chunk_lookup.java

import net.minecraft.world.World;
import net.minecraft.world.chunk.Chunk;
import net.minecraft.world.chunk.storage.ExtendedBlockStorage;

class Test {
    void checkBlock(World world, int x, int y, int z) {
        int[] xOffsets = {-8, -8, 8, 8};
        int[] zOffsets = {-8, 8, -8, 8};
        int[] yOffsets = {-8, 8};
        ExtendedBlockStorage[][][] esbs = new ExtendedBlockStorage[2][2][2];
        for (int i = 0; i < 4; i++) {
            if(world.chunkExists((x + xOffsets[i]) >> 4, (z + zOffsets[i]) >> 4))
            {
                Chunk chunk = world.getChunkFromChunkCoords((x + xOffsets[i]) >> 4, (z + zOffsets[i]) >> 4);
                for(int j = 0; i < 2; j++) {
                    esbs[i >> 1][i & 1][j] = chunk.getBlockStorageArrays[(y + yOffsets[j]) >> 4];
                }
            } else {
                for(int j = 0; i < 2; j++) {
                    esbs[i >> 1][i & 1][j] = null;
                }
            }
        }
        for(int ix = x - 8; ix < x + 8; ix++) {
            for(int iy = y; iy < y + 9; iy++) {
                for(int iz = z - 8; iz < z + 8; iz++) {
                    ExtendedBlockStorage esb = 
                        esbs[((x >> 3) & 1) + (ix >> 4) - (x >> 4)]
                            [((z >> 3) & 1) + (iz >> 4) - (z >> 4)]
                            [((y >> 3) & 1) + (iy >> 4) - (y >> 4)];
                    int id = esb.getBlockLSBArray()[(iy & 0xF) << 8 | (iz & 0xF) << 4 | (ix & 0xF)];
                    if(esb.getBlockMSBArray() != null) {
                        id |= esb.getBlockMSBArray().get(ix & 0xF, iy & 0xF, iz & 0xF) << 8;
                    }
                    // do stuff with id
                }
            }
        }
    }
}