diplodocus.org Git - nmh/blob - docs/historical/mh-jun-1982/Extras/libh/fseek.c

   1 #ifdef COMMENT
   2         Proprietary Rand Corporation, 1981.
   3         Further distribution of this software
   4         subject to the terms of the Rand
   5         license agreement.
   6 #endif
   7
   8 #include "/h/stat.h"
   9 #include "/h/iobuf.h"
  10 /* used for input using getc/getw */
  11 /* does equivalent to requested seek */
  12 /* by doing seek by blocks if necessary, */
  13 /* and then adjusting nleft/nextp in iobuf */
  14 /* first arg is iobuf pointer, others are identical to seek or lseek */
  15 struct { int hiword, loword; };
  16 struct { char lobyte, hibyte; };
  17
  18 fseek(bp, offs, dir)
  19 struct iobuf *bp;
  20 {
  21         long loff;
  22
  23         loff = offs;
  24         if (dir%3 == 0) loff.hiword = 0;
  25         return(lfseek(bp, loff, dir));
  26 }
  27
  28 lfseek(abp, aloff, adir)
  29 struct iobuf *abp;
  30 long aloff;
  31 {
  32         register byteoff, blockoff;
  33         long loff;
  34         register struct iobuf *bp;
  35         int dir;
  36         struct inode statb;
  37         long lsize;
  38
  39         bp = abp;
  40         dir = adir;
  41         loff = aloff;
  42
  43         if (dir >= 3) {
  44                 loff =<< 9;
  45                 dir =- 3;
  46         }
  47         switch(dir) {
  48         case 1:
  49                 /* relative seek */
  50                 if (bp->b_nleft >= 0) {
  51                         if (bp->b_nextp) {
  52                                 byteoff = bp->b_nextp-bp->b_buff;
  53                                 loff =+ byteoff;
  54                                 bp->b_nleft =+ byteoff;
  55                         }
  56                         break;
  57                 }
  58                 /* negative nleft means must be at e.o.f */
  59                 /* drop into rel.-to-end seek */
  60         case 2:
  61                 if (fstat(bp->b_fildes, &statb) < 0)
  62                         return(-1);
  63                 lsize.hiword.hibyte = 0;
  64                 lsize.hiword.lobyte = statb.i_size0;
  65                 lsize.loword = statb.i_size1;
  66                 /* adjust loff by size of file */
  67                 loff =+ lsize;
  68                 dir = 0;        /* now have offset rel.-to-beg. */
  69         case 0:
  70                 /* rel.-to-beginning of file seek */
  71                 bp->b_nleft = 0;
  72                 break;
  73         default:
  74                 return(-1);
  75         }
  76
  77         bp->b_nextp = bp->b_buff;
  78         blockoff = loff>>9;
  79         byteoff = loff;
  80         byteoff =& 0777;
  81         if (dir != 1 || blockoff != 0) {
  82                 /* must do the seek */
  83                 if (seek(bp->b_fildes, blockoff, dir+3) < 0)
  84                         return(-1);
  85                 bp->b_nleft = read(bp->b_fildes, &bp->b_buff, 512);
  86         }
  87         bp->b_nleft =- byteoff;
  88         bp->b_nextp =+ byteoff;
  89         retur