com.sun.squawk
Class Offset

java.lang.Object
  com.sun.squawk.Offset

public final class Offset
extends Object

The offset type is used by the runtime system and collector to denote the directed distance between two machine addresses. It is used instead of 'int' or 'Object' for coding clarity, machine-portability (it can map to 32 bit and 64 bit integral types) and access to unsigned operations (Java does not have unsigned int types).

This class is known specially by the translator as a SQUAWKPRIMITIVE and programming with it requires adhering to the restrictions implied by this attribute. Some of these constraints are imposed to keep the job of the translator simple. All of these constraints are currently enforced by the translator. The constraints are:

• A local variable slot allocated by javac for a Squawk primitive variable must never be used for a value of any other type (including a different Squawk primitive type). This is required as the translator cannot currently de-multiplex reference type slots into disjoint typed slots. This restriction on javac is achieved by declaring all Squawk primitive local variables at the outer most scope (as javac using lexical based scoping for register allocation liveness).
• A Squawk primitive value of type T cannot be assigned to or compared with values of any other type (including null) than T.
• A Squawk primitive value of type T cannot be passed as a parameter values of any other type than T. For example, you cannot call T.toString(), or String.valueOf(T). The methods of the classes NativeUnsafe and GC have a special permission to allow Squawk primitive values to passed in place of parameters of type Object.

Only the public methods of this class which do not override any of the methods in java.lang.Object will be available in a non-hosted environment. The translator replaces any calls to these methods to native method calls.

This mechanism was largely inspired by the VM_Address class in the Jikes RVM.

Method Summary

Offset	add(int delta) Adds a value to this offset and return the resulting offset.
Offset	bytesToWords() Scales this offset which currently expresses an offset in bytes to express the same offset in words.
boolean	eq(Offset offset2) Determines if this offset is equal to a given offset.
static Offset	fromPrimitive(int value) Casts an offset expressed as the appropriate Java primitive type for the platform (i.e.
boolean	ge(Offset offset2) Determines if this offset is greater than or equal to a given offset.
boolean	gt(Offset offset2) Determines if this offset is greater than a given offset.
int	hashCode() Gets a hashcode value for this offset which is just the value itself.
boolean	isZero() Determines if this offset is 0.
boolean	le(Offset offset2) Determines if this offset is less than or equal to a given offset.
boolean	lt(Offset offset2) Determines if this offset is less than a given offset.
boolean	ne(Offset offset2) Determines if this offset is not equal to a given offset.
Offset	sub(int delta) Subtracts a value from this offset and return the resulting offset.
int	toInt() Casts a value of type Offset into an int.
int	toPrimitive() Casts a value of type Offset into the appropriate Java primitive type for the platform (i.e.
String	toString() Gets a string representation of this offset.
UWord	toUWord() Casts a value of type Offset into a UWord.
Offset	wordsToBytes() Scales this offset which currently expresses an offset in words to express the same offset in bytes.
static Offset	zero() Gets the canonical Offset representation of null.

Methods inherited from class java.lang.Object

equals, getClass, notify, notifyAll, wait, wait, wait

Method Detail

fromPrimitive

public static Offset fromPrimitive(int value)
                            throws NativePragma

Casts an offset expressed as the appropriate Java primitive type for the platform (i.e. int or long) into a value of type Offset.

Parameters:

value - an offset expressed as an int or long

Returns:

the canonical Offset instance for offset

Throws:

NativePragma

toPrimitive

public int toPrimitive()
                throws NativePragma

Casts a value of type Offset into the appropriate Java primitive type for the platform (i.e. int or long). This will cause a fatal error if this cast cannot occur without changing this offset's sign or truncating its magnitude.

Returns:

this Offset value as an int or long

Throws:

NativePragma

toInt

public int toInt()
          throws NativePragma

Casts a value of type Offset into an int. This will cause a fatal error if this offset value cannot be expressed as a signed 32 bit Java int without changing its sign or truncating its magnitude.

Returns:

this Offset value as an int

Throws:

NativePragma

toUWord

public UWord toUWord()
              throws NativePragma

Casts a value of type Offset into a UWord.

Returns:

this Offset value as a UWord

Throws:

NativePragma

zero

public static Offset zero()
                   throws NativePragma

Gets the canonical Offset representation of null.

Returns:

the canonical Offset representation of null

Throws:

NativePragma

add

public Offset add(int delta)
           throws NativePragma

Adds a value to this offset and return the resulting offset.

Parameters:

delta - the signed value to add

Returns:

the result of adding delta to this offset

Throws:

NativePragma

sub

public Offset sub(int delta)
           throws NativePragma

Subtracts a value from this offset and return the resulting offset.

Parameters:

delta - the signed value to subract

Returns:

the result of subtracting delta from this offset

Throws:

NativePragma

wordsToBytes

public Offset wordsToBytes()
                    throws NativePragma

Scales this offset which currently expresses an offset in words to express the same offset in bytes. That is, the value of this offset is multiplied by the number of bytes in a machine word.

Returns:

the scaled up offset

Throws:

NativePragma

bytesToWords

public Offset bytesToWords()
                    throws NativePragma

Scales this offset which currently expresses an offset in bytes to express the same offset in words. That is, the value of this offset is divided by the number of bytes in a machine word. This method should only be called for offsets which are guaranteed to be a muliple of the number of bytes in a machine word.

Returns:

the scaled down offset

Throws:

NativePragma

isZero

public boolean isZero()
               throws NativePragma

Determines if this offset is 0.

Returns:

true if this offset is 0.

Throws:

NativePragma

eq

public boolean eq(Offset offset2)
           throws NativePragma

Determines if this offset is equal to a given offset.

Parameters:

offset2 - the offset to compare this offset against

Returns:

true if this offset is equal to offset2

Throws:

NativePragma

ne

public boolean ne(Offset offset2)
           throws NativePragma

Determines if this offset is not equal to a given offset.

Parameters:

offset2 - the offset to compare this offset against

Returns:

true if this offset is not equal to offset2

Throws:

NativePragma

lt

public boolean lt(Offset offset2)
           throws NativePragma

Determines if this offset is less than a given offset.

Parameters:

offset2 - the offset to compare this offset against

Returns:

true if this offset is less than or equals to offset2

Throws:

NativePragma

le

public boolean le(Offset offset2)
           throws NativePragma

Determines if this offset is less than or equal to a given offset.

Parameters:

offset2 - the offset to compare this offset against

Returns:

true if this offset is less than or equal to offset2

Throws:

NativePragma

gt

public boolean gt(Offset offset2)
           throws NativePragma

Determines if this offset is greater than a given offset.

Parameters:

offset2 - the offset to compare this offset against

Returns:

true if this offset is greater than offset2

Throws:

NativePragma

ge

public boolean ge(Offset offset2)
           throws NativePragma

Determines if this offset is greater than or equal to a given offset.

Parameters:

offset2 - the offset to compare this offset against

Returns:

true if this offset is greater than or equal to offset2

Throws:

NativePragma

hashCode

public int hashCode()
             throws HostedPragma

Gets a hashcode value for this offset which is just the value itself.

Overrides:

hashCode in class Object

Returns:

the value of this offset

Throws:

HostedPragma

See Also:

Object.equals(java.lang.Object), Hashtable

toString

public String toString()
                throws HostedPragma

Gets a string representation of this offset.

Overrides:

toString in class Object

Returns:

String

Throws:

HostedPragma