1 files changed, 38 insertions, 25 deletions
diff --git a/JavaScriptCore/runtime/JSValue.cpp b/JavaScriptCore/runtime/JSValue.cpp
index 6db6954..2a23a79 100644
--- a/JavaScriptCore/runtime/JSValue.cpp
+++ b/JavaScriptCore/runtime/JSValue.cpp
@@ -135,36 +135,49 @@ char* JSValue::description()
 }
 #endif
 
-int32_t toInt32SlowCase(double d, bool& ok)
+// This in the ToInt32 operation is defined in section 9.5 of the ECMA-262 spec.
+// Note that this operation is identical to ToUInt32 other than to interpretation
+// of the resulting bit-pattern (as such this metod is also called to implement
+// ToUInt32).
+//
+// The operation can be descibed as round towards zero, then select the 32 least
+// bits of the resulting value in 2s-complement representation.
+int32_t toInt32(double number)
 {
-    if (isnan(d) || isinf(d)) {
-        ok = false;
+    int64_t bits = WTF::bitwise_cast<int64_t>(number);
+    int32_t exp = (static_cast<int32_t>(bits >> 52) & 0x7ff) - 0x3ff;
+
+    // If exponent < 0 there will be no bits to the left of the decimal point
+    // after rounding; if the exponent is > 83 then no bits of precision can be
+    // left in the low 32-bit range of the result (IEEE-754 doubles have 52 bits
+    // of fractional precision).
+    // Note this case handles 0, -0, and all infinte, NaN, & denormal value. 
+    if (exp < 0 || exp > 83)
         return 0;
-    }
-
-    ok = true;
-
-    double d32 = fmod(trunc(d), D32);
-    if (d32 >= D32 / 2)
-        d32 -= D32;
-    else if (d32 < -D32 / 2)
-        d32 += D32;
-    return static_cast<int32_t>(d32);
-}
 
-uint32_t toUInt32SlowCase(double d, bool& ok)
-{
-    if (isnan(d) || isinf(d)) {
-        ok = false;
-        return 0;
+    // Select the appropriate 32-bits from the floating point mantissa.  If the
+    // exponent is 52 then the bits we need to select are already aligned to the
+    // lowest bits of the 64-bit integer representation of tghe number, no need
+    // to shift.  If the exponent is greater than 52 we need to shift the value
+    // left by (exp - 52), if the value is less than 52 we need to shift right
+    // accordingly.
+    int32_t result = (exp > 52)
+        ? static_cast<int32_t>(bits << (exp - 52))
+        : static_cast<int32_t>(bits >> (52 - exp));
+
+    // IEEE-754 double precision values are stored omitting an implicit 1 before
+    // the decimal point; we need to reinsert this now.  We may also the shifted
+    // invalid bits into the result that are not a part of the mantissa (the sign
+    // and exponent bits from the floatingpoint representation); mask these out.
+    if (exp < 32) {
+        int32_t missingOne = 1 << exp;
+        result &= missingOne - 1;
+        result += missingOne;
     }
 
-    ok = true;
-
-    double d32 = fmod(trunc(d), D32);
-    if (d32 < 0)
-        d32 += D32;
-    return static_cast<uint32_t>(d32);
+    // If the input value was negative (we could test either 'number' or 'bits',
+    // but testing 'bits' is likely faster) invert the result appropriately.
+    return bits < 0 ? -result : result;
 }
 
 NEVER_INLINE double nonInlineNaN()