Fix some numbers parsed incorrectly

Fix #340

include/rapidjson/internal/strtod.h

@@ -191,8 +191,13 @@ inline bool StrtodDiyFp(const char* decimals, size_t length, size_t decimalPosit
     DiyFp rounded(v.f >> precisionSize, v.e + precisionSize);
     const uint64_t precisionBits = (v.f & ((uint64_t(1) << precisionSize) - 1)) * kUlp;
     const uint64_t halfWay = (uint64_t(1) << (precisionSize - 1)) * kUlp;
-    if (precisionBits >= halfWay + error)
+    if (precisionBits >= halfWay + error) {
         rounded.f++;
+        if (rounded.f & (DiyFp::kDpHiddenBit << 1)) { // rounding overflows mantissa (issue #340)
+            rounded.f >>= 1;
+            rounded.e++;
+        }
+    }
 
     *result = rounded.ToDouble();
 

test/unittest/readertest.cpp

@@ -327,15 +327,44 @@ static void TestParseDouble() {
                 if (fullPrecision) {
                     EXPECT_EQ(d.Uint64Value(), a.Uint64Value());
                     if (d.Uint64Value() != a.Uint64Value())
-                        printf("  String: %sn  Actual: %.17gnExpected: %.17gn", buffer, h.actual_, d.Value());
+                        printf("  String: %s\n  Actual: %.17g\nExpected: %.17g\n", buffer, h.actual_, d.Value());
                 }
                 else {
-                    EXPECT_EQ(d.Sign(), a.Sign()); /* for 0.0 != -0.0 */
+                    EXPECT_EQ(d.Sign(), a.Sign()); // for 0.0 != -0.0
                     EXPECT_DOUBLE_EQ(d.Value(), h.actual_);
                 }
             }
         }
     }
+
+    // Issue #340
+    TEST_DOUBLE(fullPrecision, "7.450580596923828e-9", 7.450580596923828e-9);
+    {
+        internal::Double d(1.0);
+        for (int i = 0; i < 324; i++) {
+            char buffer[32];
+            *internal::dtoa(d.Value(), buffer) = '\0';
+
+            StringStream s(buffer);
+            ParseDoubleHandler h;
+            Reader reader;
+            ASSERT_EQ(kParseErrorNone, reader.Parse<fullPrecision ? kParseFullPrecisionFlag : 0>(s, h).Code());
+            EXPECT_EQ(1u, h.step_);
+            internal::Double a(h.actual_);
+            if (fullPrecision) {
+                EXPECT_EQ(d.Uint64Value(), a.Uint64Value());
+                if (d.Uint64Value() != a.Uint64Value())
+                    printf("  String: %s\n  Actual: %.17g\nExpected: %.17g\n", buffer, h.actual_, d.Value());
+            }
+            else {
+                EXPECT_EQ(d.Sign(), a.Sign()); // for 0.0 != -0.0
+                EXPECT_DOUBLE_EQ(d.Value(), h.actual_);
+            }
+
+
+            d = d.Value() * 0.5;
+        }
+    }
 #undef TEST_DOUBLE
 }