SpaceDescriptor (Jikes RVM API)

java.lang.Object
- org.mmtk.utility.heap.SpaceDescriptor

```
public class SpaceDescriptor
extends Object
```
This class manages the encoding and decoding of space descriptors.
Space descriptors are integers that encode a space's mapping into virtual memory. For discontiguous spaces, they indicate discontiguity and mapping must be done by consulting the space map. For contiguous spaces, the space's address range is encoded into the integer (using a fixed point notation).
The purpose of this class is to allow static final int space descriptors to exist for each space, which can then be used in tests to determine whether an object is in a space. A good compiler can perform this decoding at compile time and produce optimal code for the test.

Field Summary

Fields
Modifier and Type	Field and Description
`private static int`	`BASE_EXPONENT`
`private static int`	`DISCONTIG_INDEX_INCREMENT`
`private static int`	`discontiguousSpaceIndex`
`private static int`	`EXPONENT_BITS`
`private static int`	`EXPONENT_MASK`
`private static int`	`EXPONENT_SHIFT`
`private static int`	`MANTISSA_BITS`
`private static int`	`MANTISSA_SHIFT`
`private static int`	`SIZE_BITS`
`private static int`	`SIZE_MASK`
`private static int`	`SIZE_SHIFT`
`private static int`	`TYPE_BITS`
`private static int`	`TYPE_CONTIGUOUS`
`private static int`	`TYPE_CONTIGUOUS_HI`
`private static int`	`TYPE_MASK`
`private static int`	`TYPE_SHARED`

Constructor Summary

Constructors
Constructor and Description

SpaceDescriptor()

Constructors
Constructor and Description
`SpaceDescriptor()`

Method Summary

All Methods Static Methods Concrete Methods
Modifier and Type	Method and Description
`static int`	`createDescriptor()` Create a descriptor for a dis-contiguous (shared) space
`static int`	`createDescriptor(Address start, Address end)` Create a descriptor for a contiguous space
`static int`	`getChunks(int descriptor)`
`static Address`	`getStart(int descriptor)`
`static boolean`	`isContiguous(int descriptor)`
`static boolean`	`isContiguousHi(int descriptor)`

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

- Field Detail
  - TYPE_BITS
```
private static final int TYPE_BITS
```
    See Also:
    
    Constant Field Values
  - TYPE_SHARED
```
private static final int TYPE_SHARED
```
    See Also:
    
    Constant Field Values
  - TYPE_CONTIGUOUS
```
private static final int TYPE_CONTIGUOUS
```
    See Also:
    
    Constant Field Values
  - TYPE_CONTIGUOUS_HI
```
private static final int TYPE_CONTIGUOUS_HI
```
    See Also:
    
    Constant Field Values
  - TYPE_MASK
```
private static final int TYPE_MASK
```
    See Also:
    
    Constant Field Values
  - SIZE_SHIFT
```
private static final int SIZE_SHIFT
```
    See Also:
    
    Constant Field Values
  - SIZE_BITS
```
private static final int SIZE_BITS
```
    See Also:
    
    Constant Field Values
  - SIZE_MASK
```
private static final int SIZE_MASK
```
    See Also:
    
    Constant Field Values
  - EXPONENT_SHIFT
```
private static final int EXPONENT_SHIFT
```
    See Also:
    
    Constant Field Values
  - EXPONENT_BITS
```
private static final int EXPONENT_BITS
```
    See Also:
    
    Constant Field Values
  - EXPONENT_MASK
```
private static final int EXPONENT_MASK
```
    See Also:
    
    Constant Field Values
  - MANTISSA_SHIFT
```
private static final int MANTISSA_SHIFT
```
    See Also:
    
    Constant Field Values
  - MANTISSA_BITS
```
private static final int MANTISSA_BITS
```
    See Also:
    
    Constant Field Values
  - BASE_EXPONENT
```
private static final int BASE_EXPONENT
```
    See Also:
    
    Constant Field Values
  - discontiguousSpaceIndex
```
private static int discontiguousSpaceIndex
```
  - DISCONTIG_INDEX_INCREMENT
```
private static final int DISCONTIG_INDEX_INCREMENT
```
    See Also:
    
    Constant Field Values
- Constructor Detail
  - SpaceDescriptor
```
public SpaceDescriptor()
```
- Method Detail
  - createDescriptor
```
public static int createDescriptor(Address start,
                                   Address end)
```
    Create a descriptor for a contiguous space
    
    Parameters:
    
    start - The start address of the space
    
    end - The end address of the space
    
    Returns:
    
    An integer descriptor encoding the region of virtual memory occupied by the space
  - createDescriptor
```
public static int createDescriptor()
```
    Create a descriptor for a dis-contiguous (shared) space
    
    Returns:
    
    An integer descriptor reflecting the fact that this space is shared (and thus discontiguous and so must be established via maps).
  - isContiguous
```
public static boolean isContiguous(int descriptor)
```
    Parameters:
    
    descriptor - a descriptor for a space
    
    Returns:
    
    true if this descriptor describes a contiguous space
  - isContiguousHi
```
public static boolean isContiguousHi(int descriptor)
```
    Parameters:
    
    descriptor - a descriptor for a space
    
    Returns:
    
    true if this descriptor describes a contiguous space that is at the top of the virtual address space
  - getStart
```
public static Address getStart(int descriptor)
```
    Parameters:
    
    descriptor - a descriptor for a space
    
    Returns:
    
    The start of this region of memory encoded in this descriptor
  - getChunks
```
public static int getChunks(int descriptor)
```
    Parameters:
    
    descriptor - a descriptor for a space
    
    Returns:
    
    The size of the region of memory encoded in this descriptor, in chunks

Class SpaceDescriptor

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

TYPE_BITS

TYPE_SHARED

TYPE_CONTIGUOUS

TYPE_CONTIGUOUS_HI

TYPE_MASK

SIZE_SHIFT

SIZE_BITS

SIZE_MASK

EXPONENT_SHIFT

EXPONENT_BITS

EXPONENT_MASK

MANTISSA_SHIFT

MANTISSA_BITS

BASE_EXPONENT

discontiguousSpaceIndex

DISCONTIG_INDEX_INCREMENT

Constructor Detail

SpaceDescriptor

Method Detail

createDescriptor

createDescriptor

isContiguous

isContiguousHi

getStart

getChunks