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Annotation of 43BSD/usr.lib/libI77/backspace.c, revision 1.1.1.1

1.1       root        1: /*
                      2:  * Copyright (c) 1980 Regents of the University of California.
                      3:  * All rights reserved.  The Berkeley software License Agreement
                      4:  * specifies the terms and conditions for redistribution.
                      5:  *
                      6:  *     @(#)backspace.c 5.2     7/30/85
                      7:  */
                      8: 
                      9: /*
                     10:  * Backspace records
                     11:  */
                     12: 
                     13: #include "fio.h"
                     14: 
                     15: static char    bksp[]  = "backspace";
                     16: char   last_char();
                     17: 
                     18: f_back(a)
                     19: alist  *a;
                     20: {      unit *b;
                     21:        int n,i;
                     22:        long x,y;
                     23: 
                     24:        lfname = NULL;
                     25:        elist = NO;
                     26:        external = YES;
                     27:        errflag = a->aerr;
                     28:        lunit = a->aunit;
                     29:        if (not_legal(lunit))
                     30:                err(errflag, F_ERUNIT, bksp)
                     31:        b= &units[lunit];
                     32:        if(!b->ufd) return(OK);
                     33:        lfname = b->ufnm;
                     34:        if(b->uend)
                     35:        {       b->uend = NO;
                     36:                clearerr(b->ufd);
                     37:                return(OK);
                     38:        }
                     39:        if((x = ftell(b->ufd)) == 0)
                     40:                return(OK);
                     41:        if(!b->useek)
                     42:                err(errflag, F_ERNOBKSP, bksp)
                     43:        if(b->uwrt && (n = t_runc(b, errflag, bksp)))   /* sets 'reading' */
                     44:                return(n);
                     45:        if(b->url)              /* direct access, purely academic */
                     46:        {       y = x%(long)b->url;
                     47:                x -= y?y:b->url;
                     48:                fseek(b->ufd,x,0);
                     49:                return(OK);
                     50:        }
                     51:        if(!b->ufmt)            /* unformatted sequential */
                     52:        {       fseek(b->ufd,-(long)sizeof(int),1);
                     53:                fread((char *)&n,sizeof(int),1,b->ufd);
                     54:                fseek(b->ufd,-(long)n-2*sizeof(int),1);
                     55:                return(OK);
                     56:        }
                     57:        if(x == 1)                      /* formatted sequential */
                     58:        {       rewind(b->ufd);
                     59:                return(OK);
                     60:        }
                     61:        while (last_char(b->ufd) != '\n')       /* slow but simple */
                     62:                ;
                     63:        return(OK);
                     64: }

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