gold patch committed: Make swapping less glibc dependent

[Ian Lance Taylor <iant at google dot com>]

The current code in gold to do byte swapping uses macros which are only
available from glibc.  I committed this patch to make it more flexible.
It will now use the gcc builtin functions if they are available (gcc 4.3
or later), otherwise the glibc <byteswap.h> functions, otherwise inline
functions written in ordinary C++.  Hopefully this will be more
portable.

Ian


gold:/
2009-03-01  Ian Lance Taylor  <iant@google.com>

	* configure.ac: Check for byteswap.h.
	* configure: Rebuild.
	* config.in: Rebuild.

elfcpp:/
2009-03-01  Ian Lance Taylor  <iant@google.com>

	* elfcpp_swap.h: #include "config.h".  Only #include <byteswap.h>
	if HAVE_BYTESWAP_H is defined; if not, provide definitions for
	bswap_{16,32,64}.  For gcc 4.3 and later, use the builtin bswap
	functions.  Check WORDS_BIGENDIAN rather than __BYTE_ORDER.


Index: gold/configure.ac
===================================================================
RCS file: /cvs/src/src/gold/configure.ac,v
retrieving revision 1.36
diff -p -u -r1.36 configure.ac
--- gold/configure.ac	12 Dec 2008 16:23:27 -0000	1.36
+++ gold/configure.ac	2 Mar 2009 02:43:08 -0000
@@ -317,6 +317,7 @@ AC_LANG_PUSH(C++)
 
 AC_CHECK_HEADERS(tr1/unordered_set tr1/unordered_map)
 AC_CHECK_HEADERS(ext/hash_map ext/hash_set)
+AC_CHECK_HEADERS(byteswap.h)
 AC_CHECK_FUNCS(mallinfo)
 
 # gcc 4.3.0 doesn't recognize the printf attribute on a template
Index: elfcpp/elfcpp_swap.h
===================================================================
RCS file: /cvs/src/src/elfcpp/elfcpp_swap.h,v
retrieving revision 1.5
diff -p -u -r1.5 elfcpp_swap.h
--- elfcpp/elfcpp_swap.h	3 Apr 2008 23:33:20 -0000	1.5
+++ elfcpp/elfcpp_swap.h	2 Mar 2009 02:43:09 -0000
@@ -1,6 +1,6 @@
 // elfcpp_swap.h -- Handle swapping for elfcpp   -*- C++ -*-
 
-// Copyright 2006, 2007, Free Software Foundation, Inc.
+// Copyright 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
 // Written by Ian Lance Taylor <iant@google.com>.
 
 // This file is part of elfcpp.
@@ -37,8 +37,54 @@
 #define ELFCPP_SWAP_H
 
 #include <stdint.h>
-#include <endian.h>
+
+// We need an autoconf-generated config.h file for endianness and
+// swapping.  We check two macros: WORDS_BIGENDIAN and
+// HAVE_BYTESWAP_H.
+
+#include "config.h"
+
+#ifdef HAVE_BYTESWAP_H
 #include <byteswap.h>
+#else
+// Provide our own versions of the byteswap functions.
+inline uint16_t
+bswap_16(uint16_t v)
+{
+  return ((v >> 8) & 0xff) | ((v & 0xff) << 8);
+}
+
+inline uint32_t
+bswap_32(uint32_t v)
+{
+  return (  ((v & 0xff000000) >> 24)
+	  | ((v & 0x00ff0000) >>  8)
+	  | ((v & 0x0000ff00) <<  8)
+	  | ((v & 0x000000ff) << 24));
+}
+
+inline uint64_t
+bswap_64(uint64_t v)
+{
+  return (  ((v & 0xff00000000000000ULL) >> 56)
+	  | ((v & 0x00ff000000000000ULL) >> 40)
+	  | ((v & 0x0000ff0000000000ULL) >> 24)
+	  | ((v & 0x000000ff00000000ULL) >>  8)
+	  | ((v & 0x00000000ff000000ULL) <<  8)
+	  | ((v & 0x0000000000ff0000ULL) << 24)
+	  | ((v & 0x000000000000ff00ULL) << 40)
+	  | ((v & 0x00000000000000ffULL) << 56));
+}
+#endif // !defined(HAVE_BYTESWAP_H)
+
+// gcc 4.3 and later provides __builtin_bswap32 and __builtin_bswap64.
+
+#if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))
+#undef bswap_32
+#define bswap_32 __builtin_bswap32
+#undef bswap_64
+#define bswap_64 __builtin_bswap64
+#endif
 
 namespace elfcpp
 {
@@ -49,7 +95,13 @@ struct Endian
 {
  public:
   // Used for template specializations.
-  static const bool host_big_endian = __BYTE_ORDER == __BIG_ENDIAN;
+  static const bool host_big_endian = 
+#ifdef WORDS_BIGENDIAN
+    true
+#else
+    false
+#endif
+    ;
 };
 
 // Valtype_base is a template based on size (8, 16, 32, 64) which