optimize split_matrix function

[ivanz851]

I optimized split_matrix function by removing duplicate code to the extract_submatrix function, and added tests to test_strassen_matrix_multiplication.py file

[josmithua]

This increases readability and maintainability of the code, but certainly does not "optimize" the algorithm, for you have added the extra overhead of calling a function, which will actually slow down the algorithm.

[ivanz851]

This increases readability and maintainability of the code, but certainly does not "optimize" the algorithm, for you have added the extra overhead of calling a function, which will actually slow down the algorithm.

Actually, my code with extract_submatrix function is not less efficient than the original one, since there is exactly same number of conditional jumps. This can be checked using godbolt.org: comparison. If you follow the link, you can see disassembly of my revision of the code on the left and of the original code on the right. In original code, there are 8 FOR_ITER jumps and 8 JUMP_BACKWARD jumps. In new code, there are 2 FOR_ITER jumps and 2 JUMP_BACKWARD jumps in extract_submatrix function, which is called 4 times, so in sum we have same 8 FOR_ITER jumps and 8 JUMP_BACKWARD jumps. That's why I think code with extract_submatrix function is not slower and can be used for better readability.

[ivanz851]

@josmithua

[josmithua]

@ivanz851 Thanks, I learned something new today. Cheers