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statistical encoding

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This commit is contained in:
Arndt 2015-10-11 19:27:33 +02:00
parent f8dee5b7d1
commit ccf6641bad
41 changed files with 4543 additions and 1965 deletions
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238
brouter-util/src/main/java/btools/util/BitCoderContext.java
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@ -1,96 +1,150 @@
package btools.util;
public final class BitCoderContext
public class BitCoderContext
{
private byte[] ab;
private int idx = -1;
private int bm = 0x100; // byte mask
private int b;
public BitCoderContext( byte[] ab )
{
private byte[] ab;
private int idx = -1;
private int bm = 0x100 ; // byte mask
private int b;
public BitCoderContext( byte[] ab )
{
this.ab = ab;
}
// encode a distance with a variable bit length
// (poor mans huffman tree)
// 1 -> 0
// 01 -> 1 + following 1-bit word ( 1..2 )
// 001 -> 3 + following 2-bit word ( 3..6 )
// 0001 -> 7 + following 3-bit word ( 7..14 ) etc.
public void encodeVarBits( int value )
{
int range = 0;
while ( value > range )
{
encodeBit( false );
value -= range+1;
range = 2*range + 1;
}
encodeBit( true );
encode( range, value );
}
// twin to encodeDistance
public int decodeVarBits()
{
int range = 0;
int value = 0;
while ( !decodeBit() )
{
value += range+1;
range = 2*range + 1;
}
return value + decode( range );
}
public void encodeBit( boolean value )
{
if ( bm == 0x100 ) { bm = 1; ab[++idx] = 0; }
if ( value ) ab[idx] |= bm;
bm <<= 1;
}
public boolean decodeBit()
{
if ( bm == 0x100 ) { bm = 1; b = ab[++idx]; }
boolean value = ( (b & bm) != 0 );
bm <<= 1;
return value;
}
// encode a symbol with number of bits according to maxvalue
public void encode( int max, int value )
{
int im = 1; // integer mask
while( max != 0 )
{
if ( bm == 0x100 ) { bm = 1; ab[++idx] = 0; }
if ( (value & im) != 0 ) ab[idx] |= bm;
max >>= 1;
bm <<= 1;
im <<= 1;
}
}
public int getEncodedLength()
{
return idx+1;
}
public int decode( int max )
{
int value = 0;
int im = 1; // integer mask
while( max != 0 )
{
if ( bm == 0x100 ) { bm = 1; b = ab[++idx]; }
if ( (b & bm) != 0 ) value |= im;
max >>= 1;
bm <<= 1;
im <<= 1;
}
return value;
}
this.ab = ab;
}
/**
* encode a distance with a variable bit length
* (poor mans huffman tree)
* 1 -> 0
* 01 -> 1 + following 1-bit word ( 1..2 )
* 001 -> 3 + following 2-bit word ( 3..6 )
* 0001 -> 7 + following 3-bit word ( 7..14 ) etc.
*
* @see #decodeVarBits
*/
public final void encodeVarBits( int value )
{
int range = 0;
while (value > range)
{
encodeBit( false );
value -= range + 1;
range = 2 * range + 1;
}
encodeBit( true );
encodeBounded( range, value );
}
/**
* @see #encodeVarBits
*/
public final int decodeVarBits()
{
int range = 0;
int value = 0;
while (!decodeBit())
{
value += range + 1;
range = 2 * range + 1;
}
return value + decodeBounded( range );
}
public final void encodeBit( boolean value )
{
if ( bm == 0x100 )
{
bm = 1;
ab[++idx] = 0;
}
if ( value )
ab[idx] |= bm;
bm <<= 1;
}
public final boolean decodeBit()
{
if ( bm == 0x100 )
{
bm = 1;
b = ab[++idx];
}
boolean value = ( ( b & bm ) != 0 );
bm <<= 1;
return value;
}
/**
* encode an integer in the range 0..max (inclusive).
* For max = 2^n-1, this just encodes n bits, but in general
* this is variable length encoding, with the shorter codes
* for the central value range
*/
public final void encodeBounded( int max, int value )
{
int im = 1; // integer mask
while (im <= max)
{
if ( bm == 0x100 )
{
bm = 1;
ab[++idx] = 0;
}
if ( ( value & im ) != 0 )
{
ab[idx] |= bm;
max -= im;
}
bm <<= 1;
im <<= 1;
}
}
/**
* decode an integer in the range 0..max (inclusive).
* @see #encodeBounded
*/
public final int decodeBounded( int max )
{
int value = 0;
int im = 1; // integer mask
while (( value | im ) <= max)
{
if ( bm == 0x100 )
{
bm = 1;
b = ab[++idx];
}
if ( ( b & bm ) != 0 )
value |= im;
bm <<= 1;
im <<= 1;
}
return value;
}
/**
* @return the encoded length in bytes
*/
public final int getEncodedLength()
{
return idx + 1;
}
/**
* @return the encoded length in bits
*/
public final long getBitPosition()
{
long bitpos = idx << 3;
int m = bm;
while (m > 1)
{
bitpos++;
m >>= 1;
}
return bitpos;
}
}