Fix Double.NextDouble function.

test/cctest/test-double.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 
 #include <stdlib.h>
 
 #include "v8.h"
 
 #include "platform.h"
 #include "cctest.h"
 #include "diy-fp.h"
 #include "double.h"
@@ skipping 184 matching lines @@
   uint64_t max_double64 = V8_2PART_UINT64_C(0x7fefffff, ffffffff);
   diy_fp = Double(max_double64).AsNormalizedDiyFp();
   Double(max_double64).NormalizedBoundaries(&boundary_minus, &boundary_plus);
   CHECK_EQ(diy_fp.e(), boundary_minus.e());
   CHECK_EQ(diy_fp.e(), boundary_plus.e());
   // max-value does not have a significand of the form 2^p (for some p).
   // Therefore its boundaries are at the same distance.
   CHECK(diy_fp.f() - boundary_minus.f() == boundary_plus.f() - diy_fp.f());
   CHECK((1 << 10) == diy_fp.f() - boundary_minus.f());  // NOLINT
 }
+
+
+TEST(NextDouble) {
+  CHECK_EQ(4e-324, Double(0.0).NextDouble());
+  CHECK_EQ(0.0, Double(-0.0).NextDouble());
+  CHECK_EQ(-0.0, Double(-4e-324).NextDouble());
+  Double d0(-4e-324);
+  Double d1(d0.NextDouble());
+  Double d2(d1.NextDouble());
+  CHECK_EQ(-0.0, d1.value());
+  CHECK_EQ(0.0, d2.value());
+  CHECK_EQ(4e-324, d2.NextDouble());
+  CHECK_EQ(-1.7976931348623157e308, Double(-V8_INFINITY).NextDouble());
+  CHECK_EQ(V8_INFINITY,
+           Double(V8_2PART_UINT64_C(0x7fefffff, ffffffff)).NextDouble());
+}