Provide BitField64 utility class.

test/cctest/test-conversions.cc

Index: test/cctest/test-conversions.cc
diff --git a/test/cctest/test-conversions.cc b/test/cctest/test-conversions.cc
index 651dc59d5845f308e3eb5219872e06e4907c6276..398e832607bae9a58ba6e710025ea64fbd420f2d 100644
--- a/test/cctest/test-conversions.cc
+++ b/test/cctest/test-conversions.cc
@@ -249,15 +249,13 @@ TEST(ExponentNumberStr) {
   CHECK_EQ(1e-106, StringToDouble(&uc, ".000001e-100", NO_FLAGS));
 }
 
-class OneBit1: public BitField<uint32_t, 0, 1> {};
-class OneBit2: public BitField<uint32_t, 7, 1> {};
-class EightBit1: public BitField<uint32_t, 0, 8> {};
-class EightBit2: public BitField<uint32_t, 13, 8> {};
 
 TEST(BitField) {
   uint32_t x;
 
   // One bit bit field can hold values 0 and 1.
+  class OneBit1: public BitField<uint32_t, 0, 1> {};
+  class OneBit2: public BitField<uint32_t, 7, 1> {};
   CHECK(!OneBit1::is_valid(static_cast<uint32_t>(-1)));
   CHECK(!OneBit2::is_valid(static_cast<uint32_t>(-1)));
   for (int i = 0; i < 2; i++) {
@@ -273,6 +271,8 @@ TEST(BitField) {
   CHECK(!OneBit2::is_valid(2));
 
   // Eight bit bit field can hold values from 0 tp 255.
+  class EightBit1: public BitField<uint32_t, 0, 8> {};
+  class EightBit2: public BitField<uint32_t, 13, 8> {};
   CHECK(!EightBit1::is_valid(static_cast<uint32_t>(-1)));
   CHECK(!EightBit2::is_valid(static_cast<uint32_t>(-1)));
   for (int i = 0; i < 256; i++) {
@@ -286,3 +286,20 @@ TEST(BitField) {
   CHECK(!EightBit1::is_valid(256));
   CHECK(!EightBit2::is_valid(256));
 }
+
+
+TEST(BitField64) {
+  uint64_t x;
+
+  // Test most significant bits.
+  class UpperBits: public BitField64<int, 61, 3> {};
+  x = V8_2PART_UINT64_C(0xE0000000, 00000000);
+  CHECK(x == UpperBits::encode(7));
+  CHECK_EQ(7, UpperBits::decode(x));
+
+  // Test the 32/64-bit boundary bits.
+  class MiddleBits: public BitField64<int, 31, 2> {};
+  x = V8_2PART_UINT64_C(0x00000001, 80000000);
+  CHECK(x == MiddleBits::encode(3));
+  CHECK_EQ(3, MiddleBits::decode(x));
+}