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#include <sys/types.h>
#include "f2c.h"
#include "fio.h"
#ifdef KR_headers
integer f_back(a) alist *a;
#else
integer f_back(alist *a)
#endif
{ unit *b;
long v, w, x, y, z;
uiolen n;
FILE *f;
f__curunit = b = &f__units[a->aunit]; /* curunit for error messages */
if (f__init & 2)
f__fatal (131, "I/O recursion");
if(a->aunit >= MXUNIT || a->aunit < 0)
err(a->aerr,101,"backspace");
if(b->useek==0) err(a->aerr,106,"backspace");
if(b->ufd == NULL) {
fk_open(1, 1, a->aunit);
return(0);
}
if(b->uend==1)
{ b->uend=0;
return(0);
}
if(b->uwrt) {
t_runc(a);
if (f__nowreading(b))
err(a->aerr,errno,"backspace");
}
f = b->ufd; /* may have changed in t_runc() */
if(b->url>0)
{
x=ftell(f);
y = x % b->url;
if(y == 0) x--;
x /= b->url;
x *= b->url;
(void) fseek(f,x,SEEK_SET);
return(0);
}
if(b->ufmt==0)
{ fseek(f,-(long)sizeof(uiolen),SEEK_CUR);
fread((char *)&n,sizeof(uiolen),1,f);
fseek(f,-(long)n-2*sizeof(uiolen),SEEK_CUR);
return(0);
}
w = x = ftell(f);
z = 0;
loop:
while(x) {
x -= x < 64 ? x : 64;
fseek(f,x,SEEK_SET);
for(y = x; y < w; y++) {
if (getc(f) != '\n')
continue;
v = ftell(f);
if (v == w) {
if (z)
goto break2;
goto loop;
}
z = v;
}
err(a->aerr,(EOF),"backspace");
}
break2:
fseek(f, z, SEEK_SET);
return 0;
}
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