一、前言
关于flink-core源码包中的org.apache.flink.util.MathUtils数学公式工具类,对常用数据公式方法计算等。
二、源码说明
package org.apache.flink.util;@b@@b@ @b@public final class MathUtils {@b@ @b@ @b@ public static int log2floor(int value) throws ArithmeticException {@b@ if (value == 0) {@b@ throw new ArithmeticException("Logarithm of zero is undefined.");@b@ }@b@@b@ return 31 - Integer.numberOfLeadingZeros(value);@b@ }@b@ @b@ /**@b@ * Computes the logarithm of the given value to the base of 2. This method throws an error,@b@ * if the given argument is not a power of 2.@b@ * @b@ * @param value The value to compute the logarithm for.@b@ * @return The logarithm to the base of 2.@b@ * @throws ArithmeticException Thrown, if the given value is zero.@b@ * @throws IllegalArgumentException Thrown, if the given value is not a power of two.@b@ */@b@ public static int log2strict(int value) throws ArithmeticException, IllegalArgumentException {@b@ if (value == 0) {@b@ throw new ArithmeticException("Logarithm of zero is undefined.");@b@ }@b@ if ((value & (value - 1)) != 0) {@b@ throw new IllegalArgumentException("The given value " + value + " is not a power of two.");@b@ }@b@ return 31 - Integer.numberOfLeadingZeros(value);@b@ }@b@ @b@ /**@b@ * Decrements the given number down to the closest power of two. If the argument is a@b@ * power of two, it remains unchanged.@b@ * @b@ * @param value The value to round down.@b@ * @return The closest value that is a power of two and less or equal than the given value.@b@ */@b@ public static int roundDownToPowerOf2(int value) {@b@ return Integer.highestOneBit(value);@b@ }@b@ @b@ /**@b@ * Casts the given value to a 32 bit integer, if it can be safely done. If the cast would change the numeric@b@ * value, this method raises an exception.@b@ * <p>@b@ * This method is a protection in places where one expects to be able to safely case, but where unexpected@b@ * situations could make the cast unsafe and would cause hidden problems that are hard to track down.@b@ * @b@ * @param value The value to be cast to an integer.@b@ * @return The given value as an integer.@b@ * @see Math#toIntExact(long)@b@ */@b@ public static int checkedDownCast(long value) {@b@ int downCast = (int) value;@b@ if (downCast != value) {@b@ throw new IllegalArgumentException("Cannot downcast long value " + value + " to integer.");@b@ }@b@ return downCast;@b@ }@b@@b@ /**@b@ * Checks whether the given value is a power of two.@b@ *@b@ * @param value The value to check.@b@ * @return True, if the value is a power of two, false otherwise.@b@ */@b@ public static boolean isPowerOf2(long value) {@b@ return (value & (value - 1)) == 0;@b@ }@b@@b@ /**@b@ * This function hashes an integer value. It is adapted from Bob Jenkins' website@b@ * <a href="http://www.burtleburtle.net/bob/hash/integer.html">http://www.burtleburtle.net/bob/hash/integer.html</a>.@b@ * The hash function has the <i>full avalanche</i> property, meaning that every bit of the value to be hashed@b@ * affects every bit of the hash value.@b@ *@b@ * It is crucial to use different hash functions to partition data across machines and the internal partitioning of@b@ * data structures. This hash function is intended for partitioning internally in data structures.@b@ *@b@ * @param code The integer to be hashed.@b@ * @return The non-negative hash code for the integer.@b@ */@b@ public static int jenkinsHash(int code) {@b@ code = (code + 0x7ed55d16) + (code << 12);@b@ code = (code ^ 0xc761c23c) ^ (code >>> 19);@b@ code = (code + 0x165667b1) + (code << 5);@b@ code = (code + 0xd3a2646c) ^ (code << 9);@b@ code = (code + 0xfd7046c5) + (code << 3);@b@ code = (code ^ 0xb55a4f09) ^ (code >>> 16);@b@ return code >= 0 ? code : -(code + 1);@b@ }@b@@b@ /**@b@ * This function hashes an integer value.@b@ *@b@ * It is crucial to use different hash functions to partition data across machines and the internal partitioning of@b@ * data structures. This hash function is intended for partitioning across machines.@b@ *@b@ * @param code The integer to be hashed.@b@ * @return The non-negative hash code for the integer.@b@ */@b@ public static int murmurHash(int code) {@b@ code *= 0xcc9e2d51;@b@ code = Integer.rotateLeft(code, 15);@b@ code *= 0x1b873593;@b@@b@ code = Integer.rotateLeft(code, 13);@b@ code = code * 5 + 0xe6546b64;@b@@b@ code ^= 4;@b@ code = bitMix(code);@b@@b@ if (code >= 0) {@b@ return code;@b@ }@b@ else if (code != Integer.MIN_VALUE) {@b@ return -code;@b@ }@b@ else {@b@ return 0;@b@ }@b@ }@b@@b@ /**@b@ * Round the given number to the next power of two@b@ * @param x number to round@b@ * @return x rounded up to the next power of two@b@ */@b@ public static int roundUpToPowerOfTwo(int x) {@b@ x = x - 1;@b@ x |= x >> 1;@b@ x |= x >> 2;@b@ x |= x >> 4;@b@ x |= x >> 8;@b@ x |= x >> 16;@b@ return x + 1;@b@ }@b@@b@ /**@b@ * Pseudo-randomly maps a long (64-bit) to an integer (32-bit) using some bit-mixing for better distribution.@b@ *@b@ * @param in the long (64-bit)input.@b@ * @return the bit-mixed int (32-bit) output@b@ */@b@ public static int longToIntWithBitMixing(long in) {@b@ in = (in ^ (in >>> 30)) * 0xbf58476d1ce4e5b9L;@b@ in = (in ^ (in >>> 27)) * 0x94d049bb133111ebL;@b@ in = in ^ (in >>> 31);@b@ return (int) in;@b@ }@b@@b@ /**@b@ * Bit-mixing for pseudo-randomization of integers (e.g., to guard against bad hash functions). Implementation is@b@ * from Murmur's 32 bit finalizer.@b@ *@b@ * @param in the input value@b@ * @return the bit-mixed output value@b@ */@b@ public static int bitMix(int in) {@b@ in ^= in >>> 16;@b@ in *= 0x85ebca6b;@b@ in ^= in >>> 13;@b@ in *= 0xc2b2ae35;@b@ in ^= in >>> 16;@b@ return in;@b@ }@b@@b@ // ============================================================================================@b@ @b@ /**@b@ * Prevent Instantiation through private constructor.@b@ */@b@ private MathUtils() {}@b@}