AlignmentEncoding (Jikes RVM API)

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org.jikesrvm.mm.mminterface
Class AlignmentEncoding

java.lang.Object
  org.jikesrvm.mm.mminterface.AlignmentEncoding

public class AlignmentEncoding
extends Object
extends Object

Support for encoding a small amount of metadata in the alignment of a TIB. We choose the alignment of the TIB so that the pointer looks like

     31      24      16      8       0
     +-------+-------+-------+-------+
     xxxxxxxxxxxxxxxxxxxxxxxxxxxxfff00

where the natural alignment of the object is preserved (the low-order bits are zero), and the next least significant n bits contain the encoded metadata.

With the cooperation of MemoryManager, the idea is that we allocate 2^n additional words of memory, then offset the object within the allocated region so that the value of fff is encoded.

The current implementation specifically encodes the TIB pointer, because this is the only pointer field where this technique can give a speedup that makes it worthwhile.

Field Summary
`static int`	`ALIGN_CODE_NONE`
`private static int`	`ALIGNMENT_INCREMENT` How far do we need to shift the object to increment the encoded field by 1
`private static int`	`FIELD_SHIFT` First bit of the encoded field
`(package private) static int`	`FIELD_WIDTH` Bits of metadata that we encode
`private static int`	`MAX_ALIGN_WORDS` Maximum distance (in words) that we shift an object
`private static int`	`TIB_ALIGN_MASK` Bit-mask to select out the encoded field
`private static boolean`	`VERBOSE`

Constructor Summary
`AlignmentEncoding()`

Method Summary
`static Address`	`adjustRegion(int alignCode, Address region)` Adjust a region address so that the object pointer of an object that starts at this address will be aligned so as to encode the specified value.
`(package private) static void`	`assertSanity(int alignCode)` Assert that a prospective encoded value is sane
`static int`	`extractTibCode(Address address)` Extract the encoded value from a TIB pointer, represented as a raw address.
`static int`	`getTibCode(ObjectReference object)` Extract the encoded value from an object's TIB pointer
`private static int`	`getTibCodeForRegion(Address region)`
`static int`	`padding(int alignCode)` Number of padding bytes required.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

ALIGN_CODE_NONE

public static final int ALIGN_CODE_NONE

See Also:: Constant Field Values

FIELD_WIDTH

static final int FIELD_WIDTH

Bits of metadata that we encode

See Also:: Constant Field Values

MAX_ALIGN_WORDS

private static final int MAX_ALIGN_WORDS

Maximum distance (in words) that we shift an object

See Also:: Constant Field Values

FIELD_SHIFT

private static final int FIELD_SHIFT

First bit of the encoded field

See Also:: Constant Field Values

ALIGNMENT_INCREMENT

private static final int ALIGNMENT_INCREMENT

How far do we need to shift the object to increment the encoded field by 1

See Also:: Constant Field Values

TIB_ALIGN_MASK

private static final int TIB_ALIGN_MASK

Bit-mask to select out the encoded field

See Also:: Constant Field Values

VERBOSE

private static final boolean VERBOSE

See Also:: Constant Field Values

Constructor Detail