Fix Integer Overflow #2357 (#2400)

* Fix integer overflow https://github.com/microsoft/LightGBM/issues/2357

* Use 2 spaces not 4

* Move constant the config.h
Move check outside the max_depth check

* Move the max leaves check to config.h

* Remove unnecessary check

docs/Parameters.rst

@@ -135,7 +135,7 @@ Core Parameters
 
    -  in ``dart``, it also affects on normalization weights of dropped trees
 
--  ``num_leaves`` :raw-html:`<a id="num_leaves" title="Permalink to this parameter" href="#num_leaves">&#x1F517;&#xFE0E;</a>`, default = ``31``, type = int, aliases: ``num_leaf``, ``max_leaves``, ``max_leaf``, constraints: ``num_leaves > 1``
+-  ``num_leaves`` :raw-html:`<a id="num_leaves" title="Permalink to this parameter" href="#num_leaves">&#x1F517;&#xFE0E;</a>`, default = ``31``, type = int, aliases: ``num_leaf``, ``max_leaves``, ``max_leaf``, constraints: ``1 < num_leaves <= 131072``
 
    -  max number of leaves in one tree
 

include/LightGBM/config.h

@@ -166,6 +166,7 @@ struct Config {
   // default = 31
   // alias = num_leaf, max_leaves, max_leaf
   // check = >1
+  // check = <=131072
   // desc = max number of leaves in one tree
   int num_leaves = kDefaultNumLeaves;
 

src/io/config.cpp

@@ -320,12 +320,16 @@ void Config::CheckParamConflict() {
   }
   // Check max_depth and num_leaves
   if (max_depth > 0) {
-    int full_num_leaves = static_cast<int>(std::pow(2, max_depth));
+    double full_num_leaves = std::pow(2, max_depth);
     if (full_num_leaves > num_leaves
         && num_leaves == kDefaultNumLeaves) {
       Log::Warning("Accuracy may be bad since you didn't set num_leaves and 2^max_depth > num_leaves");
     }
-    num_leaves = std::min(num_leaves, 2 << max_depth);
+
+    if (full_num_leaves < num_leaves) {
+      // Fits in an int, and is more restrictive than the current num_leaves
+      num_leaves = static_cast<int>(full_num_leaves);
+    }
   }
 }
 

src/io/config_auto.cpp

@@ -301,6 +301,7 @@ void Config::GetMembersFromString(const std::unordered_map<std::string, std::str
 
   GetInt(params, "num_leaves", &num_leaves);
   CHECK(num_leaves >1);
+  CHECK(num_leaves <=131072);
 
   GetInt(params, "num_threads", &num_threads);