lang/fortran/lib/libI77/backspace.c

   1 #include "f2c.h"
   2 #include "fio.h"
   3 integer f_back(a) alist *a;
   4 {       unit *b;
   5         int n,i;
   6         long x;
   7         char buf[32];
   8         if(a->aunit >= MXUNIT || a->aunit < 0)
   9                 err(a->aerr,101,"backspace")
  10         b= &units[a->aunit];
  11         if(b->useek==0) err(a->aerr,106,"backspace")
  12         if(b->ufd==NULL) {
  13                 fk_open(1, 1, a->aunit);
  14                 return(0);
  15                 }
  16         if(b->uend==1)
  17         {       b->uend=0;
  18                 return(0);
  19         }
  20         if(b->uwrt) {
  21                 (void) t_runc(a);
  22                 if (nowreading(b))
  23                         err(a->aerr,errno,"backspace")
  24                 }
  25         if(b->url>0)
  26         {       long y;
  27                 x=ftell(b->ufd);
  28                 y = x % b->url;
  29                 if(y == 0) x--;
  30                 x /= b->url;
  31                 x *= b->url;
  32                 (void) fseek(b->ufd,x,SEEK_SET);
  33                 return(0);
  34         }
  35
  36         if(b->ufmt==0)
  37         {       (void) fseek(b->ufd,-(long)sizeof(int),SEEK_CUR);
  38                 (void) fread((char *)&n,sizeof(int),1,b->ufd);
  39                 (void) fseek(b->ufd,-(long)n-2*sizeof(int),SEEK_CUR);
  40                 return(0);
  41         }
  42         for(;;)
  43         {       long y;
  44                 y = x=ftell(b->ufd);
  45                 if(x<sizeof(buf)) x=0;
  46                 else x -= sizeof(buf);
  47                 (void) fseek(b->ufd,x,SEEK_SET);
  48                 n=fread(buf,1,(int)(y-x), b->ufd);
  49                 for(i=n-2;i>=0;i--)
  50                 {
  51                         if(buf[i]!='\n') continue;
  52                         (void) fseek(b->ufd,(long)(i+1-n),SEEK_CUR);
  53                         return(0);
  54                 }
  55                 if(x==0)
  56                         {
  57                         (void) fseek(b->ufd, 0L, SEEK_SET);
  58                         return(0);
  59                         }
  60                 else if(n<=0) err(a->aerr,(EOF),"backspace")
  61                 (void) fseek(b->ufd, x, SEEK_SET);
  62         }
  63 }