Fixes #4718: High CPU usage when using large variable names

2 files changed, 6 insertions, 2 deletions

diff --git a/libdevcore/StringUtils.cpp b/libdevcore/StringUtils.cpp
index 01bdc675..50bf7cce 100644
--- a/libdevcore/StringUtils.cpp
+++ b/libdevcore/StringUtils.cpp
@@ -29,13 +29,16 @@
 using namespace std;
 using namespace dev;
 
-bool dev::stringWithinDistance(string const& _str1, string const& _str2, size_t _maxDistance)
+bool dev::stringWithinDistance(string const& _str1, string const& _str2, size_t _maxDistance, size_t _lenThreshold)
 {
 	if (_str1 == _str2)
 		return true;
 
 	size_t n1 = _str1.size();
 	size_t n2 = _str2.size();
+	if (_lenThreshold > 0 && n1 * n2 > _lenThreshold)
+		return false;
+
 	size_t distance = stringDistance(_str1, _str2);
 
 	// if distance is not greater than _maxDistance, and distance is strictly less than length of both names, they can be considered similar
diff --git a/libdevcore/StringUtils.h b/libdevcore/StringUtils.h
index f05a426b..b02b9d12 100644
--- a/libdevcore/StringUtils.h
+++ b/libdevcore/StringUtils.h
@@ -30,7 +30,8 @@ namespace dev
 {
 
 // Calculates the Damerau–Levenshtein distance between _str1 and _str2 and returns true if that distance is not greater than _maxDistance
-bool stringWithinDistance(std::string const& _str1, std::string const& _str2, size_t _maxDistance);
+// if _lenThreshold > 0 and the product of the strings length is greater than _lenThreshold, the function will return false
+bool stringWithinDistance(std::string const& _str1, std::string const& _str2, size_t _maxDistance, size_t _lenThreshold = 0);
 // Calculates the Damerau–Levenshtein distance between _str1 and _str2
 size_t stringDistance(std::string const& _str1, std::string const& _str2);
 // Return a string having elements of suggestions as quoted, alternative suggestions. e.g. "a", "b" or "c"