check endianness of floats

cmake/CheckEndianness.cmake

@@ -0,0 +1,18 @@
+include(TestBigEndian)
+
+macro(define_python_endianness_macros)
+  TEST_BIG_ENDIAN(WORDS_BIGENDIAN)
+
+  # Test for float endianness
+  try_run(RESULT_VAR COMPILE_VAR
+    ${CMAKE_BINARY_DIR}/check_float_endianness_result
+    ${CMAKE_SOURCE_DIR}/cmake/check_float_endianness.c
+  )
+  if(RESULT_VAR EQUAL 1)
+    message(STATUS "System uses big-endian floating point format")
+    set(FLOAT_WORDS_BIGENDIAN 1)
+  else()
+    message(STATUS "System uses little-endian floating point format")
+    set(FLOAT_WORDS_BIGENDIAN 0)
+  endif()
+endmacro()

cmake/ConfigureChecks.cmake

@@ -9,7 +9,7 @@ include(CheckLibraryExists)
 include(CheckSymbolExists)
 include(CheckVariableExists)
 include(cmake/PlatformTest.cmake)
-include(TestBigEndian)
+include(cmake/CheckEndianness.cmake)
 
 message(STATUS "The system name is ${CMAKE_SYSTEM_NAME}")
 message(STATUS "The system processor is ${CMAKE_SYSTEM_PROCESSOR}")
@@ -713,7 +713,7 @@ add_cond(CMAKE_REQUIRED_LIBRARIES HAVE_LIBINTL ${HAVE_LIBINTL})
 add_cond(CMAKE_REQUIRED_LIBRARIES HAVE_LIBUTIL "${LIBUTIL_LIBRARIES}")
 add_cond(CMAKE_EXTRA_INCLUDE_FILES HAVE_WCHAR_H wchar.h)
 
-TEST_BIG_ENDIAN(WORDS_BIGENDIAN)
+define_python_endianness_macros()
 
 check_type_size(double SIZEOF_DOUBLE) # libffi and cpython
 check_type_size(float SIZEOF_FLOAT)

cmake/check_float_endianness.c

@@ -0,0 +1,18 @@
+#include <stdio.h>
+
+int main() {
+    // Test with a known float value (1.0f)
+    float test = 1.0f;
+    unsigned char *bytes = (unsigned char*)&test;
+
+    // The float 1.0f has a known IEEE-754 representation
+    // In big-endian, the first byte would be 0x3F
+    // In little-endian, the first byte would be 0x00
+    if (bytes[0] == 0x3F) {
+        // Big-endian float
+        return 1;
+    } else {
+        // Little-endian float
+        return 0;
+    }
+}