Make class BitField able to use 32 bits of a uint32.
Although algorithmically correct, the compiler would not allow to instantiate a BitField that uses all 32 bits without warnings about a too large shift count. As a consequence we were limited to 31 bit values when using BitField. This happened when instantiating a bitfield BitField<T, shift, size> with [shift=0, size=32] or [shift=31, size=1] or more general any [shift=X, size=32-X] As side-effect of the new implementation the compiler now warns if we ever try instantiating a bitfield with size 0. Review URL: http://codereview.chromium.org/606063 git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3910 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
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@ -518,14 +518,14 @@ class CallFunctionStub: public CodeStub {
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}
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#endif
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// Minor key encoding in 31 bits AAAAAAAAAAAAAAAAAAAAAFI A(rgs)F(lag)I(nloop).
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// Minor key encoding in 32 bits with Bitfield <Type, shift, size>.
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class InLoopBits: public BitField<InLoopFlag, 0, 1> {};
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class FlagBits: public BitField<CallFunctionFlags, 1, 1> {};
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class ArgcBits: public BitField<int, 2, 29> {};
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class ArgcBits: public BitField<int, 2, 32 - 2> {};
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Major MajorKey() { return CallFunction; }
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int MinorKey() {
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// Encode the parameters in a unique 31 bit value.
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// Encode the parameters in a unique 32 bit value.
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return InLoopBits::encode(in_loop_)
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| FlagBits::encode(flags_)
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| ArgcBits::encode(argc_);
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@ -250,7 +250,7 @@ class FrameElement BASE_EMBEDDED {
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class CopiedField: public BitField<bool, 3, 1> {};
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class SyncedField: public BitField<bool, 4, 1> {};
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class NumberInfoField: public BitField<NumberInfo::Type, 5, 3> {};
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class DataField: public BitField<uint32_t, 8, 32 - 9> {};
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class DataField: public BitField<uint32_t, 8, 32 - 8> {};
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friend class VirtualFrame;
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};
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@ -179,7 +179,7 @@ class PropertyDetails BASE_EMBEDDED {
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class TypeField: public BitField<PropertyType, 0, 3> {};
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class AttributesField: public BitField<PropertyAttributes, 3, 3> {};
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class DeletedField: public BitField<uint32_t, 6, 1> {};
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class IndexField: public BitField<uint32_t, 7, 31-7> {};
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class IndexField: public BitField<uint32_t, 7, 32-7> {};
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static const int kInitialIndex = 1;
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private:
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@ -141,7 +141,7 @@ class Result BASE_EMBEDDED {
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class TypeField: public BitField<Type, 0, 2> {};
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class NumberInfoField : public BitField<NumberInfo::Type, 2, 3> {};
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class DataField: public BitField<uint32_t, 5, 32 - 6> {};
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class DataField: public BitField<uint32_t, 5, 32 - 5> {};
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inline void CopyTo(Result* destination) const;
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@ -157,7 +157,9 @@ class BitField {
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// Returns a uint32_t mask of bit field.
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static uint32_t mask() {
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return (1U << (size + shift)) - (1U << shift);
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// To use all bits of a uint32 in a bitfield without compiler warnings we
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// have to compute 2^32 without using a shift count of 32.
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return ((1U << shift) << size) - (1U << shift);
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}
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// Returns a uint32_t with the bit field value encoded.
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@ -168,7 +170,7 @@ class BitField {
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// Extracts the bit field from the value.
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static T decode(uint32_t value) {
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return static_cast<T>((value >> shift) & ((1U << (size)) - 1));
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return static_cast<T>((value & mask()) >> shift);
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}
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};
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