Fixes StrtodDiyFp bugs

include/rapidjson/internal/diyfp.h

@@ -179,7 +179,7 @@ struct DiyFp {
     static const int kDpExponentBias = 0x3FF + kDpSignificandSize;
     static const int kDpMaxExponent = 0x7FF - kDpExponentBias;
     static const int kDpMinExponent = -kDpExponentBias;
-    static const int kDpDenormalExponent = -kDpExponentBias - 1;
+    static const int kDpDenormalExponent = -kDpExponentBias + 1;
     static const uint64_t kDpExponentMask = RAPIDJSON_UINT64_C2(0x7FF00000, 0x00000000);
     static const uint64_t kDpSignificandMask = RAPIDJSON_UINT64_C2(0x000FFFFF, 0xFFFFFFFF);
     static const uint64_t kDpHiddenBit = RAPIDJSON_UINT64_C2(0x00100000, 0x00000000);

include/rapidjson/internal/ieee754.h

@@ -61,12 +61,12 @@ public:
     uint64_t ToBias() const { return (u & kSignMask) ? ~u + 1 : u | kSignMask; }
 
     static unsigned EffectiveSignificandSize(int order) {
-        if (order >= kDenormalExponent + kSignificandSize)
-            return kSignificandSize;
-        else if (order <= kDenormalExponent)
+        if (order >= -1021)
+            return 53;
+        else if (order <= -1074)
             return 0;
         else
-            return order - kDenormalExponent;
+            return order + 1074;
     }
 
 private:

include/rapidjson/internal/strtod.h

@@ -146,27 +146,29 @@ inline bool StrtodFast(double d, int p, double* result) {
 inline bool StrtodDiyFp(const char* decimals, size_t length, size_t decimalPosition, int exp, double* result) {
     uint64_t significand = 0;
     size_t i = 0;   // 2^64 - 1 = 18446744073709551615, 1844674407370955161 = 0x1999999999999999    
-    for (; i < length && (significand < RAPIDJSON_UINT64_C2(0x19999999, 0x99999999) || decimals[i] <= '4'); i++)
+    for (; i < length; i++) {
+        if (significand >  RAPIDJSON_UINT64_C2(0x19999999, 0x99999999) ||
+            significand == RAPIDJSON_UINT64_C2(0x19999999, 0x99999999) && decimals[i] > '5')
+            break;
         significand = significand * 10 + (decimals[i] - '0');
+    }
     
     if (i < length && decimals[i] >= '5') // Rounding
         significand++;
 
-    DiyFp v(significand, 0);
     size_t remaining = length - i;
-    const int dExp = (int)decimalPosition - (int)i + exp + (int)remaining;
-
     const unsigned kUlpShift = 3;
     const unsigned kUlp = 1 << kUlpShift;
     int error = (remaining == 0) ? 0 : kUlp / 2;
 
+    DiyFp v(significand, 0);
     v = v.Normalize();
     error <<= -v.e;
 
+    const int dExp = (int)decimalPosition - (int)i + exp;
+
     int actualExp;
-    double temp1 = v.ToDouble();
-    v = v * GetCachedPower10(dExp, &actualExp);
-    double temp2 = v.ToDouble();
+    DiyFp cachedPower = GetCachedPower10(dExp, &actualExp);
     if (actualExp != dExp) {
         static const DiyFp kPow10[] = {
             DiyFp(RAPIDJSON_UINT64_C2(0xa0000000, 00000000), -60),  // 10^1
@@ -177,9 +179,13 @@ inline bool StrtodDiyFp(const char* decimals, size_t length, size_t decimalPosit
             DiyFp(RAPIDJSON_UINT64_C2(0xf4240000, 00000000), -44),  // 10^6
             DiyFp(RAPIDJSON_UINT64_C2(0x98968000, 00000000), -40)   // 10^7
         };
-        v = v * kPow10[dExp - actualExp - 1];
+        int adjustment = dExp - actualExp - 1;        
+        v = v * kPow10[adjustment];
+        if (length + adjustment > 19) // has more digits than decimal digits in 64-bit
+            error += kUlp / 2;
     }
-    double temp3 = v.ToDouble();
+
+    v = v * cachedPower;
 
     error += kUlp + (error == 0 ? 0 : 1);
 
@@ -197,9 +203,9 @@ inline bool StrtodDiyFp(const char* decimals, size_t length, size_t decimalPosit
         precisionSize -= scaleExp;
     }
 
+    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;
-    DiyFp rounded(v.f >> precisionSize, v.e + precisionSize);
     if (precisionBits >= halfWay + error)
         rounded.f++;
 

test/unittest/readertest.cpp

@@ -195,7 +195,6 @@ static void TestParseDouble() {
             EXPECT_DOUBLE_EQ(x, h.actual_); \
     }
     
-#if 0
     TEST_DOUBLE(fullPrecision, "0.0", 0.0);
     TEST_DOUBLE(fullPrecision, "1.0", 1.0);
     TEST_DOUBLE(fullPrecision, "-1.0", -1.0);
@@ -216,7 +215,6 @@ static void TestParseDouble() {
     TEST_DOUBLE(fullPrecision, "2.22507e-308", 2.22507e-308);
     TEST_DOUBLE(fullPrecision, "-1.79769e+308", -1.79769e+308);
     TEST_DOUBLE(fullPrecision, "-2.22507e-308", -2.22507e-308);
-#endif
     TEST_DOUBLE(fullPrecision, "4.9406564584124654e-324", 4.9406564584124654e-324); // minimum denormal
     TEST_DOUBLE(fullPrecision, "2.2250738585072009e-308", 2.2250738585072009e-308); // Max subnormal double
     TEST_DOUBLE(fullPrecision, "2.2250738585072014e-308", 2.2250738585072014e-308); // Min normal positive double
@@ -259,7 +257,7 @@ static void TestParseDouble() {
         TEST_DOUBLE(fullPrecision, n1e308, 1E308);
     }
 
-#if 0
+#if 1
     static const unsigned count = 10000000;
     // Random test for double
     {