generic math

meta_math.h

#ifndef DETAIL_META_HEADER_MATH
#define DETAIL_META_HEADER_MATH

#include <stddef.h>

#define meta_int_cmp(X, ...) \
	meta_int_cmp(sizeof(X), sizeof(__VA_ARGS__), (typeof(X))-1 < 0, (typeof(__VA_ARGS__))-1 < 0, (unsigned char*)&(typeof(X)){ (X) }, (unsigned char*)&(typeof(__VA_ARGS__)){ (__VA_ARGS__) })
[[maybe_unused]] static inline int (meta_int_cmp)(size_t a_size, size_t b_size, bool a_signed, bool b_signed, unsigned char* a_data, unsigned char* b_data) {
	static constexpr int sign_mask = ~((unsigned char)-1 >> 1);
	bool a_sign = a_signed && (a_data[a_size - 1] & sign_mask);
	bool b_sign = b_signed && (b_data[b_size - 1] & sign_mask);
	if (a_sign != b_sign) {
		return b_sign - a_sign;
	}
	for (size_t i = (a_size < b_size) ? b_size : a_size; i--;) {
		unsigned char a = (i < a_size) ? a_data[i] : (unsigned char)-a_sign;
		unsigned char b = (i < b_size) ? b_data[i] : (unsigned char)-b_sign;
		if (a < b) {
			return -1;
		}
		if (b < a) {
			return 1;
		}
	}
	return 0;
}

#endif

test.c

#include <limits.h>
#include <stdio.h>

#define TEST(X, ...) \
	printf("%s %c %s\n", #X, "<=>"[meta_int_cmp((X), (__VA_ARGS__)) + 1], #__VA_ARGS__)

int main() {
	TEST(0, 0);
	TEST(1, 0);
	TEST(0, 1);

	TEST(-1, 0);
	TEST(-5, 5u);
	TEST(5u, -5);

	TEST(INT_MIN, (unsigned)INT_MIN);
	TEST((char)0, 0ull);
	TEST((char)0, ULLONG_MAX);
	TEST(LLONG_MAX, (ULLONG_MAX >> 1));
	TEST(SCHAR_MIN, LLONG_MIN);
}