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/* read for MMIXware.

   Copyright (C) 2001 Hans-Peter Nilsson

   Permission to use, copy, modify, and distribute this software is

   freely granted, provided that the above copyright notice, this notice

   and the following disclaimer are preserved with no changes.

   THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR

   IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED

   WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

   PURPOSE.  */

#include <_ansi.h>

#include <sys/types.h>

#include <sys/stat.h>

#include "sys/syscall.h"

#include <errno.h>

int

_read (int file,

       char *ptr,

       size_t len)

{

  long ret;

  if ((unsigned int) file >= 32 || _MMIX_allocated_filehandle[file] == 0)

    {

      errno = EBADF;

      return -1;

    }

  if (isatty(file))

    {

      ret = TRAP3f (SYS_Fgets, file, ptr, len);

      if (ret == -1)

        return 0;

      return ret;

    }

  ret = TRAP3f (SYS_Fread, file, ptr, len);

  /* Map the return codes:

     -1-len: an error.  We return -1.

     0: success.  We return len.

     n-len: end-of-file after n chars read.  We return n. */

  if (ret == 0)

    return len;

  if (ret == -1 - (long) len)

    {

      /* We don't know the nature of the failure, so this is an

         approximation.  */

      errno = EIO;

      return -1;

    }

  return ret + len;

}