CatgirlIntelligenceAgency/libraries/btree

BTree

This package contains a small library for creating and reading a static b-tree.

The b-trees are specified through a BTreeContext which contains information about the data and index layout.

Demo

BTreeContext ctx = new BTreeContext(
        4,  // num layers max
        1,  // entry size
        512); // block size bits

        // Allocate a memory area to work in, see the array library for how to do this with files
        LongArray array = LongArray.allocate(8192);

        // Write a btree at offset 123 in the area
        long[] items = new long[400];
        BTreeWriter writer = new BTreeWriter(array, ctx);
        final int offsetInFile = 123;

        long btreeSize = writer.write(offsetInFile, items.length, slice -> {
            // we're *must* write items.length * entry.size words in slice
            // these items must be sorted!!

            for (int i = 0; i < items.length; i++) {
                slice.set(i, items[i]);
            }
        });

        // Read the BTree

        BTreeReader reader = new BTreeReader(array, ctx, offsetInFile);
        reader.findEntry(items[0]);