dtl-js/src/js/lib/dtl-random.js

Data Transformation Language - JSON templates and data transformation

/* =================================================
 * Copyright (c) 2015-2024 Jay Kuri
 *
 * This file is part of DTL.
 *
 * DTL is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * DTL is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with DTL; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 * =================================================
 */

// This module provides crypto-compatible randomness 
let our_crypto;
if (typeof window === 'undefined' && typeof crypto === 'undefined') {
    our_crypto = require('crypto').webcrypto;
} else {
    our_crypto = crypto;
}

const getRandomValues = our_crypto.getRandomValues.bind(our_crypto); 

// note that a Uint8Array is not strictly an Array
// if you need to push/pop/shift, etc. You should
// use Array.from() on the return value of random_bytes.
function random_bytes(len) {
    let byte_array = new Uint8Array(len);
    getRandomValues(byte_array);
    return byte_array;
}

function random_number_up_to(max) {

    let result;
    let value_array = new Uint32Array(1);
     
    // this looks odd, but is necessary to remove bias that creeps in
    // when our random value is greater than the maximum multiple of max.
    // This cleans that up.
    const max_acceptable_value = Math.floor((0xFFFFFFFF + 1) / max) * max - 1;
    do {
        getRandomValues(value_array);
        result = value_array[0];
    } while (result > max_acceptable_value);

    return result % max;
}

function random_float() {
    const array = new Uint32Array(2);
    getRandomValues(array);

    // Use bitwise operations to combine the two 32-bit integers
    const high = array[0] & 0x1FFFFF; // 21 bits for high part (keeping within 53 bits)
    const low = array[1];
    const combined = (high * 2 ** 32) + low;

    // Normalize to a floating-point number between 0 and 1
    const float = combined / 2 ** 53;
    return float;
}

let random_stuff = {
    "random_number_up_to": random_number_up_to,
    "random_bytes": random_bytes,
    "random_float": random_float
};

module.exports = random_stuff;