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Atari Mega Archive 1
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gnulib
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libsrc98.zoo
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isatty.c
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1993-03-01
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/* from the original GCC TOS library by jrd */
/* this algorithm is due to Allan Pratt @ Atari. Thanks Allan! */
#include <errno.h>
#include <osbind.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <device.h>
#include "lib.h"
int isatty(fd)
int fd;
{
int rc;
long oldloc, seekval;
int handle = __OPEN_INDEX(fd);
struct _device *dev;
if ((short)handle < 0)
return(1);
dev = _dev_fd(fd);
if (dev && ((dev->open) || (dev->dev == 0xfffd)))
{ /* a special device or PRN: */
return 0;
}
if (handle < __NHANDLES)
if (__open_stat[handle].status != FH_UNKNOWN)
return(__open_stat[handle].status == FH_ISATTY);
oldloc = Fseek (0L, fd, SEEK_CUR); /* seek zero bytes from current loc */
if ((seekval = Fseek (1L, fd, SEEK_SET)) != 0) /* try to seek ahead one byte */
if ((seekval > 0) || (seekval == ((long)(-EBADARG)))) /* out of range... */
rc = 0; /* file, not a tty */
else
{
errno = EBADF; /* any other error returns "invalid handle" */
/* because you can't tell */
rc = 0;
}
else
rc = 1; /* yes, tty (Fseek returns 0 only for ttys) */
(void)Fseek(oldloc, fd, SEEK_SET); /* seek back to original location */
if (handle < __NHANDLES)
if (rc)
__open_stat[handle].status = FH_ISATTY;
else
__open_stat[handle].status = FH_ISAFILE;
return (rc); /* return true, false, or error */
}