cde/programs/dtksh/ksh93/src/lib/libast/sfio/sfpeek.c

   1 /* $XConsortium: sfpeek.c /main/3 1995/11/01 18:32:14 rswiston $ */
   2 /***************************************************************
   3 *                                                              *
   4 *                      AT&T - PROPRIETARY                      *
   5 *                                                              *
   6 *         THIS IS PROPRIETARY SOURCE CODE LICENSED BY          *
   7 *                          AT&T CORP.                          *
   8 *                                                              *
   9 *                Copyright (c) 1995 AT&T Corp.                 *
  10 *                     All Rights Reserved                      *
  11 *                                                              *
  12 *           This software is licensed by AT&T Corp.            *
  13 *       under the terms and conditions of the license in       *
  14 *       http://www.research.att.com/orgs/ssr/book/reuse        *
  15 *                                                              *
  16 *               This software was created by the               *
  17 *           Software Engineering Research Department           *
  18 *                    AT&T Bell Laboratories                    *
  19 *                                                              *
  20 *               For further information contact                *
  21 *                     gsf@research.att.com                     *
  22 *                                                              *
  23 ***************************************************************/
  24 #include        "sfhdr.h"
  25
  26 /*      Safe access to the internal stream buffer.
  27 **      This function is obsolete. sfreserve() should be used.
  28 **
  29 **      Written by Kiem-Phong Vo (06/27/90).
  30 */
  31
  32 #if __STD_C
  33 sfpeek(reg Sfio_t* f, Void_t** bp, reg int size)
  34 #else
  35 sfpeek(f,bp,size)
  36 reg Sfio_t*     f;      /* file to peek */
  37 Void_t**        bp;     /* start of data area */
  38 reg int         size;   /* size of peek */
  39 #endif
  40 {       reg int n;
  41
  42         /* query for the extent of the remainder of the buffer */
  43         if(!bp || size == 0)
  44         {       if(f->mode&SF_INIT)
  45                         (void)_sfmode(f,0,0);
  46
  47                 if((f->flags&SF_RDWRSTR) == SF_RDWRSTR)
  48                 {       SFSTRSIZE(f);
  49                         n = (f->data+f->here) - f->next;
  50                 }
  51                 else    n = f->endb - f->next;
  52
  53                 if(!bp)
  54                         return n;
  55                 else if(n > 0)  /* size == 0 */
  56                 {       *bp = (Void_t*)f->next;
  57                         return 0;
  58                 }
  59                 /* else fall down and fill buffer */
  60         }
  61
  62         if(!(n = f->flags&SF_READ) )
  63                 n = SF_WRITE;
  64         if(f->mode != n && _sfmode(f,n,0) < 0)
  65                 return -1;
  66
  67         *bp = sfreserve(f, size <= 0 ? 0 : size > f->size ? f->size : size, 0);
  68
  69         if(*bp && size >= 0)
  70                 return size;
  71
  72         if((n = sfslen()) > 0)
  73         {       *bp = (Void_t*)f->next;
  74                 if(size < 0)
  75                 {       f->mode |= SF_PEEK;
  76                         f->endr = f->endw = f->data;
  77                 }
  78                 else
  79                 {       if(size > n)
  80                                 size = n;
  81                         f->next += size;
  82                 }
  83         }
  84
  85         return (size >= 0 && n >= size) ? size : n;
  86 }