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#include "config.h"
#include <sys/types.h>
#include "f2c.h"
#include "fio.h"
integer
f_back (alist * a)
{
unit *b;
off_t 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;
FSEEK (f, x, SEEK_SET);
return (0);
}
if (b->ufmt == 0)
{
FSEEK (f, -(off_t) sizeof (uiolen), SEEK_CUR);
fread ((char *) &n, sizeof (uiolen), 1, f);
FSEEK (f, -(off_t) 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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