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