CompressBitmap.java

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);
    }
}