@woosh/meep-engine/src/core/collection/array/computeStridedArrayHash.js

Pure JavaScript game engine. Fully featured and production ready.

import { assert } from "../../assert.js";

/**
 * Useful for computing hashes of large arrays, can pick a relevant stride and skip large chunks of memory while still capturing good amount of unique information from evenly-spaced areas of the array
 * @template T
 * @param {T[]|Uint32Array|Uint16Array|Uint8Array} array
 * @param {number} offset
 * @param {number} length
 * @param {number} stride
 * @param {function(T):number} elementHash
 * @param {*} [elementHashContext]
 * @return {number}
 */
export function computeStridedArrayHash(
    array, offset, length, stride,
    elementHash, elementHashContext
) {

    assert.isFunction(elementHash, 'elementHash');

    let hash = length;

    for (let i = offset; i < length; i += stride) {
        const value = elementHash.call(elementHashContext, array[i]);

        /**
         * Simple hashing scheme, multiplying existing hash by a prime and adding next value
         * (h<<5) - h ===  h*31
         * @type {number}
         * @ignore
         */
        hash = ((hash << 5) - hash) + value;
    }

    // force uint32
    return hash >>> 0;
}