For more examples, see example.java or the examples folder.

import java.io.*;

import java.nio.file.*;

import java.util.*;

import java.util.zip.*;

import me.lemire.integercompression.differential.*;

import me.lemire.integercompression.*;

public class CompressBitmap {

public static void main(String[] args) throws IOException {

if(args.length == 0) {

System.out.println("usage: please provide the file name of a bitmap binary file.");

return;

}

System.out.println("loading file "+args[0]+" as a bitmap");

int[] data = fromBitsetFileToArray(args[0]);

System.out.println("Compressing "+data.length+" integers");

int[] compressed = iic.compress(data);

int[] recov = iic.uncompress(compressed);

System.out.println("compressed from "+data.length*4/1024+"KB to "+compressed.length*4/1024+"KB");

System.out.println("ratio: "+Math.round(data.length*1.0/compressed.length));

if(!Arrays.equals(recov,data)) throw new RuntimeException("bug");

long bef,aft;

bef = System.nanoTime();

recov = iic.uncompress(compressed);

aft = System.nanoTime();

System.out.println("decoding speed:"+Math.round(data.length*1000.0/(aft-bef))+" millions of integers per second");

bef = System.nanoTime();

compressed = iic.compress(data);

aft = System.nanoTime();

System.out.println("encoding speed:"+Math.round(data.length*1000.0/(aft-bef))+" millions of integers per second");

System.out.println("note: with a bit of effort, speed can be much higher.");

System.out.println();

zipStats(args[0]);

}

static IntegratedIntCompressor iic = new IntegratedIntCompressor(

new SkippableIntegratedComposition(

new IntegratedBinaryPacking(),

new IntegratedVariableByte()));

public static int[] fromBitsetFileToArray(String filename) throws IOException {

Path path = Paths.get(filename);

byte[] data = Files.readAllBytes(path);

// we determine cardinality

int card = 0;

for(int k = 0 ; k < data.length; ++k) {

int bv = data[k] & 0xFF;

card += Integer.bitCount(bv);

}

int[] answer = new int[card];

int pos = 0;

for(int k = 0 ; k < data.length; ++k) {

int bv = data[k] & 0xFF;

for(int b = 0 ; b < 8; ++b)

if ( ( (bv >> b) & 1 ) == 1) {

answer[pos++] = b + k * 8;

}

}

if(pos != card) throw new RuntimeException("bug");

return answer;

}

public static void zipStats(String filename) throws IOException {

Path path = Paths.get(filename);

byte[] input = Files.readAllBytes(path);

System.out.println("I will try to compress the original bitmap using zip.");

long bef = System.nanoTime();

ByteArrayOutputStream baos = new ByteArrayOutputStream();

ZipOutputStream zos = new ZipOutputStream(baos);

zos.setLevel(9);

ZipEntry entry = new ZipEntry(filename);

entry.setSize(input.length);

zos.putNextEntry(entry);

zos.write(input);

zos.closeEntry();

zos.close();

byte[] result = baos.toByteArray();

long aft = System.nanoTime();

System.out.println("zip encoding speed:"+input.length*1000.0/(aft-bef)+" million of bytes per second");

System.out.println("zip compression ratio at best level : "+input.length * 1.0 / result.length);

}

}

echo "please be patient as I build the library and the example"

mvn -Dmaven.test.skip=true -Dmaven.javadoc.skip=true -f ../../pom.xml package > /dev/null && javac -cp "../../target/*" CompressBitmap.java && java -cp "../../target/*":. CompressBitmap example_bitmap.bin