maths_utils: Factor out calculate_odd_parity() with builtins

* swdptap of firmware and "adapter"_swd of `hosted` all used parity/popcount
* Extracting this also allows using MSVC with adapter backends
* Use `uint8_t` to correspond to `hosted` libusb packet buffers

src/include/maths_utils.h

@@ -37,5 +37,6 @@
 #include <stdint.h>
 
 uint8_t ulog2(uint32_t value);
+uint8_t calculate_odd_parity(uint32_t value);
 
 #endif /* INCLUDE_MATHS_UTILS_H */

src/maths_utils.c

@@ -74,3 +74,21 @@ uint8_t ulog2(uint32_t value)
 	return (sizeof(uint8_t) * 8U) - result;
 #endif
 }
+
+uint8_t calculate_odd_parity(const uint32_t value)
+{
+#if defined(__GNUC__)
+	/* Ask for the libgcc impl */
+	return __builtin_parity(value);
+#elif defined(_MSC_VER)
+	/* Ask for a CPU insn */
+	return __popcount(value) & 1U;
+#else
+	/* Generic impl */
+	uint8_t result = 0;
+	for (uint32_t bit = 0; bit < 32; ++bit)
+		result ^= (value >> bit) & 1U;
+
+	return result;
+#endif
+}