CMake: checking type sizes (#48)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 802f71a..d723616 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -58,11 +58,9 @@
 check_include_files(stdint.h INCLUDE_STDINT_H)
 check_include_files(sys/types.h INCLUDE_SYS_TYPES_H)
 
-set(SIZE16 int16_t)
-set(USIZE16 uint16_t)
-set(SIZE32 int32_t)
-set(USIZE32 uint32_t)
-set(SIZE64 int64_t)
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
+
+include(CheckSizes)
 
 configure_file(include/ogg/config_types.h.in ${CMAKE_CURRENT_BINARY_DIR}/include/ogg/config_types.h @ONLY)
 
diff --git a/cmake/CheckSizes.cmake b/cmake/CheckSizes.cmake
new file mode 100644
index 0000000..4d6c8a0
--- /dev/null
+++ b/cmake/CheckSizes.cmake
@@ -0,0 +1,73 @@
+include(CheckTypeSize)
+
+check_type_size("int16_t" INT16_SIZE LANGUAGE C)
+check_type_size("uint16_t" UINT16_SIZE LANGUAGE C)
+check_type_size("u_int16_t" U_INT16_SIZE LANGUAGE C)
+check_type_size("int32_t" INT32_SIZE LANGUAGE C)
+check_type_size("uint32_t" UINT32_SIZE LANGUAGE C)
+check_type_size("u_int32_t" U_INT32_SIZE LANGUAGE C)
+check_type_size("int64_t" INT64_SIZE LANGUAGE C)
+check_type_size("short" SHORT_SIZE LANGUAGE C)
+check_type_size("int" INT_SIZE LANGUAGE C)
+check_type_size("long" LONG_SIZE LANGUAGE C)
+check_type_size("long long" LONG_LONG_SIZE LANGUAGE C)
+
+if(INT16_SIZE EQUAL 2)
+    set(SIZE16 "int16_t")
+elseif(SHORT_SIZE EQUAL 2)
+    set(SIZE16 "short")
+elseif(INT_SIZE EQUAL 2)
+    set(SIZE16 "int")
+else()
+    message(FATAL_ERROR "No 16 bit type found on this platform!")
+endif()
+
+if(UINT16_SIZE EQUAL 2)
+    set(USIZE16 "uint16_t")
+elseif(SHORT_SIZE EQUAL 2)
+    set(USIZE16 "unsigned short")
+elseif(INT_SIZE EQUAL 2)
+    set(USIZE16 "unsigned int")
+elseif(U_INT_SIZE EQUAL 2)
+    set(USIZE16 "u_int16_t")
+else()
+    message(FATAL_ERROR "No unsigned 16 bit type found on this platform!")
+endif()
+
+if(INT32_SIZE EQUAL 4)
+    set(SIZE32 "int32_t")
+elseif(SHORT_SIZE EQUAL 4)
+    set(SIZE32 "short")
+elseif(INT_SIZE EQUAL 4)
+    set(SIZE32 "int")
+elseif(LONG_SIZE EQUAL 4)
+    set(SIZE16 "long")
+else()
+    message(FATAL_ERROR "No 32 bit type found on this platform!")
+endif()
+
+if(UINT32_SIZE EQUAL 4)
+    set(USIZE32 "uint32_t")
+elseif(SHORT_SIZE EQUAL 4)
+    set(USIZE32 "unsigned short")
+elseif(INT_SIZE EQUAL 4)
+    set(USIZE32 "unsigned int")
+elseif(LONG_SIZE EQUAL 4)
+    set(USIZE32 "unsigned long")
+elseif(U_INT_SIZE EQUAL 4)
+    set(USIZE32 "u_int32_t")
+else()
+    message(FATAL_ERROR "No unsigned 32 bit type found on this platform!")
+endif()
+
+if(INT64_SIZE EQUAL 8)
+    set(SIZE64 "int64_t")
+elseif(INT_SIZE EQUAL 8)
+    set(SIZE64 "int")
+elseif(LONG_SIZE EQUAL 8)
+    set(SIZE64 "long")
+elseif(LONG_LONG_SIZE EQUAL 8)
+    set(SIZE64 "long long")
+else()
+    message(FATAL_ERROR "No 64 bit type found on this platform!")
+endif()