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Editing: select.h

/* Copyright (C) 1997-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#ifndef _SYS_SELECT_H
# error "Never use <bits/select.h> directly; include <sys/select.h> instead."
#endif

#include <bits/wordsize.h>

#if defined __GNUC__ && __GNUC__ >= 2

# if __WORDSIZE == 64
#  define __FD_ZERO_STOS "stosq"
# else
#  define __FD_ZERO_STOS "stosl"
# endif

# define __FD_ZERO(fdsp) \
  do {									      \
    int __d0, __d1;							      \
    __asm__ __volatile__ ("cld; rep; " __FD_ZERO_STOS			      \
			  : "=c" (__d0), "=D" (__d1)			      \
			  : "a" (0), "0" (sizeof (fd_set)		      \
					  / sizeof (__fd_mask)),	      \
			    "1" (&__FDS_BITS (fdsp)[0])			      \
			  : "memory");					      \
  } while (0)

#else	/* ! GNU CC */

/* We don't use `memset' because this would require a prototype and
   the array isn't too big.  */
# define __FD_ZERO(set)  \
  do {									      \
    unsigned int __i;							      \
    fd_set *__arr = (set);						      \
    for (__i = 0; __i < sizeof (fd_set) / sizeof (__fd_mask); ++__i)	      \
      __FDS_BITS (__arr)[__i] = 0;					      \
  } while (0)

#endif	/* GNU CC */

#define __FD_SET(d, set) \
  ((void) (__FDS_BITS (set)[__FD_ELT (d)] |= __FD_MASK (d)))
#define __FD_CLR(d, set) \
  ((void) (__FDS_BITS (set)[__FD_ELT (d)] &= ~__FD_MASK (d)))
#define __FD_ISSET(d, set) \
  ((__FDS_BITS (set)[__FD_ELT (d)] & __FD_MASK (d)) != 0)

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