[src/trunk]: src Document __builtin_constant_p().

[jruoho <jruoho%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/7adcaefd930f
branches:  trunk
changeset: 759886:7adcaefd930f
user:      jruoho <jruoho%NetBSD.org@localhost>
date:      Sun Dec 19 10:07:23 2010 +0000

description:
Document __builtin_constant_p().

diffstat:

 distrib/sets/lists/comp/mi            |   5 +-
 share/man/man3/Makefile               |   4 +-
 share/man/man3/__builtin_constant_p.3 |  78 +++++++++++++++++++++++++++++++++++
 3 files changed, 84 insertions(+), 3 deletions(-)

diffs (130 lines):

diff -r 6cbb8abbe420 -r 7adcaefd930f distrib/sets/lists/comp/mi
--- a/distrib/sets/lists/comp/mi        Sun Dec 19 09:33:52 2010 +0000
+++ b/distrib/sets/lists/comp/mi        Sun Dec 19 10:07:23 2010 +0000
@@ -1,4 +1,4 @@
-#      $NetBSD: mi,v 1.1556 2010/12/19 09:30:49 jruoho Exp $
+#      $NetBSD: mi,v 1.1557 2010/12/19 10:07:23 jruoho Exp $
 #
 # Note: don't delete entries from here - mark them as "obsolete" instead.
 #
@@ -4908,6 +4908,7 @@
 ./usr/share/man/cat3/__aligned.0               comp-c-catman           .cat
 ./usr/share/man/cat3/__alignof__.0             comp-c-catman           .cat
 ./usr/share/man/cat3/__arraycount.0            comp-c-catman           .cat
+./usr/share/man/cat3/__builtin_constant_p.0    comp-c-catman           .cat
 ./usr/share/man/cat3/__builtin_frame_address.0 comp-c-catman           .cat
 ./usr/share/man/cat3/__builtin_object_size.0   comp-c-catman           .cat
 ./usr/share/man/cat3/__builtin_return_address.0        comp-c-catman           .cat
@@ -10999,6 +11000,7 @@
 ./usr/share/man/html3/__aligned.html           comp-c-htmlman          html
 ./usr/share/man/html3/__alignof__.html         comp-c-htmlman          html
 ./usr/share/man/html3/__arraycount.html                comp-c-htmlman          html
+./usr/share/man/html3/__builtin_constant_p.html                comp-c-htmlman          html
 ./usr/share/man/html3/__builtin_frame_address.html     comp-c-htmlman          html
 ./usr/share/man/html3/__builtin_object_size.html       comp-c-htmlman          html
 ./usr/share/man/html3/__builtin_return_address.html    comp-c-htmlman          html
@@ -16890,6 +16892,7 @@
 ./usr/share/man/man3/__aligned.3               comp-c-man              .man
 ./usr/share/man/man3/__alignof__.3             comp-c-man              .man
 ./usr/share/man/man3/__arraycount.3            comp-c-man              .man
+./usr/share/man/man3/__builtin_constant_p.3    comp-c-man              .man
 ./usr/share/man/man3/__builtin_frame_address.3 comp-c-man              .man
 ./usr/share/man/man3/__builtin_object_size.3   comp-c-man              .man
 ./usr/share/man/man3/__builtin_return_address.3        comp-c-man              .man
diff -r 6cbb8abbe420 -r 7adcaefd930f share/man/man3/Makefile
--- a/share/man/man3/Makefile   Sun Dec 19 09:33:52 2010 +0000
+++ b/share/man/man3/Makefile   Sun Dec 19 10:07:23 2010 +0000
@@ -1,9 +1,9 @@
-#      $NetBSD: Makefile,v 1.66 2010/12/19 09:30:50 jruoho Exp $
+#      $NetBSD: Makefile,v 1.67 2010/12/19 10:07:24 jruoho Exp $
 #      @(#)Makefile    8.2 (Berkeley) 12/13/93
 
 MAN=   _DIAGASSERT.3 __CONCAT.3 __UNCONST.3 CMSG_DATA.3 \
        __alignof__.3 __arraycount.3 \
-       __builtin_return_address.3 __insn_barrier.3 \
+       __builtin_constant_p.3 __builtin_return_address.3 __insn_barrier.3 \
        assert.3 attribute.3 bits.3 bitstring.3 \
        cdefs.3 dirent.3 dlfcn.3 dl_iterate_phdr.3 end.3 \
        fast_divide32.3 ffs32.3 gcq.3 \
diff -r 6cbb8abbe420 -r 7adcaefd930f share/man/man3/__builtin_constant_p.3
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/share/man/man3/__builtin_constant_p.3     Sun Dec 19 10:07:23 2010 +0000
@@ -0,0 +1,78 @@
+.\" $NetBSD: __builtin_constant_p.3,v 1.1 2010/12/19 10:07:24 jruoho Exp $
+.\"
+.\" Copyright (c) 2010 Jukka Ruohonen <jruohonen%iki.fi@localhost>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+.\" POSSIBILITY OF SUCH DAMAGE.
+.\"
+.Dd December 19, 2010
+.Dt __BUILTIN_CONSTANT_P 3
+.Os
+.Sh NAME
+.Nm __builtin_constant_p
+.Nd GNU extension to determine compile time constants
+.Sh SYNOPSIS
+.Ft int
+.Fn __builtin_constant_p "value"
+.Sh DESCRIPTION
+The
+.Fn __builtin_constant_p
+is a
+.Tn GNU
+extension for determining whether a value
+is known to be constant at compile time.
+The function is closely related to the concept of
+.Dq constant folding
+used by modern optimizing compilers.
+.Pp
+If the
+.Fa value
+is known to be a compile-time constant, a value 1 is returned.
+If
+.Fn __builtin_constant_p
+returns 0, the
+.Fa value
+is not a compile-time constant in the sense that
+.Xr gcc 1
+was unable to determine whether the value is constant or not.
+.Sh EXAMPLES
+A typical example of the use of
+.Fn __builtin_constant_p
+involves a situation where it may be desirable to
+fold the computation if it involves a constant,
+but a function call is needed otherwise.
+For instance,
+.Xr bswap 16
+is defined in
+.Nx
+as:
+.Bd -literal -offset indent
+#define bswap16(x) \\
+        (__builtin_constant_p((x)) ? \\
+         __byte_swap_u16_constant(x) : __BYTE_SWAP_U16_VARIABLE(x))
+.Ed
+.Sh SEE ALSO
+.Xr gcc 1 ,
+.Xr __builtin_object_size 3 ,
+.Xr __builtin_return_address 3
+.Sh CAVEATS
+This is a non-standard, compiler-specific extension.