97 lines
1.7 KiB
C
97 lines
1.7 KiB
C
#include "f2c.h"
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#include "fio.h"
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#ifdef KR_headers
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integer f_back(a) alist *a;
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#else
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integer f_back(alist *a)
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#endif
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{ unit *b;
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int i, n, ndec;
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#ifdef MSDOS
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int j, k;
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long w, z;
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#endif
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long x, y;
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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= &f__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 (f__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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{
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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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#ifdef MSDOS
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w = -1;
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#endif
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for(ndec = 2;; ndec = 1)
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{
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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-ndec;i>=0;i--)
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{
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if(buf[i]!='\n') continue;
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#ifdef MSDOS
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for(j = k = 0; j <= i; j++)
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if (buf[j] == '\n')
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k++;
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fseek(b->ufd,x,SEEK_SET);
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do {
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if (getc(b->ufd) == '\n') {
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--k;
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if ((z = ftell(b->ufd)) >= y) {
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if (w == -1)
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goto break2;
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break;
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}
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w = z;
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}
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} while(k > 0);
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fseek(b->ufd, w, SEEK_SET);
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#else
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fseek(b->ufd,(long)(i+1-n),SEEK_CUR);
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#endif
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return(0);
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}
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#ifdef MSDOS
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break2:
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#endif
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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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