mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-20 11:11:24 +00:00
99 lines
1.8 KiB
C
99 lines
1.8 KiB
C
#include "f2c.h"
|
|
#include "fio.h"
|
|
#ifdef KR_headers
|
|
integer f_back(a) alist *a;
|
|
#else
|
|
integer f_back(alist *a)
|
|
#endif
|
|
{ unit *b;
|
|
int i, n, ndec;
|
|
#ifdef MSDOS
|
|
int j, k;
|
|
long w, z;
|
|
#endif
|
|
long x, y;
|
|
char buf[32];
|
|
if(a->aunit >= MXUNIT || a->aunit < 0)
|
|
err(a->aerr,101,"backspace")
|
|
b= &f__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 (f__nowreading(b))
|
|
err(a->aerr,errno,"backspace")
|
|
}
|
|
if(b->url>0)
|
|
{
|
|
x=ftell(b->ufd);
|
|
y = x % b->url;
|
|
if(y == 0) x--;
|
|
x /= b->url;
|
|
x *= b->url;
|
|
(void) fseek(b->ufd,x,SEEK_SET);
|
|
return(0);
|
|
}
|
|
|
|
if(b->ufmt==0)
|
|
{ (void) fseek(b->ufd,-(long)sizeof(int),SEEK_CUR);
|
|
(void) fread((char *)&n,sizeof(int),1,b->ufd);
|
|
(void) fseek(b->ufd,-(long)n-2*sizeof(int),SEEK_CUR);
|
|
return(0);
|
|
}
|
|
#ifdef MSDOS
|
|
w = -1;
|
|
#endif
|
|
for(ndec = 1;; ndec = 0)
|
|
{
|
|
y = x = ftell(b->ufd);
|
|
if(x < sizeof(buf))
|
|
x = 0;
|
|
else
|
|
x -= sizeof(buf);
|
|
(void) fseek(b->ufd,x,SEEK_SET);
|
|
n=fread(buf,1,(int)(y-x), b->ufd);
|
|
for(i = n - ndec; --i >= 0; )
|
|
{
|
|
if(buf[i]!='\n') continue;
|
|
#ifdef MSDOS
|
|
for(j = k = 0; j <= i; j++)
|
|
if (buf[j] == '\n')
|
|
k++;
|
|
fseek(b->ufd,x,SEEK_SET);
|
|
for(;;)
|
|
if (getc(b->ufd) == '\n') {
|
|
if ((z = ftell(b->ufd)) >= y && ndec) {
|
|
if (w == -1)
|
|
goto break2;
|
|
break;
|
|
}
|
|
if (--k <= 0)
|
|
return 0;
|
|
w = z;
|
|
}
|
|
fseek(b->ufd, w, SEEK_SET);
|
|
#else
|
|
fseek(b->ufd,(long)(i+1-n),SEEK_CUR);
|
|
#endif
|
|
return(0);
|
|
}
|
|
#ifdef MSDOS
|
|
break2:
|
|
#endif
|
|
if(x==0)
|
|
{
|
|
(void) fseek(b->ufd, 0L, SEEK_SET);
|
|
return(0);
|
|
}
|
|
else if(n<=0) err(a->aerr,(EOF),"backspace")
|
|
(void) fseek(b->ufd, x, SEEK_SET);
|
|
}
|
|
}
|