org.zmpp.vm
Class AbstractInstruction

java.lang.Object
  org.zmpp.vm.AbstractInstruction

All Implemented Interfaces:

Instruction

Direct Known Subclasses:

LongInstruction, PrintLiteralInstruction, Short0Instruction, Short1Instruction, VariableInstruction

public abstract class AbstractInstruction
extends Object
implements Instruction

This class represents can be considered as a mutable value object, which basically stores an instruction's information in order to restrict the Instruction class's responsibility to executing logic. This information will be incrementally added by the decoder, therefore there are setter methods to add information.

Version:

1.0

Author:

Wei-ju Wu

Nested Class Summary

static class	AbstractInstruction.InstructionForm The available instruction forms.
static class	AbstractInstruction.OperandCount The available operand count types.

Field Summary

static short	FALSE The constant for false.
static short	TRUE The constant for true.

Constructor Summary

AbstractInstruction(Machine machineState, int opcode)
Constructor.

Method Summary

void	addOperand(Operand operand) Adds an operand to this object.
boolean	branchIfTrue() Returns true if this is a branch condition and the branch is executed if the test condition is true, false otherwise.
protected void	branchOnTest(boolean condition) Performs a branch, depending on the state of the condition flag.
short	getBranchOffset() Returns the branch offset.
abstract AbstractInstruction.InstructionForm	getInstructionForm() Returns the instruction's form.
int	getLength() Returns the instruction's length in bytes.
protected Machine	getMachine() Returns the reference to the machine state.
int	getNumOperands() Returns the number of operands.
int	getOpcode() Returns the instruction's opcode.
Operand	getOperand(int operandNum) Returns the operand at the specified position.
abstract AbstractInstruction.OperandCount	getOperandCount() Returns the instruction's operand count type.
int	getStoreVariable() Returns the instruction's store variable.
int	getUnsignedValue(int operandNum) Retrieves the value of the specified operand as an unsigned 16 bit integer.
short	getValue(int operandNum) Converts the specified value into a signed value, depending on the type of the operand.
boolean	isBranch() Returns true, if this instruction is a branch, false, otherwise.
protected void	nextInstruction() Advances the program counter to the next instruction.
protected void	returnFromRoutine(short returnValue) This function returns from the current routine, setting the return value into the specified return variable.
void	setBranchIfTrue(boolean flag) Sets the branch if condition true flag.
void	setBranchOffset(short offset) Sets the branch offset.
void	setLength(int length) Sets the instruction's length in bytes.
void	setOpcode(int opcode) Sets the instruction's opcode.
void	setStoreVariable(int var) Sets the store variable.
protected void	storeResult(short value) Stores the specified value in the result variable.
boolean	storesResult() Returns true, if this instruction stores a result, false, otherwise.
protected void	throwInvalidOpcode() Halt the virtual machine with an error message about this instruction.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.zmpp.vm.Instruction

execute

Field Detail

FALSE

public static final short FALSE

The constant for false.

See Also:

Constant Field Values

TRUE

public static final short TRUE

The constant for true.

See Also:

Constant Field Values

Constructor Detail

AbstractInstruction

public AbstractInstruction(Machine machineState,
                           int opcode)

Constructor.

Parameters:

machineState - a reference to the machine state

opcode - the opcode

Method Detail

getMachine

protected Machine getMachine()

Returns the reference to the machine state.

Returns:

the machine state

getOpcode

public int getOpcode()

Returns the instruction's opcode.

Returns:

the opcode

getInstructionForm

public abstract AbstractInstruction.InstructionForm getInstructionForm()

Returns the instruction's form.

Returns:

the instruction form

getOperandCount

public abstract AbstractInstruction.OperandCount getOperandCount()

Returns the instruction's operand count type.

Returns:

the operand count type

getOperand

public Operand getOperand(int operandNum)

Returns the operand at the specified position.

Parameters:

operandNum - the operand number, starting with 0 as the first operand.

Returns:

the specified operand

getNumOperands

public int getNumOperands()

Returns the number of operands.

Returns:

the number of operands

getStoreVariable

public int getStoreVariable()

Returns the instruction's store variable.

Returns:

the store variable

getBranchOffset

public short getBranchOffset()

Returns the branch offset.

Returns:

the branch offset

getLength

public int getLength()

Returns the instruction's length in bytes.

Returns:

the instruction length

setOpcode

public void setOpcode(int opcode)

Sets the instruction's opcode.

Parameters:

opcode - the opcode

addOperand

public void addOperand(Operand operand)

Adds an operand to this object.

Parameters:

operand - the operand to add

setStoreVariable

public void setStoreVariable(int var)

Sets the store variable.

Parameters:

var - the store variable

setBranchOffset

public void setBranchOffset(short offset)

Sets the branch offset.

Parameters:

offset - the branch offset

setBranchIfTrue

public void setBranchIfTrue(boolean flag)

Sets the branch if condition true flag.

Parameters:

flag - the branch if condition true flag

setLength

public void setLength(int length)

Sets the instruction's length in bytes.

Parameters:

length - the length in bytes

storesResult

public boolean storesResult()

Returns true, if this instruction stores a result, false, otherwise.

Returns:

true if a result is stored, false otherwise

isBranch

public boolean isBranch()

Returns true, if this instruction is a branch, false, otherwise.

Returns:

true if branch, false otherwise

branchIfTrue

public boolean branchIfTrue()

Returns true if this is a branch condition and the branch is executed if the test condition is true, false otherwise.

Returns:

true if the branch is executed on a true test condition

getValue

public short getValue(int operandNum)

Converts the specified value into a signed value, depending on the type of the operand. If the operand is LARGE_CONSTANT or VARIABLE, the value is treated as a 16 bit signed integer, if it is SMALL_CONSTANT, it is treated as an 8 bit signed integer.

Parameters:

operandNum - the operand number

Returns:

a signed value

getUnsignedValue

public int getUnsignedValue(int operandNum)

Retrieves the value of the specified operand as an unsigned 16 bit integer.

Parameters:

operandNum - the operand number

Returns:

the value

storeResult

protected void storeResult(short value)

Stores the specified value in the result variable.

Parameters:

value - the value to store

throwInvalidOpcode

protected void throwInvalidOpcode()

Halt the virtual machine with an error message about this instruction.

nextInstruction

protected void nextInstruction()

Advances the program counter to the next instruction.

branchOnTest

protected void branchOnTest(boolean condition)

Performs a branch, depending on the state of the condition flag. If branchIfConditionTrue is true, the branch will be performed if condition is true, if branchIfCondition is false, the branch will be performed if condition is false.

Parameters:

condition - the test condition

returnFromRoutine

protected void returnFromRoutine(short returnValue)

This function returns from the current routine, setting the return value into the specified return variable.

Parameters:

returnValue - the return value