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74 lines
1.3 KiB
C
74 lines
1.3 KiB
C
#include <sys/types.h>
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#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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long v, w, x, y, z;
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uiolen n;
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FILE *f;
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f__curunit = b = &f__units[a->aunit]; /* curunit for error messages */
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if (f__init & 2)
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f__fatal (131, "I/O recursion");
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if(a->aunit >= MXUNIT || a->aunit < 0)
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err(a->aerr,101,"backspace");
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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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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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f = b->ufd; /* may have changed in t_runc() */
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if(b->url>0)
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{
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x=ftell(f);
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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(f,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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{ fseek(f,-(long)sizeof(uiolen),SEEK_CUR);
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fread((char *)&n,sizeof(uiolen),1,f);
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fseek(f,-(long)n-2*sizeof(uiolen),SEEK_CUR);
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return(0);
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}
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w = x = ftell(f);
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z = 0;
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loop:
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while(x) {
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x -= x < 64 ? x : 64;
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fseek(f,x,SEEK_SET);
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for(y = x; y < w; y++) {
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if (getc(f) != '\n')
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continue;
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v = ftell(f);
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if (v == w) {
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if (z)
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goto break2;
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goto loop;
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}
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z = v;
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}
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err(a->aerr,(EOF),"backspace");
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}
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break2:
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fseek(f, z, SEEK_SET);
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return 0;
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}
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