gallium/util: rewrite global constructor system for half floats (GCC/MSVC only!)

NOTE: this commit will cause Gallium to fail to build on any compiler
      except GCC, the Microsoft C compiler and compatible compilers that
      claim to be one of those.

This commit removes the u_gctors.cpp mechanism, in favor of using
compiler-specific syntax to add global constructors from C files.

This solves the problem of u_gctors.o not being pulled from static
libraries and avoids using C++.

However, it needs compiler-specific support for every compiler.

The Microsoft C compiler support has not been tested.

progs/gallium/unit/u_format_test.c

@@ -404,7 +404,6 @@ int main(int argc, char **argv)
 {
    boolean success;
 
-   util_half_init_tables();
    util_format_s3tc_init();
 
    success = test_all();

src/gallium/auxiliary/Makefile

@@ -139,9 +139,6 @@ C_SOURCES = \
 	#vl/vl_csc.c \
 	#vl/vl_shader_build.c \
 
-CPP_SOURCES = \
-	util/u_gctors.cpp
-
 GALLIVM_SOURCES = \
         gallivm/lp_bld_alpha.c \
         gallivm/lp_bld_arit.c \

src/gallium/auxiliary/util/u_gctors.cpp

@@ -1,17 +0,0 @@
-/* this file uses the C++ global constructor mechanism to automatically
-   initialize global data
-
-   __attribute__((constructor)) allows to do this in C, but is GCC-only
-*/
-
-#include "u_half.h"
-
-struct util_gctor_t
-{
-	util_gctor_t()
-	{
-		util_half_init_tables();
-	}
-};
-
-static struct util_gctor_t util_gctor;

src/gallium/auxiliary/util/u_half.c

@@ -50,6 +50,7 @@
  */
 
 #include "util/u_half.h"
+#include "util/u_init.h"
 
 uint32_t util_half_to_float_mantissa_table[2048];
 uint32_t util_half_to_float_exponent_table[64];
@@ -57,7 +58,7 @@ uint32_t util_half_to_float_offset_table[64];
 uint16_t util_float_to_half_base_table[512];
 uint8_t util_float_to_half_shift_table[512];
 
-void util_half_init_tables(void)
+static void util_half_init_tables(void)
 {
 	int i;
 
@@ -153,3 +154,5 @@ void util_half_init_tables(void)
 		util_float_to_half_shift_table[256 + i] = util_float_to_half_shift_table[i];
 	}
 }
+
+UTIL_INIT(util_half_init_tables);

src/gallium/auxiliary/util/u_half.h

@@ -4,7 +4,6 @@
 #include "pipe/p_compiler.h"
 #include "u_math.h"
 
-
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -59,10 +58,6 @@ util_float_to_half(float f)
 	return util_floatui_to_half(i.ui);
 }
 
-/* called by u_gctors.cpp, which defines the prototype itself */
-void util_half_init_tables(void);
-
-
 #ifdef __cplusplus
 }
 #endif

src/gallium/auxiliary/util/u_init.h

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2010 Luca Barbieri
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE COPYRIGHT OWNER(S) AND/OR ITS SUPPLIERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ **************************************************************************/
+
+#ifndef U_INIT_H
+#define U_INIT_H
+
+/* Use UTIL_INIT(f) to have f called at program initialization.
+   Note that it is only guaranteed to be called if any symbol in the
+   .c file it is in sis referenced by the program.
+
+   UTIL_INIT functions are called in arbitrary order.
+*/
+
+#ifdef __cplusplus
+/* use a C++ global constructor */
+#define UTIL_INIT(f) struct f##__gctor_t {f##__gctor_t() {x();}} f##__gctor;
+#elif defined(_MSC_VER)
+/* add a pointer to the section where MSVC stores global constructor pointers */
+/* see http://blogs.msdn.com/vcblog/archive/2006/10/20/crt-initialization.aspx and
+   http://stackoverflow.com/questions/1113409/attribute-constructor-equivalent-in-vc */
+#define UTIL_INIT(f) static void __cdecl f##__init(void) {f();}; __declspec(allocate(".CRT$XCU")) void (__cdecl* f##__xcu)(void) = f##__init;
+#elif defined(__GNUC__)
+#define UTIL_INIT(f) static void f##__init(void) __attribute__((constructor)); static void f##__init(void) {f();}
+#else
+#error Unsupported compiler: please find out how to implement global initializers in C on it
+#endif
+
+#endif
+