BSD 4_2 release

[unix-history] / usr / src / usr.lib / libI77 / backspace.c

/*
char id_backspace[] = "@(#)backspace.c  1.6";
*
* Backspace records
*/

#include "fio.h"

static char     bksp[]  = "backspace";
char    last_char();

f_back(a)
alist   *a;
{       unit *b;
       int n,i;
       long x,y;

       lfname = NULL;
       elist = NO;
       external = YES;
       errflag = a->aerr;
       lunit = a->aunit;
       if (not_legal(lunit))
               err(errflag, F_ERUNIT, bksp)
       b= &units[lunit];
       if(!b->ufd && (n = fk_open(READ, SEQ, FMT, (ftnint)lunit)) )
               err(errflag, n, bksp)
       lfname = b->ufnm;
       if(b->uend)
       {       b->uend = NO;
               clearerr(b->ufd);
               return(OK);
       }
       if((x = ftell(b->ufd)) == 0)
               return(OK);
       if(!b->useek)
               err(errflag, F_ERNOBKSP, bksp)
       if(b->uwrt && (n = t_runc(b, errflag, bksp)))   /* sets 'reading' */
               return(n);
       if(b->url)              /* direct access, purely academic */
       {       y = x%(long)b->url;
               x -= y?y:b->url;
               fseek(b->ufd,x,0);
               return(OK);
       }
       if(!b->ufmt)            /* unformatted sequential */
       {       fseek(b->ufd,-(long)sizeof(int),1);
               fread((char *)&n,sizeof(int),1,b->ufd);
               fseek(b->ufd,-(long)n-2*sizeof(int),1);
               return(OK);
       }
       if(x == 1)                      /* formatted sequential */
       {       rewind(b->ufd);
               return(OK);
       }
       while (last_char(b->ufd) != '\n')       /* slow but simple */
               ;
       return(OK);
}