libf2c/libI77/backspace.c

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