1// Copyright (C) 2024 The Android Open Source Project 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14 15// Match C++ minstd_rand0 behaviour. 16const MODULUS = 2 ** 31 - 1; 17const MULTIPLIER = 48271; 18const INCREMENT = 1; 19 20// Allow callers to have a private sequence. 21export interface RandState { 22 seed: number; 23} 24 25// If callers don't want to bother maintain their own state, use the global one 26// for the whole app. 27const globalRandState: RandState = {seed: 0}; 28 29// Like math.Rand(), but yields a repeateabled sequence (matters for tests). 30export function pseudoRand(state?: RandState): number { 31 state = state ?? globalRandState; 32 state.seed = (MULTIPLIER * state.seed + INCREMENT) % MODULUS; 33 return state.seed / MODULUS; 34} 35