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Diffstat (limited to 'src/main/java/org/rschwietzke/FastRandom.java')
| -rw-r--r-- | src/main/java/org/rschwietzke/FastRandom.java | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/src/main/java/org/rschwietzke/FastRandom.java b/src/main/java/org/rschwietzke/FastRandom.java new file mode 100644 index 0000000..2d25d35 --- /dev/null +++ b/src/main/java/org/rschwietzke/FastRandom.java @@ -0,0 +1,76 @@ +/* + * Copyright 2023 The original 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 org.rschwietzke; + +/** + * Ultra-fast pseudo random generator that is not synchronized! + * Don't use anything from Random by inheritance, this will inherit + * a volatile! Not my idea, copyied in parts some demo random + * generator lessons. + * + * @author rschwietzke + * + */ +public class FastRandom { + private long seed; + + public FastRandom() { + this.seed = System.currentTimeMillis(); + } + + public FastRandom(long seed) { + this.seed = seed; + } + + protected int next(int nbits) { + // N.B. Not thread-safe! + long x = this.seed; + x ^= (x << 21); + x ^= (x >>> 35); + x ^= (x << 4); + this.seed = x; + + x &= ((1L << nbits) - 1); + + return (int) x; + } + + /** + * Borrowed from the JDK + * + * @param bound + * @return + */ + public int nextInt(int bound) { + int r = next(31); + int m = bound - 1; + if ((bound & m) == 0) // i.e., bound is a power of 2 + r = (int) ((bound * (long) r) >> 31); + else { + for (int u = r; u - (r = u % bound) + m < 0; u = next(31)) + ; + } + return r; + } + + /** + * Borrowed from the JDK + * @return + */ + public int nextInt() { + return next(32); + } +} |
