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* Licensed to Elasticsearch under one or more contributor
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* the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.elasticsearch.geometry.utils;
/**
* Utilities for common Bit twiddling methods. Borrowed heavily from Lucene (org.apache.lucene.util.BitUtil).
*/
public class BitUtil { // magic numbers for bit interleaving
private static final long MAGIC[] = {
0x5555555555555555L, 0x3333333333333333L,
0x0F0F0F0F0F0F0F0FL, 0x00FF00FF00FF00FFL,
0x0000FFFF0000FFFFL, 0x00000000FFFFFFFFL,
0xAAAAAAAAAAAAAAAAL
};
// shift values for bit interleaving
private static final short SHIFT[] = {1, 2, 4, 8, 16};
/**
* Interleaves the first 32 bits of each long value
*
* Adapted from: http://graphics.stanford.edu/~seander/bithacks.html#InterleaveBMN
*/
public static long interleave(int even, int odd) {
long v1 = 0x00000000FFFFFFFFL & even;
long v2 = 0x00000000FFFFFFFFL & odd;
v1 = (v1 | (v1 << SHIFT[4])) & MAGIC[4];
v1 = (v1 | (v1 << SHIFT[3])) & MAGIC[3];
v1 = (v1 | (v1 << SHIFT[2])) & MAGIC[2];
v1 = (v1 | (v1 << SHIFT[1])) & MAGIC[1];
v1 = (v1 | (v1 << SHIFT[0])) & MAGIC[0];
v2 = (v2 | (v2 << SHIFT[4])) & MAGIC[4];
v2 = (v2 | (v2 << SHIFT[3])) & MAGIC[3];
v2 = (v2 | (v2 << SHIFT[2])) & MAGIC[2];
v2 = (v2 | (v2 << SHIFT[1])) & MAGIC[1];
v2 = (v2 | (v2 << SHIFT[0])) & MAGIC[0];
return (v2<<1) | v1;
}
/**
* Extract just the even-bits value as a long from the bit-interleaved value
*/
public static long deinterleave(long b) {
b &= MAGIC[0];
b = (b ^ (b >>> SHIFT[0])) & MAGIC[1];
b = (b ^ (b >>> SHIFT[1])) & MAGIC[2];
b = (b ^ (b >>> SHIFT[2])) & MAGIC[3];
b = (b ^ (b >>> SHIFT[3])) & MAGIC[4];
b = (b ^ (b >>> SHIFT[4])) & MAGIC[5];
return b;
}
/**
* flip flops odd with even bits
*/
public static final long flipFlop(final long b) {
return ((b & MAGIC[6]) >>> 1) | ((b & MAGIC[0]) << 1 );
}
}