n;
                  f->next += sz;
            }
      }

      return (sz >= 0 && n >= sz) ? sz : n;
}

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