BloomSHA1 (Javadocs [I2P+ 2.13.0+] - API Version 0.9.70+)

java.lang.Object
- org.xlattice.crypto.filters.BloomSHA1

```
public class BloomSHA1
extends Object
```
A Bloom filter for sets of SHA1 digests. A Bloom filter uses a set of k hash functions to determine set membership. Each hash function produces a value in the range 0..M-1. The filter is of size M. To add a member to the set, apply each function to the new member and set the corresponding bit in the filter. For M very large relative to k, this will normally set k bits in the filter. To check whether x is a member of the set, apply each of the k hash functions to x and check whether the corresponding bits are set in the filter. If any are not set, x is definitely not a member. If all are set, x may be a member. The probability of error (the false positive rate) is f = (1 - e^(-kN/M))^k, where N is the number of set members. This class takes advantage of the fact that SHA1 digests are good- quality pseudo-random numbers. The k hash functions are the values of distinct sets of bits taken from the 20-byte SHA1 hash. The number of bits in the filter, M, is constrained to be a power of 2; M == 2^m. The number of bits in each hash function may not exceed floor(m/k). This class is designed to be thread-safe, but this has not been exhaustively tested.

Nested Class Summary
Nested Classes
Modifier and Type Class and Description
static class BloomSHA1.FilterKey
Stores the (opaque) bloom filter offsets for reuse.

Nested Classes
Modifier and Type	Class and Description
`static class`	`BloomSHA1.FilterKey` Stores the (opaque) bloom filter offsets for reuse.

Constructor Summary

Constructors
Constructor and Description
`BloomSHA1()` Creates a filter of 2^20 bits with k defaulting to 8.
`BloomSHA1(int m)` Creates a filter of 2^m bits, with the number of 'hash functions" k defaulting to 8.
`BloomSHA1(int m, int k)` Creates a filter with 2^m bits and k 'hash functions', where each hash function is portion of the 160-bit SHA1 hash.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`int`	`capacity()` Returns the number of bits in the filter.
`void`	`clear()` Clears the filter, synchronized.
`double`	`falsePositives()` Calculates the approximate false positive rate for the current number of set members.
`double`	`falsePositives(int n)` Calculates the approximate false positive rate for a given number of set members.
`BloomSHA1.FilterKey`	`getFilterKey(byte[] b, int offset, int len)` Get the bloom filter offsets for reuse.
`void`	`insert(byte[] b)` Add a key to the set represented by the filter.
`void`	`insert(byte[] b, int offset, int len)` Add a key to the set represented by the filter.
`void`	`locked_insert(BloomSHA1.FilterKey fk)` Add the key to the filter.
`void`	`locked_insert(byte[] b)` Add a key to the filter without synchronization.
`void`	`locked_insert(byte[] b, int offset, int len)` Add a key to the filter without synchronization.
`boolean`	`locked_member(BloomSHA1.FilterKey fk)` Is the key in the filter.
`boolean`	`locked_member(byte[] b)` Checks if a key is in the filter without synchronization.
`boolean`	`locked_member(byte[] b, int offset, int len)` Checks if a key is in the filter without synchronization.
`boolean`	`member(byte[] b)` Is a key in the filter.
`boolean`	`member(byte[] b, int offset, int len)` Is a key in the filter.
`void`	`release(BloomSHA1.FilterKey fk)` Releases filter key arrays back to the buffer pool.
`int`	`size()` Returns the number of keys which have been inserted.

