fix support for zero-terminated backreferences + is_prime test

Author: Hana Dusíková

include/ctre/evaluation.hpp

@@ -380,7 +380,7 @@ constexpr CTRE_FORCE_INLINE R evaluate(const Iterator begin, Iterator current, c
 
 // backreference support (match agains content of iterators)
 template <typename Iterator, typename EndIterator> constexpr CTRE_FORCE_INLINE string_match_result<Iterator> match_against_range(Iterator current, const EndIterator end, Iterator range_current, const Iterator range_end) noexcept {
-	while (current != end && range_current != range_end) {
+	while (end != current && range_end != range_current) {
 		if (*current == *range_current) {
 			current++;
 			range_current++;

tests/is_prime.cpp

@@ -0,0 +1,23 @@
+#include <ctre.hpp>
+
+static constexpr auto pattern = ctll::fixed_string(".?|(..+?)\\g{1}+");
+
+constexpr bool is_prime(std::string_view input) {
+	return !ctre::match<pattern>(input);
+}
+
+int main()
+{
+	static_assert(!is_prime(""));
+	static_assert(!is_prime("a"));
+	static_assert( is_prime("aa"));
+	static_assert( is_prime("aaa"));
+	static_assert(!is_prime("aaaa"));
+	static_assert( is_prime("aaaaa"));
+	static_assert(!is_prime("aaaaaa"));
+	static_assert( is_prime("aaaaaaa"));
+	static_assert(!is_prime("aaaaaaaa"));
+	static_assert(!is_prime("aaaaaaaaa"));
+	static_assert(!is_prime("aaaaaaaaaa"));
+	static_assert( is_prime("aaaaaaaaaaa"));
+}