net.jqwik.engine.properties.shrinking.BigIntegerShrinker Maven / Gradle / Ivy
package net.jqwik.engine.properties.shrinking;
import java.math.*;
import java.util.*;
import java.util.stream.*;
public class BigIntegerShrinker {
private final BigInteger shrinkingTarget;
public BigIntegerShrinker(BigInteger shrinkingTarget) {
this.shrinkingTarget = shrinkingTarget;
}
public Stream shrink(BigInteger value) {
Set candidates = new LinkedHashSet<>();
BigInteger lower = shrinkingTarget.min(value);
BigInteger higher = shrinkingTarget.max(value);
addFibbonaci(candidates, lower, BigInteger.valueOf(0), BigInteger.valueOf(1), higher);
subFibbonaci(candidates, higher, BigInteger.valueOf(0), BigInteger.valueOf(1), lower);
candidates.add(shrinkingTarget);
candidates.remove(value);
return candidates.stream();
}
private void subFibbonaci(
Set candidates, BigInteger target, BigInteger butLast, BigInteger last, BigInteger border
) {
while (true) {
BigInteger step = butLast.add(last);
BigInteger candidate = target.subtract(step);
if (candidate.compareTo(border) <= 0) {
break;
}
candidates.add(candidate);
butLast = last;
last = step;
}
}
private void addFibbonaci(
Set candidates, BigInteger target, BigInteger butLast, BigInteger last, BigInteger border
) {
while (true) {
BigInteger step = butLast.add(last);
BigInteger candidate = target.add(step);
if (candidate.compareTo(border) >= 0) {
break;
}
candidates.add(candidate);
butLast = last;
last = step;
}
}
}