ioquatix/geospatial

# Copyright, 2016, by Samuel G. D. Williams. <http://www.codeotaku.com>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
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#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# THE SOFTWARE.

module Geospatial
    module Interleave
        # Convert a Tranpose Hilbert index into a Hilbert integer
        # 15-bit Hilbert integer = A B C D E F G H I J K L M N O is stored
        # as its Transpose:
        # x[0] = A D G J M
        # x[1] = B E H K N
        # x[2] = C F I L O
        #        |--bits-|
        def self.map(index, bits)
            result = 0
            
            index.each_with_index do |x, i|
                offset = index.size - (i+1)
                
                bits.times do |j|
                    result |= (x & 1) << (j*index.size+offset)
                    
                    x >>= 1
                    
                    break if x == 0
                end
            end
            
            return result
        end
        
        def self.unmap(integral, width)
            result = [0] * width
            mask = (1 << width) - 1
            offset = 0
            
            while integral != 0
                # N times, look at each bit and append
                width.times do |i|
                    bit = (integral >> i) & 1
                    result[-1-i] |= bit << offset
                end
                
                # Pop first n bits
                integral >>= width
                
                offset += 1
            end
            
            return result
        end
    end
end