fix: wrong k condition check

Author: proost

sampling/include/var_opt_sketch_impl.hpp

@@ -145,7 +145,7 @@ var_opt_sketch<T, A>::var_opt_sketch(var_opt_sketch&& other) noexcept :
 template<typename T, typename A>
 var_opt_sketch<T, A>::var_opt_sketch(uint32_t k, resize_factor rf, bool is_gadget, const A& allocator) :
   k_(k), h_(0), m_(0), r_(0), n_(0), total_wt_r_(0.0), rf_(rf), allocator_(allocator) {
-  if (k == 0 || k_ > MAX_K) {
+  if (k < 1 || k_ > MAX_K) {
     throw std::invalid_argument("k must be at least 1 and less than 2^31 - 1");
   }
 

sampling/test/var_opt_sketch_test.cpp

@@ -71,6 +71,7 @@ static void check_if_equal(var_opt_sketch<T, A>& sk1, var_opt_sketch<T, A>& sk2)
 TEST_CASE("varopt sketch: invalid k", "[var_opt_sketch]") {
   REQUIRE_THROWS_AS(var_opt_sketch<int>(0), std::invalid_argument);
   REQUIRE_THROWS_AS(var_opt_sketch<int>(1U << 31), std::invalid_argument); // aka k < 0
+  REQUIRE_THROWS_AS(var_opt_sketch<int>(-1), std::invalid_argument);
 }
 
 TEST_CASE("varopt sketch: bad serialization version", "[var_opt_sketch]") {