/* read for MMIXware.

   Copyright (C) 2001 Hans-Peter Nilsson.

   Permission to use, copy, modify, and distribute this software is freely
   granted, provided that this notice is 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;
    }

  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;
}