Fix C++20 -Wdeprecated-enum-enum-conversion warning by using integer types for matrix::num_rows and num_cols

[NBickford-NV]

Hi! This fixes a -Wdeprecated-enum-enum-conversion warning on GCC and Clang we ran into when compiling basisu's files inside a C++20 project. Basisu's CMakeLists.txt specifies C++17, but this can be reproduced without a custom CMake script by running

g++ -O3 -DNDEBUG -std=c++20 -o temp.o -c basis_universal/encoder/basisu_astc_hdr_6x6_enc.cpp

This produces the following warning:

in file included from basis_universal/encoder/basisu_enc.h:4310,
                 from basis_universal/encoder/basisu_astc_hdr_6x6_enc.h:3,
                 from basis_universal/encoder/basisu_astc_hdr_6x6_enc.cpp:2:
basis_universal/encoder/basisu_math.h: In instantiation of ‘bu_math::matrix<(X::num_rows * Y::num_rows), (X::num_cols * Y::num_cols), typename X::scalar_type> bu_math::matrix_kronecker_product(const X&, const Y&) [with X = matrix<2, 2, float>; Y = matrix<1, 2, float>; typename X::scalar_type = float]’:
basis_universal/encoder/basisu_math.h:2411:57:   required from here
basis_universal/encoder/basisu_math.h:2362:60: warning: arithmetic between different enumeration types ‘bu_math::matrix<2, 2, float>::<unnamed enum>’ and ‘bu_math::matrix<1, 2, float>::<unnamed enum>’ is deprecated [-Wdeprecated-enum-enum-conversion]
 2362 |         template<typename X, typename Y> matrix<X::num_rows* Y::num_rows, X::num_cols* Y::num_cols, typename X::scalar_type> matrix_kronecker_product(const X& a, const Y& b)
      |                                                    ~~~~~~~~^~~~~~~~~~~~~

Previously, num_rows and num_cols were members of an anonymous union within each templated matrix type:

	template <uint32_t R, uint32_t C, typename T>
	class matrix
	{
	public:
		typedef T scalar_type;
		enum
		{
			num_rows = R,
			num_cols = C
		};
                ...

This meant that arithmetic operations between num_rows and num_cols of different matrix types were technically implicitly converting between different types, resulting in the warning above. Changing the types of num_rows and num_cols to static const uint32_t fixes this.

Thank you!

[richgel999]

Thank you! Will merge.

[richgel999]

This has been merged into basisu v2.0 coming in Jan. 2026.

[NBickford-NV]

Thank you Rich!