//使用FastPfor算法将排序了的int数组进行压缩,注意:target数组必须是排序后的数组
public static int[] fastPforEncoder(int[] uncompressed)
{
var codec = new SkippableIntegratedComposition(new IntegratedBinaryPacking(), new IntegratedVariableByte());
var compressed = new int[uncompressed.Length + 1024];
var inputoffset = new IntWrapper(0);
var outputoffset = new IntWrapper(1);
codec.headlessCompress(uncompressed, inputoffset, uncompressed.Length, compressed, outputoffset, new IntWrapper(0));
compressed[0] = uncompressed.Length;
compressed = Arrays.copyOf(compressed, outputoffset.intValue());
return(compressed);
}
public void basicExampleHeadless()
{
int[] data = new int[2342351];
Console.WriteLine("Compressing " + data.Length + " integers in one go using the headless approach");
// data should be sorted for best
// results
for (int k = 0; k < data.Length; ++k)
{
data[k] = k;
}
// Very important: the data is in sorted order!!! If not, you
// will get very poor compression with IntegratedBinaryPacking,
// you should use another CODEC.
// next we compose a CODEC. Most of the processing
// will be done with binary packing, and leftovers will
// be processed using variable byte
SkippableIntegratedComposition codec = new SkippableIntegratedComposition(new IntegratedBinaryPacking(),
new IntegratedVariableByte());
// output vector should be large enough...
int[] compressed = new int[data.Length + 1024];
// compressed might not be large enough in some cases
// if you get java.lang.ArrayIndexOutOfBoundsException, try
// allocating more memory
/**
*
* compressing
*
*/
IntWrapper inputoffset = new IntWrapper(0);
IntWrapper outputoffset = new IntWrapper(1);
compressed[0] = data.Length; // we manually store how many integers we
codec.headlessCompress(data, inputoffset, data.Length, compressed, outputoffset, new IntWrapper(0));
// got it!
// inputoffset should be at data.Length but outputoffset tells
// us where we are...
Console.WriteLine(
"compressed from " + data.Length * 4 / 1024 + "KB to " + outputoffset.intValue() * 4 / 1024 + "KB");
// we can repack the data: (optional)
compressed = Arrays.copyOf(compressed, outputoffset.intValue());
/**
*
* now uncompressing
*
*/
int howmany = compressed[0];// we manually stored the number of
// compressed integers
int[] recovered = new int[howmany];
IntWrapper recoffset = new IntWrapper(0);
codec.headlessUncompress(compressed, new IntWrapper(1), compressed.Length, recovered, recoffset, howmany, new IntWrapper(0));
if (Arrays.equals(data, recovered))
{
Console.WriteLine("data is recovered without loss");
}
else
{
throw new Exception("bug"); // could use assert
}
Console.WriteLine();
}