63 lines
1.2 KiB
C
63 lines
1.2 KiB
C
#include "f2c.h"
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#include "fio.h"
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integer f_back(a) alist *a;
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{ unit *b;
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int n,i;
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long x;
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char buf[32];
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if(a->aunit >= MXUNIT || a->aunit < 0)
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err(a->aerr,101,"backspace")
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b= &units[a->aunit];
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if(b->useek==0) err(a->aerr,106,"backspace")
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if(b->ufd==NULL) {
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fk_open(1, 1, a->aunit);
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return(0);
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}
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if(b->uend==1)
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{ b->uend=0;
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return(0);
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}
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if(b->uwrt) {
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(void) t_runc(a);
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if (nowreading(b))
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err(a->aerr,errno,"backspace")
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}
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if(b->url>0)
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{ long y;
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x=ftell(b->ufd);
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y = x % b->url;
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if(y == 0) x--;
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x /= b->url;
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x *= b->url;
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(void) fseek(b->ufd,x,SEEK_SET);
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return(0);
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}
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if(b->ufmt==0)
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{ (void) fseek(b->ufd,-(long)sizeof(int),SEEK_CUR);
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(void) fread((char *)&n,sizeof(int),1,b->ufd);
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(void) fseek(b->ufd,-(long)n-2*sizeof(int),SEEK_CUR);
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return(0);
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}
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for(;;)
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{ long y;
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y = x=ftell(b->ufd);
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if(x<sizeof(buf)) x=0;
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else x -= sizeof(buf);
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(void) fseek(b->ufd,x,SEEK_SET);
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n=fread(buf,1,(int)(y-x), b->ufd);
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for(i=n-2;i>=0;i--)
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{
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if(buf[i]!='\n') continue;
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(void) fseek(b->ufd,(long)(i+1-n),SEEK_CUR);
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return(0);
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}
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if(x==0)
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{
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(void) fseek(b->ufd, 0L, SEEK_SET);
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return(0);
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}
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else if(n<=0) err(a->aerr,(EOF),"backspace")
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(void) fseek(b->ufd, x, SEEK_SET);
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}
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}
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