Smalltalk80LanguageImplementation:Chapter 27 - Revision history

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	==~~From~~ of the Specification==		==Form of the Specification==

	Two class descriptions named Interpreter and ObjectMemory make up the formal specification of the Smalltalk-80 virtual machine. The implementation of Interpreter will be presented in detail in this chapter and the following two; the implementation of ObjectMemory in Chapter 30.		Two class descriptions named Interpreter and ObjectMemory make up the formal specification of the Smalltalk-80 virtual machine. The implementation of Interpreter will be presented in detail in this chapter and the following two; the implementation of ObjectMemory in Chapter 30.
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	As described in Chapter 26, integers between -16384 and 16383 are encoded directly as object pointers with a 1 in the low-order bit position and the appropriate 2's complement value stored in the high-order 15 bits. These objects are instances of class SmallInteger. A SmallInteger's value, which would ordinarily be stored in a field, is actually determined from its object pointer. So instead of storing a value into a SmallInteger's field, the interpreter must request the object pointer of a SmallInteger with the desired value (using the integerObjectOf: routine). And instead of fetching the value from a field, it must request the value associated with the object pointer (using the integerValueOf: routine). There are also two routines that determine whether an object pointer refers to a SmallInteger (isIntegerObject:) and whether a value is in the right range to be represented as a SmallInteger (isIntegerValue:). The function of the isIntegerObject: routine can also be performed by requesting the class of the object and seeing if it is SmallInteger.		As described in Chapter 26, integers between -16384 and 16383 are encoded directly as object pointers with a 1 in the low-order bit position and the appropriate 2's complement value stored in the high-order 15 bits. These objects are instances of class SmallInteger. A SmallInteger's value, which would ordinarily be stored in a field, is actually determined from its object pointer. So instead of storing a value into a SmallInteger's field, the interpreter must request the object pointer of a SmallInteger with the desired value (using the integerObjectOf: routine). And instead of fetching the value from a field, it must request the value associated with the object pointer (using the integerValueOf: routine). There are also two routines that determine whether an object pointer refers to a SmallInteger (isIntegerObject:) and whether a value is in the right range to be represented as a SmallInteger (isIntegerValue:). The function of the isIntegerObject: routine can also be performed by requesting the class of the object and seeing if it is SmallInteger.

	~~<syntaxhighlight lang~~="~~smalltalk~~">		{\| style="border: 1px solid black;"
	integer access		\|- style="color: black; background-color: gray;"
	integerValueOf: objectPointer\|\|Return the value of the instance of SmallInteger whose pointer is objectPointer.		\| colspan="2" \| integer access
	integerObjectOf: value\|\|Return the object pointer for an instance of SmallInteger whose value is value.		\|- style="vertical-align:top;"
	isIntegerObject: objectPointer\|\|Return true if objectPointer is an instance of SmallInteger, false if not.		\|integerValueOf: objectPointer\|\|Return the value of the instance of SmallInteger whose pointer is objectPointer.
	isIntegerValue: value\|\|Return true if value can be represented as an instance of SmallInteger, false if not.		\|- style="vertical-align:top;"
	~~</syntaxhighlight>~~		\|integerObjectOf: value\|\|Return the object pointer for an instance of SmallInteger whose value is value.
			\|- style="vertical-align:top;"
			\|isIntegerObject: objectPointer\|\|Return true if objectPointer is an instance of SmallInteger, false if not.
			\|- style="vertical-align:top;"
			\|isIntegerValue: value\|\|Return true if value can be represented as an instance of SmallInteger, false if not.
			\|}

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2014-05-09T09:46:18Z

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	The routines in the specification will ~~caontain~~ five types of expression.		The routines in the specification will contain five types of expression.

	# Calls on other routines of the interpreter. Since both the invocation and definition of the routine are in Interpreter, they will appear as messages to self.		# Calls on other routines of the interpreter. Since both the invocation and definition of the routine are in Interpreter, they will appear as messages to self.
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	bitAnd: (2 raisedTo: lastBitIndex - firstBitIndex + 1) - 1		bitAnd: (2 raisedTo: lastBitIndex - firstBitIndex + 1) - 1
	highByteOf: anInteger		highByteOf: anInteger
	~~↑setf~~ extractBits: 0 to: 7		↑self extractBits: 0 to: 7
	of: anInteger		of: anInteger
	lowByteOf: anInteger		lowByteOf: anInteger
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	self storeInstructionPointerValue: instructionPointer + 1		self storeInstructionPointerValue: instructionPointer + 1
	inContext: activeContext.		inContext: activeContext.
	self storeStackPointerValue: stackPointer - ~~TempFramestart~~ + 1		self storeStackPointerValue: stackPointer - TempFrameStart + 1
	inContext: activeContext		inContext: activeContext
	</syntaxhighlight>		</syntaxhighlight>
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	ofObject: classPointer		ofObject: classPointer
	isPointers: classPointer		isPointers: classPointer
	\| ~~pintersFlag~~ \|		\| pointersFlag \|
	pointersFlag ← self extractBits: 0 to: 0		pointersFlag ← self extractBits: 0 to: 0
	of: (self instanceSpecificationOf: classPointer).		of: (self instanceSpecificationOf: classPointer).
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	Note: the instance specification of CompiledMethod does not accurately reflect the structure of its instances since CompiledMethods are not homogeneous. The instance ~~specificationsays~~ that the instances do not contain pointers and are addressed by bytes. This is true of the bytecode section of a CompiledMethod only. The storage manager needs to know that CompiledMethods are special and actually contain some pointers. For all other classes, the instance specification is accurate.		Note: the instance specification of CompiledMethod does not accurately reflect the structure of its instances since CompiledMethods are not homogeneous. The instance specification says that the instances do not contain pointers and are addressed by bytes. This is true of the bytecode section of a CompiledMethod only. The storage manager needs to know that CompiledMethods are special and actually contain some pointers. For all other classes, the instance specification is accurate.

Onionmixer: SMALLTALK80 Chapter 27 Specification of the Virtual Machine 페이지 추가

2014-05-03T03:07:16Z

SMALLTALK80 Chapter 27 Specification of the Virtual Machine 페이지 추가

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