libf2c/libI77/backspace.c

   1 #include "config.h"
   2 #include <sys/types.h>
   3 #include "f2c.h"
   4 #include "fio.h"
   5 integer
   6 f_back (alist * a)
   7 {
   8   unit *b;
   9   off_t v, w, x, y, z;
  10   uiolen n;
  11   FILE *f;
  12
  13   f__curunit = b = &f__units[a->aunit]; /* curunit for error messages */
  14   if (f__init & 2)
  15     f__fatal (131, "I/O recursion");
  16   if (a->aunit >= MXUNIT || a->aunit < 0)
  17     err (a->aerr, 101, "backspace");
  18   if (b->useek == 0)
  19     err (a->aerr, 106, "backspace");
  20   if (b->ufd == NULL)
  21     {
  22       fk_open (1, 1, a->aunit);
  23       return (0);
  24     }
  25   if (b->uend == 1)
  26     {
  27       b->uend = 0;
  28       return (0);
  29     }
  30   if (b->uwrt)
  31     {
  32       t_runc (a);
  33       if (f__nowreading (b))
  34         err (a->aerr, errno, "backspace");
  35     }
  36   f = b->ufd;                   /* may have changed in t_runc() */
  37   if (b->url > 0)
  38     {
  39       x = FTELL (f);
  40       y = x % b->url;
  41       if (y == 0)
  42         x--;
  43       x /= b->url;
  44       x *= b->url;
  45       FSEEK (f, x, SEEK_SET);
  46       return (0);
  47     }
  48
  49   if (b->ufmt == 0)
  50     {
  51       FSEEK (f, -(off_t) sizeof (uiolen), SEEK_CUR);
  52       fread ((char *) &n, sizeof (uiolen), 1, f);
  53       FSEEK (f, -(off_t) n - 2 * sizeof (uiolen), SEEK_CUR);
  54       return (0);
  55     }
  56   w = x = FTELL (f);
  57   z = 0;
  58 loop:
  59   while (x)
  60     {
  61       x -= x < 64 ? x : 64;
  62       FSEEK (f, x, SEEK_SET);
  63       for (y = x; y < w; y++)
  64         {
  65           if (getc (f) != '\n')
  66             continue;
  67           v = FTELL (f);
  68           if (v == w)
  69             {
  70               if (z)
  71                 goto break2;
  72               goto loop;
  73             }
  74           z = v;
  75         }
  76       err (a->aerr, (EOF), "backspace");
  77     }
  78 break2:
  79   FSEEK (f, z, SEEK_SET);
  80   return 0;
  81 }