added test for parsing 0e100

Author: StilesCrisis

include/rapidjson/internal/diyfp.h

@@ -99,6 +99,7 @@ struct DiyFp {
     }
 
     DiyFp Normalize() const {
+        RAPIDJSON_ASSERT(f != 0); // https://stackoverflow.com/a/26809183/291737
 #if defined(_MSC_VER) && defined(_M_AMD64)
         unsigned long index;
         _BitScanReverse64(&index, f);

test/unittest/readertest.cpp

@@ -207,6 +207,7 @@ static void TestParseDouble() {
 
     TEST_DOUBLE(fullPrecision, "0.0", 0.0);
     TEST_DOUBLE(fullPrecision, "-0.0", -0.0); // For checking issue #289
+    TEST_DOUBLE(fullPrecision, "0e100", 0.0); // Normalize() must not invoke __builtin_clzll(0)
     TEST_DOUBLE(fullPrecision, "1.0", 1.0);
     TEST_DOUBLE(fullPrecision, "-1.0", -1.0);
     TEST_DOUBLE(fullPrecision, "1.5", 1.5);