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

- Constructor Detail
  - BloomSHA1
```
public BloomSHA1()
```
    Creates a filter of 2^20 bits with k defaulting to 8.
  - BloomSHA1
```
public BloomSHA1(int m)
```
    Creates a filter of 2^m bits, with the number of 'hash functions" k defaulting to 8.
    Parameters:
    m - determines size of filter
  - BloomSHA1
```
public BloomSHA1(int m,
                 int k)
```
    Creates a filter with 2^m bits and k 'hash functions', where each hash function is portion of the 160-bit SHA1 hash.
    Parameters:
    m - determines number of bits in filter
    k - number of hash functions See KeySelector for important restriction on max m and k
- Method Detail
  - capacity
```
public final int capacity()
```
    Returns the number of bits in the filter.
    Returns:
    number of bits in filter
  - clear
```
public void clear()
```
    Clears the filter, synchronized.
  - falsePositives
```
public final double falsePositives()
```
    Calculates the approximate false positive rate for the current number of set members.
    Returns:
    approximate false positive rate
  - falsePositives
```
public final double falsePositives(int n)
```
    Calculates the approximate false positive rate for a given number of set members.
    Parameters:
    n - number of set members
    Returns:
    approximate false positive rate
  - getFilterKey
```
public BloomSHA1.FilterKey getFilterKey(byte[] b,
                                        int offset,
                                        int len)
```
    Get the bloom filter offsets for reuse. Caller should call release(rv) when done with it.
    Parameters:
    b - byte array representing a key (SHA1 digest)
    offset - starting offset in the byte array
    len - number of bytes to use
    Returns:
    filter key containing the offsets
  - insert
```
public void insert(byte[] b)
```
    Add a key to the set represented by the filter. XXX This version does not maintain 4-bit counters, it is not a counting Bloom filter.
    Parameters:
    b - byte array representing a key (SHA1 digest)
  - insert
```
public void insert(byte[] b,
                   int offset,
                   int len)
```
    Add a key to the set represented by the filter. XXX This version does not maintain 4-bit counters, it is not a counting Bloom filter.
    Parameters:
    b - byte array representing a key (SHA1 digest)
    offset - starting offset in the byte array
    len - number of bytes to use
  - locked_insert
```
public void locked_insert(BloomSHA1.FilterKey fk)
```
    Add the key to the filter.
    Parameters:
    fk - filter key containing offsets
  - locked_insert
```
public final void locked_insert(byte[] b)
```
    Add a key to the filter without synchronization.
    Parameters:
    b - byte array representing a key (SHA1 digest)
  - locked_insert
```
public final void locked_insert(byte[] b,
                                int offset,
                                int len)
```
    Add a key to the filter without synchronization.
    Parameters:
    b - byte array representing a key (SHA1 digest)
    offset - starting offset in the byte array
    len - number of bytes to use
  - locked_member
```
public boolean locked_member(BloomSHA1.FilterKey fk)
```
    Is the key in the filter.
    Parameters:
    fk - filter key containing offsets
    Returns:
    true if the key is in the filter
  - locked_member
```
public final boolean locked_member(byte[] b)
```
    Checks if a key is in the filter without synchronization.
    Parameters:
    b - byte array representing a key (SHA1 digest)
    Returns:
    true if b is in the filter
  - locked_member
```
public final boolean locked_member(byte[] b,
                                   int offset,
                                   int len)
```
    Checks if a key is in the filter without synchronization.
    Parameters:
    b - byte array representing a key (SHA1 digest)
    offset - starting offset in the byte array
    len - number of bytes to use
    Returns:
    true if b is in the filter
  - member
```
public final boolean member(byte[] b)
```
    Is a key in the filter. External interface, internally synchronized.
    Parameters:
    b - byte array representing a key (SHA1 digest)
    Returns:
    true if b is in the filter
  - member
```
public final boolean member(byte[] b,
                            int offset,
                            int len)
```
    Is a key in the filter. External interface, internally synchronized.
    Parameters:
    b - byte array representing a key (SHA1 digest)
    offset - starting offset in the byte array
    len - number of bytes to use
    Returns:
    true if b is in the filter
  - release
```
public void release(BloomSHA1.FilterKey fk)
```
    Releases filter key arrays back to the buffer pool.
    Parameters:
    fk - filter key to release
  - size
```
public final int size()
```
    Returns the number of keys which have been inserted. This class (BloomSHA1) does not guarantee uniqueness in any sense; if the same key is added N times, the number of set members reported will increase by N.
    Returns:
    number of set members

Class BloomSHA1

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

BloomSHA1

BloomSHA1

BloomSHA1

Method Detail

capacity

clear

falsePositives

falsePositives

getFilterKey

insert

insert

locked_insert

locked_insert

locked_insert

locked_member

locked_member

locked_member

member

member

release

size