@effect-ts/system/Random/PCG/index.js

Effect-TS is a zero dependency set of libraries to write highly productive, purely functional TypeScript at scale.

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.PCGRandom = void 0;
exports.isNothing = isNothing;

// ets_tracing: off
// forked from https://github.com/frptools
// Copyright 2014 Thom Chiovoloni, released under the MIT license.
/// A random number generator based on the basic implementation of the PCG algorithm,
/// as described here: http://www.pcg-random.org/
// Adapted for TypeScript from Thom's original code at https://github.com/thomcc/pcg-random
function isNothing(value) {
  return value === void 0 || value === null;
}

const defaultIncHi = 0x14057b7e;
const defaultIncLo = 0xf767814f;
const MUL_HI = 0x5851f42d >>> 0;
const MUL_LO = 0x4c957f2d >>> 0;
const BIT_53 = 9007199254740992.0;
const BIT_27 = 134217728.0;
/**
 * PCG is a family of simple fast space-efficient statistically good algorithms for random number generation. Unlike
 * many general-purpose RNGs, they are also hard to predict.
 */

class PCGRandom {
  constructor(seedHi, seedLo, incHi, incLo) {
    if (isNothing(seedLo) && isNothing(seedHi)) {
      seedLo = Math.random() * 0xffffffff >>> 0;
      seedHi = 0;
    } else if (isNothing(seedLo)) {
      seedLo = seedHi;
      seedHi = 0;
    }

    if (isNothing(incLo) && isNothing(incHi)) {
      // @ts-expect-error
      incLo = this._state ? this._state[3] : defaultIncLo; // @ts-expect-error

      incHi = this._state ? this._state[2] : defaultIncHi;
    } else if (isNothing(incLo)) {
      incLo = incHi;
      incHi = 0;
    }

    this._state = new Int32Array([0, 0, incHi >>> 0, ((incLo || 0) | 1) >>> 0]);

    this._next();

    add64(this._state, this._state[0], this._state[1], seedHi >>> 0, seedLo >>> 0);

    this._next();

    return this;
  }
  /**
   * @returns A copy of the internal state of this random number generator as a JavaScript Array
   */


  getState() {
    return [this._state[0], this._state[1], this._state[2], this._state[3]];
  }
  /**
   * Restore state previously retrieved using getState()
   */


  setState(state) {
    this._state[0] = state[0];
    this._state[1] = state[1];
    this._state[2] = state[2];
    this._state[3] = state[3] | 1;
  }

  _next() {
    // save current state (what we'll use for this number)
    const oldHi = this._state[0] >>> 0;
    const oldLo = this._state[1] >>> 0; // churn LCG.

    mul64(this._state, oldHi, oldLo, MUL_HI, MUL_LO);
    add64(this._state, this._state[0], this._state[1], this._state[2], this._state[3]); // get least sig. 32 bits of ((oldstate >> 18) ^ oldstate) >> 27

    let xsHi = oldHi >>> 18;
    let xsLo = (oldLo >>> 18 | oldHi << 14) >>> 0;
    xsHi = (xsHi ^ oldHi) >>> 0;
    xsLo = (xsLo ^ oldLo) >>> 0;
    const xorshifted = (xsLo >>> 27 | xsHi << 5) >>> 0; // rotate xorshifted right a random amount, based on the most sig. 5 bits
    // bits of the old state.

    const rot = oldHi >>> 27;
    const rot2 = (-rot >>> 0 & 31) >>> 0;
    return (xorshifted >>> rot | xorshifted << rot2) >>> 0;
  } /// Get a uniformly distributed 32 bit integer between [0, max).


  integer(max) {
    if (!max) {
      return this._next();
    }

    max = max >>> 0;

    if ((max & max - 1) === 0) {
      return this._next() & max - 1; // fast path for power of 2
    }

    let num = 0;
    const skew = (-max >>> 0) % max >>> 0;

    for (num = this._next(); num < skew; num = this._next()) {// this loop will rarely execute more than twice,
      // and is intentionally empty
    }

    return num % max;
  } /// Get a uniformly distributed IEEE-754 double between 0.0 and 1.0, with
  /// 53 bits of precision (every bit of the mantissa is randomized).


  number() {
    const hi = (this._next() & 0x03ffffff) * 1.0;
    const lo = (this._next() & 0x07ffffff) * 1.0;
    return (hi * BIT_27 + lo) / BIT_53;
  }

}

exports.PCGRandom = PCGRandom;

function mul64(out, aHi, aLo, bHi, bLo) {
  let c1 = (aLo >>> 16) * (bLo & 0xffff) >>> 0;
  let c0 = (aLo & 0xffff) * (bLo >>> 16) >>> 0;
  let lo = (aLo & 0xffff) * (bLo & 0xffff) >>> 0;
  let hi = (aLo >>> 16) * (bLo >>> 16) + ((c0 >>> 16) + (c1 >>> 16)) >>> 0;
  c0 = c0 << 16 >>> 0;
  lo = lo + c0 >>> 0;

  if (lo >>> 0 < c0 >>> 0) {
    hi = hi + 1 >>> 0;
  }

  c1 = c1 << 16 >>> 0;
  lo = lo + c1 >>> 0;

  if (lo >>> 0 < c1 >>> 0) {
    hi = hi + 1 >>> 0;
  }

  hi = hi + Math.imul(aLo, bHi) >>> 0;
  hi = hi + Math.imul(aHi, bLo) >>> 0;
  out[0] = hi;
  out[1] = lo;
} // add two 64 bit numbers (given in parts), and store the result in `out`.


function add64(out, aHi, aLo, bHi, bLo) {
  let hi = aHi + bHi >>> 0;
  const lo = aLo + bLo >>> 0;

  if (lo >>> 0 < aLo >>> 0) {
    hi = hi + 1 | 0;
  }

  out[0] = hi;
  out[1] = lo;
}
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