https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=5717262b8ecfed0f7fab63e2c09c78991e36f9dd

commit 5717262b8ecfed0f7fab63e2c09c78991e36f9dd
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Mon Aug 3 12:40:43 2020 +0200

    select.h: update FD macros to latest FreeBSD, fix type conversion warning
    
    Compiling
    
    #include <sys/select.h>
    void f(int X)
    {
      fd_set set;
      FD_ZERO(&set);
      FD_SET(X,&set);
      FD_CLR(X+1,&set);
      (void)FD_ISSET(X+2,&set);
    }
    
    results in plenty of gcc warnings when compiled with
    -Wconversion -Wsign-conversion:
    
      fds.c:7:2: warning: conversion to ‘long unsigned int’ from ‘int’ may
        FD_SET(X,&set);
        ^~~~~~
      [...]
    
    The unsigned NFDBITS macro combined with the signed 1L constant
    are causing lots of implicit signed/unsigned type conversions.
    
    Fix this by updating the FD_* macro code to the latest from FreeBSD
    and adding an (int) cast to _NFDBITS.
    
    As a side-effect, this fixes the visibility of NFDBITS and
    fds_bits (only if __BSD_VISIBLE).
    
    This also eliminates the old, outdated fd_set workaround.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 newlib/libc/include/sys/select.h | 68 ++++++++++++++++++++++++----------------
 1 file changed, 41 insertions(+), 27 deletions(-)

diff --git a/newlib/libc/include/sys/select.h b/newlib/libc/include/sys/select.h
index 1e5d895bb..a5cd6c3fe 100644
--- a/newlib/libc/include/sys/select.h
+++ b/newlib/libc/include/sys/select.h
@@ -27,33 +27,47 @@ typedef	__sigset_t	sigset_t;
  * FD_SETSIZE may be defined by the user, but the default here
  * should be >= NOFILE (param.h).
  */
-#  ifndef	FD_SETSIZE
-#	define	FD_SETSIZE	64
-#  endif
-
-typedef	unsigned long	fd_mask;
-#  define	NFDBITS	(sizeof (fd_mask) * 8)	/* bits per mask */
-#  ifndef	_howmany
-#	define	_howmany(x,y)	(((x)+((y)-1))/(y))
-#  endif
-
-/* We use a macro for fd_set so that including Sockets.h afterwards
-   can work.  */
-typedef	struct _types_fd_set {
-	fd_mask	fds_bits[_howmany(FD_SETSIZE, NFDBITS)];
-} _types_fd_set;
-
-#define fd_set _types_fd_set
-
-#  define	FD_SET(n, p)	((p)->fds_bits[(n)/NFDBITS] |= (1L << ((n) % NFDBITS)))
-#  define	FD_CLR(n, p)	((p)->fds_bits[(n)/NFDBITS] &= ~(1L << ((n) % NFDBITS)))
-#  define	FD_ISSET(n, p)	((p)->fds_bits[(n)/NFDBITS] & (1L << ((n) % NFDBITS)))
-#  define	FD_ZERO(p)	(__extension__ (void)({ \
-     size_t __i; \
-     char *__tmp = (char *)p; \
-     for (__i = 0; __i < sizeof (*(p)); ++__i) \
-       *__tmp++ = 0; \
-}))
+#ifndef	FD_SETSIZE
+#define	FD_SETSIZE	64
+#endif
+
+typedef unsigned long	__fd_mask;
+#if __BSD_VISIBLE
+typedef __fd_mask	fd_mask;
+#endif
+
+#define _NFDBITS	((int)sizeof(__fd_mask) * 8) /* bits per mask */
+#if __BSD_VISIBLE
+#define NFDBITS		_NFDBITS
+#endif
+
+#ifndef	_howmany
+#define	_howmany(x,y)	(((x) + ((y) - 1)) / (y))
+#endif
+
+typedef	struct fd_set {
+	__fd_mask	__fds_bits[_howmany(FD_SETSIZE, _NFDBITS)];
+} fd_set;
+#if __BSD_VISIBLE
+#define fds_bits	__fds_bits
+#endif
+
+#define __fdset_mask(n)	((__fd_mask)1 << ((n) % _NFDBITS))
+#define FD_CLR(n, p)	((p)->__fds_bits[(n)/_NFDBITS] &= ~__fdset_mask(n))
+#if __BSD_VISIBLE
+#define FD_COPY(f, t)	(void)(*(t) = *(f))
+#endif
+#define FD_ISSET(n, p)	(((p)->__fds_bits[(n)/_NFDBITS] & __fdset_mask(n)) != 0)
+#define FD_SET(n, p)	((p)->__fds_bits[(n)/_NFDBITS] |= __fdset_mask(n))
+#define FD_ZERO(p) do {					\
+        fd_set *_p;					\
+        __size_t _n;					\
+							\
+        _p = (p);					\
+        _n = _howmany(FD_SETSIZE, _NFDBITS);		\
+        while (_n > 0)					\
+                _p->__fds_bits[--_n] = 0;		\
+} while (0)
 
 #if !defined (__INSIDE_CYGWIN_NET__)