// Copyright 2018 the V8 project authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #ifndef V8_OBJECTS_SMI_H_ #define V8_OBJECTS_SMI_H_ #include "src/common/globals.h" #include "src/objects/heap-object.h" // Has to be the last include (doesn't have include guards): #include "src/objects/object-macros.h" namespace v8 { namespace internal { // Smi represents integer Numbers that can be stored in 31 bits. // Smis are immediate which means they are NOT allocated in the heap. // The ptr_ value has the following format: [31 bit signed int] 0 // For long smis it has the following format: // [32 bit signed int] [31 bits zero padding] 0 // Smi stands for small integer. class Smi : public Object { public: // This replaces the OBJECT_CONSTRUCTORS macro, because Smis are special // in that we want them to be constexprs. constexpr Smi() : Object() {} explicit constexpr Smi(Address ptr) : Object(ptr) { DCHECK(HAS_SMI_TAG(ptr)); } // Returns the integer value. inline int value() const { return Internals::SmiValue(ptr()); } inline Smi ToUint32Smi() { if (value() <= 0) return Smi::FromInt(0); return Smi::FromInt(static_cast<uint32_t>(value())); } // Convert a Smi object to an int. static inline int ToInt(const Object object) { return Smi::cast(object).value(); } // Convert a value to a Smi object. static inline constexpr Smi FromInt(int value) { DCHECK(Smi::IsValid(value)); return Smi(Internals::IntToSmi(value)); } static inline Smi FromIntptr(intptr_t value) { DCHECK(Smi::IsValid(value)); int smi_shift_bits = kSmiTagSize + kSmiShiftSize; return Smi((static_cast<Address>(value) << smi_shift_bits) | kSmiTag); } // Given {value} in [0, 2^31-1], force it into Smi range by changing at most // the MSB (leaving the lower 31 bit unchanged). static inline Smi From31BitPattern(int value) { return Smi::FromInt((value << (32 - kSmiValueSize)) >> (32 - kSmiValueSize)); } template <typename E, typename = typename std::enable_if<std::is_enum<E>::value>::type> static inline Smi FromEnum(E value) { STATIC_ASSERT(sizeof(E) <= sizeof(int)); return FromInt(static_cast<int>(value)); } // Returns whether value can be represented in a Smi. static inline bool constexpr IsValid(intptr_t value) { DCHECK_EQ(Internals::IsValidSmi(value), value >= kMinValue && value <= kMaxValue); return Internals::IsValidSmi(value); } // Compare two Smis x, y as if they were converted to strings and then // compared lexicographically. Returns: // -1 if x < y. // 0 if x == y. // 1 if x > y. // Returns the result (a tagged Smi) as a raw Address for ExternalReference // usage. V8_EXPORT_PRIVATE static Address LexicographicCompare(Isolate* isolate, Smi x, Smi y); DECL_CAST(Smi) // Dispatched behavior. V8_EXPORT_PRIVATE void SmiPrint(std::ostream& os) const; DECL_VERIFIER(Smi) // Since this is a constexpr, "calling" it is just as efficient // as reading a constant. static inline constexpr Smi zero() { return Smi::FromInt(0); } static constexpr int kMinValue = kSmiMinValue; static constexpr int kMaxValue = kSmiMaxValue; // Smi value for filling in not-yet initialized tagged field values with a // valid tagged pointer. A field value equal to this doesn't necessarily // indicate that a field is uninitialized, but an uninitialized field should // definitely equal this value. // // This _has_ to be kNullAddress, so that an uninitialized field value read as // an embedded pointer field is interpreted as nullptr. This is so that // uninitialised embedded pointers are not forwarded to the embedder as part // of embedder tracing (and similar mechanisms), as nullptrs are skipped for // those cases and otherwise the embedder would try to dereference the // uninitialized pointer value. static constexpr Smi uninitialized_deserialization_value() { return Smi(kNullAddress); } }; CAST_ACCESSOR(Smi) } // namespace internal } // namespace v8 #include "src/objects/object-macros-undef.h" #endif // V8_OBJECTS_SMI_H_