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/*
* Copyright (C) 2011 The Guava Authors
*
* 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.google.common.math;
import static com.google.common.math.MathBenchmarking.ARRAY_MASK;
import static com.google.common.math.MathBenchmarking.ARRAY_SIZE;
import static com.google.common.math.MathBenchmarking.RANDOM_SOURCE;
import static java.math.RoundingMode.CEILING;
import com.google.caliper.Param;
import com.google.caliper.Runner;
import com.google.caliper.SimpleBenchmark;
import com.google.common.math.BigIntegerMath;
import com.google.common.math.IntMath;
import com.google.common.math.LongMath;
import java.math.BigInteger;
/**
* Benchmarks for the non-rounding methods of {@code BigIntegerMath}.
*
* @author Louis Wasserman
*/
public class BigIntegerMathBenchmark extends SimpleBenchmark {
private static final int[] factorials = new int[ARRAY_SIZE];
private static final int[] slowFactorials = new int[ARRAY_SIZE];
private static final int[] binomials = new int[ARRAY_SIZE];
@Param({"50", "1000", "10000"})
int factorialBound;
@Override
protected void setUp() {
for (int i = 0; i < ARRAY_SIZE; i++) {
factorials[i] = RANDOM_SOURCE.nextInt(factorialBound);
slowFactorials[i] = RANDOM_SOURCE.nextInt(factorialBound);
binomials[i] = RANDOM_SOURCE.nextInt(factorials[i] + 1);
}
}
/**
* Previous version of BigIntegerMath.factorial, kept for timing purposes.
*/
private static BigInteger slowFactorial(int n) {
if (n <= 20) {
return BigInteger.valueOf(LongMath.factorial(n));
} else {
int k = 20;
return BigInteger.valueOf(LongMath.factorial(k)).multiply(slowFactorial(k, n));
}
}
/**
* Returns the product of {@code n1} exclusive through {@code n2} inclusive.
*/
private static BigInteger slowFactorial(int n1, int n2) {
assert n1 <= n2;
if (IntMath.log2(n2, CEILING) * (n2 - n1) < Long.SIZE - 1) {
// the result will definitely fit into a long
long result = 1;
for (int i = n1 + 1; i <= n2; i++) {
result *= i;
}
return BigInteger.valueOf(result);
}
/*
* We want each multiplication to have both sides with approximately the same number of digits.
* Currently, we just divide the range in half.
*/
int mid = (n1 + n2) >>> 1;
return slowFactorial(n1, mid).multiply(slowFactorial(mid, n2));
}
public int timeSlowFactorial(int reps) {
int tmp = 0;
for (int i = 0; i < reps; i++) {
int j = i & ARRAY_MASK;
tmp += slowFactorial(slowFactorials[j]).intValue();
}
return tmp;
}
public int timeFactorial(int reps) {
int tmp = 0;
for (int i = 0; i < reps; i++) {
int j = i & ARRAY_MASK;
tmp += BigIntegerMath.factorial(factorials[j]).intValue();
}
return tmp;
}
public int timeBinomial(int reps) {
int tmp = 0;
for (int i = 0; i < reps; i++) {
int j = i & 0xffff;
tmp += BigIntegerMath.binomial(factorials[j], binomials[j]).intValue();
}
return tmp;
}
public static void main(String[] args) {
Runner.main(BigIntegerMathBenchmark.class, args);
}
}
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