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With inspiration from other libraries
/*
* Copyright 2018 jshook
* 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 io.virtdata.libbasics.shared.from_long.to_long;
import io.virtdata.annotations.Description;
import io.virtdata.annotations.Example;
import io.virtdata.annotations.ThreadSafeMapper;
import io.virtdata.libbasics.core.lfsrs.MetaShift;
/**
* This function provides a low-overhead shuffling effect without loading
* elements into memory. It uses a bundled dataset of pre-computed
* Galois LFSR shift register configurations, along with a down-sampling
* method to provide amortized virtual shuffling with minimal memory usage.
*
* Essentially, this guarantees that every value in the specified range will
* be seen at least once before the cycle repeats. However, since the order
* of traversal of these values is dependent on the LFSR configuration, some
* orders will appear much more random than others depending on where you
* are in the traversal cycle.
*
* This function *does* yield values that are deterministic.
*/
@ThreadSafeMapper
@Description("Provides virtual shuffling extremely large numbers.")
public class Shuffle extends MetaShift.Func {
private final long max;
private final long min;
private final long size;
@Example({"Shuffle(11,99)","Provide all values between 11 and 98 inclusive, in some order, then repeat"})
public Shuffle(long min, long maxPlusOne) {
this(min, maxPlusOne, Integer.MAX_VALUE);
}
@Example({"Shuffle(11,99,3)","Provide all values between 11 and 98 inclusive, in some different (and repeatable) order, then repeat"})
public Shuffle(long min, long maxPlusOne, int bankSelector) {
super(MetaShift.Masks.forPeriodAndBankModulo((maxPlusOne-min),bankSelector));
this.min = min;
this.max = maxPlusOne;
this.size = (max-min);
}
@Override
public long applyAsLong(long register) {
register = (register % size) +1;
register = super.applyAsLong(register);
while (register>size) {
register = super.applyAsLong(register);
}
register+=min;
return register;
}
}