/**

 * Convert a single hex-nibble to a byte.

 *

 * @param c The hex-nibble to convert.

 * @return The byte the hex-nibble represents, or -1 if it is not a valid hex-nibble.

 */

static int ConvertHexNibbleToByte(char c)

{

	if (c >= '0' && c <= '9') return c - '0';

	if (c >= 'A' && c <= 'F') return c + 10 - 'A';

	if (c >= 'a' && c <= 'f') return c + 10 - 'a';

	return -1;

}

/**

 * Convert a hex-string to a byte-array, while validating it was actually hex.

 *

 * @param hex The hex-string to convert.

 * @param bytes The byte-array to write the result to.

 *

 * @note The length of the hex-string has to be exactly twice that of the length

 * of the byte-array, otherwise conversion will fail.

 *

 * @return True iff the hex-string was valid and the conversion succeeded.

 */

bool ConvertHexToBytes(std::string_view hex, std::span<uint8_t> bytes)

{

	if (bytes.size() != hex.size() / 2) {

		return false;

	}

	/* Hex-string lengths are always divisible by 2. */

	if (hex.size() % 2 != 0) {

		return false;

	}

	for (size_t i = 0; i < hex.size() / 2; i++) {

		auto hi = ConvertHexNibbleToByte(hex[i * 2]);

		auto lo = ConvertHexNibbleToByte(hex[i * 2 + 1]);

		if (hi < 0 || lo < 0) {

			return false;

		}

		bytes[i] = (hi << 4) | lo;

	}

	return true;

}