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