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/**
* Copyright 2012-2015 Niall Gallagher
*
* Licensed under 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 com.googlecode.cqengine.quantizer;
/**
* A static factory for creating {@link Quantizer}s for {@link Float} attributes.
*
* See {@link #withCompressionFactor(int)} for details.
*
* @author Niall Gallagher
*/
public class FloatQuantizer {
/**
* Private constructor, not used.
*/
FloatQuantizer() {
}
static class TruncatingAndCompressingQuantizer implements Quantizer {
private final int compressionFactor;
public TruncatingAndCompressingQuantizer(int compressionFactor) {
if (compressionFactor < 2) {
throw new IllegalArgumentException("Invalid compression factor, must be >= 2: " + compressionFactor);
}
this.compressionFactor = compressionFactor;
}
@Override
public Float getQuantizedValue(Float attributeValue) {
return (float) ((attributeValue.longValue() / compressionFactor) * compressionFactor);
}
}
static class TruncatingQuantizer implements Quantizer {
@Override
public Float getQuantizedValue(Float attributeValue) {
return (float) (long) attributeValue.doubleValue();
}
}
/**
* Returns a {@link Quantizer} which converts the input value to the nearest multiple of the compression
* factor, in the direction towards zero.
*
* Examples (compression factor 5):
*
* - Input value 0.0 -> 0
* - Input value 4.2 -> 0
* - Input value 5.0 -> 5
* - Input value 9.9 -> 5
* - Input value -0.0 -> 0
* - Input value -4.2 -> 0
* - Input value -5.0 -> -5
* - Input value -9.9 -> -5
*
*
* @param compressionFactor The number of adjacent mathematical integers to coalesce to a single key. Supply a
* factor < 2 to disable compression and simply truncate everything after the decimal point
* @return A {@link Quantizer} which converts the input value to the closest multiple of the compression
* factor, in the direction towards zero
*/
public static Quantizer withCompressionFactor(int compressionFactor) {
return compressionFactor < 2 ? new TruncatingQuantizer() : new TruncatingAndCompressingQuantizer(compressionFactor);
}
}