Class SubSubtraction

Implements binary subtraction for two numbers a, b stored in the same chain.

Computes a new binary number c := a - b and optionally determines whether an overflow occurred, i.e., the result was less than 0.

This procedure requires at least 1 pin and it always uses the "outermost / leftmost" pin when traversing the chain. If an amoebot occurs on the chain multiple times, its predecessor and successor directions must be different for all occurrences.

Usage:

Establish a chain of amoebots such that each amoebot knows its predecessor and successor (except the start and end amoebots). Each amoebot should store a bit a and a bit b.
Initialize using the Init(bool, bool, Direction, Direction) method. You must pass the bits a and b and the two chain directions. The chain start should have no predecessor and the end should have no successor.
Call SetupPinConfig(PinConfiguration) to modify the pin configuration.
Call ActivateSend() in the same round to start the procedure.
After this, call ActivateReceive(), SetupPinConfig(PinConfiguration) and ActivateSend() in this order in every round.
The procedure can be paused after each ActivateReceive() call and resumed by continuing with SetupPinConfig(PinConfiguration) in some future round.
Call IsFinishedSub() after ActivateReceive() to check whether the subtraction is finished. Running another iteration after this, until IsFinishedOverflow() returns true, will make the overflow result available.
The subtraction result c is thereafter available through Bit_C() for each amoebot on the chain.

Inheritance

object

Subroutine

SubSubtraction

Namespace: AS2.Subroutines.BinaryOps

Assembly: .dll

Syntax

public class SubSubtraction : Subroutine

Constructors

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SubSubtraction(Particle, ParticleAttribute<int>)

Declaration

public SubSubtraction(Particle p, ParticleAttribute<int> stateAttr = null)

Parameters

Type	Name	Description
Particle	p
ParticleAttribute<int>	stateAttr

Fields

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bit_A

Declaration

private const int bit_A = 2

Field Value

Type	Description
int

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bit_B

Declaration

private const int bit_B = 3

Field Value

Type	Description
int

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bit_C

Declaration

private const int bit_C = 4

Field Value

Type	Description
int

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bit_FinishedOverflow

Declaration

private const int bit_FinishedOverflow = 12

Field Value

Type	Description
int

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bit_FinishedSub

Declaration

private const int bit_FinishedSub = 11

Field Value

Type	Description
int

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bit_Overflow

Declaration

private const int bit_Overflow = 13

Field Value

Type	Description
int

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state

Declaration

private ParticleAttribute<int> state

Field Value

Type	Description
ParticleAttribute<int>

Methods

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ActivateReceive()

Activation during ActivateBeep() to receive the beeps sent in the last round. Should always be called before SetupPinConfig(PinConfiguration) and ActivateSend(), except in the very first activation, where it should not be called.

Declaration

public void ActivateReceive()

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ActivateSend()

Activation during ActivateBeep() to send the beeps required for this step. Must be called after ActivateReceive() and SetupPinConfig(PinConfiguration).

Declaration

public void ActivateSend()

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Bit_A()

This amoebot's bit of a.

Declaration

public bool Bit_A()

Returns

Type	Description
bool	Whether this amoebot's bit of `a` is equal to `1`.

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Bit_B()

This amoebot's bit of b.

Declaration

public bool Bit_B()

Returns

Type	Description
bool	Whether this amoebot's bit of `b` is equal to `1`.

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Bit_C()

This amoebot's bit of c.

Declaration

public bool Bit_C()

Returns

Type	Description
bool	Whether this amoebot's bit of `c` is equal to `1`.

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GetStateBit(int)

Helper for reading a single bit from the state integer.

Declaration

private bool GetStateBit(int bit)

Parameters

Type	Name	Description
int	bit	The position of the bit.

Returns

Type	Description
bool	The value of the state bit at position `bit`.

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HaveOverflow()

Checks whether an overflow occurred during the subtraction. Should only be called once the procedure has finished completely.

Declaration

public bool HaveOverflow()

Returns

Type	Description
bool	`true` if and only if a carry bit was sent beyond the end of the chain.

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Init(bool, bool, Direction, Direction)

Initializes the subroutine. Must be called by each amoebot on the chain that stores a and b.

Declaration

public void Init(bool a, bool b, Direction predDir, Direction succDir)

Parameters

Type	Name	Description
bool	a	This amoebot's bit of `a`.
bool	b	This amoebot's bit of `b`.
Direction	predDir	The direction of the predecessor. Should be NONE only at the start of the chain.
Direction	succDir	The direction of the successor. Should be NONE only at the end of the chain.

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IsFinishedOverflow()

Checks whether the procedure including overflow detection is finished. Should be called after ActivateReceive().

Declaration

public bool IsFinishedOverflow()

Returns

Type	Description
bool	`true` if and only if the overflow detection procedure has finished.

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IsFinishedSub()

Checks whether the subtraction procedure is finished. Should be called after ActivateReceive(). If an overflow should be detected, another iteration has to be run.

Declaration

public bool IsFinishedSub()

Returns

Type	Description
bool	`true` if and only if the addition procedure has finished.

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PredDir()

Helper for reading the predecessor direction from the state integer.

Declaration

private Direction PredDir()

Returns

Type	Description
Direction	The direction of the chain predecessor.

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Round()

Helper for reading the round number from the state integer.

Declaration

private int Round()

Returns

Type	Description
int	The current round number.

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SetRound(int)

Helper for setting the round counter.

Declaration

private void SetRound(int round)

Parameters

Type	Name	Description
int	round	The new value of the round counter.

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SetStateBit(int, bool)

Helper for setting a single bit from the state integer.

Declaration

private void SetStateBit(int bit, bool value)

Parameters

Type	Name	Description
int	bit	The position of the bit.
bool	value	The new value of the bit.

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SetupPinConfig(PinConfiguration)

Sets up the required circuits for the next step in the given pin configuration. This must be called after ActivateReceive() and before ActivateSend().

Declaration

public void SetupPinConfig(PinConfiguration pc)

Parameters

Type	Name	Description
PinConfiguration	pc	The pin configuration to set up. Partition set IDs will always equal one of the IDs of the contained pins.

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SuccDir()

Helper for reading the successor direction from the state integer.

Declaration

private Direction SuccDir()

Returns

Type	Description
Direction	The direction of the chain successor.