hexo/node_modules/webpack/lib/util/numberHash.js

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/

"use strict";

/**
 * The maximum safe integer value for 32-bit integers.
 * @type {number}
 */
const SAFE_LIMIT = 0x80000000;

/**
 * The maximum safe integer value for 32-bit integers minus one. This is used
 * in the algorithm to ensure that intermediate hash values do not exceed the
 * 32-bit integer limit.
 * @type {number}
 */
const SAFE_PART = SAFE_LIMIT - 1;

/**
 * The number of 32-bit integers used to store intermediate hash values.
 * @type {number}
 */
const COUNT = 4;

/**
 * An array used to store intermediate hash values during the calculation.
 * @type {number[]}
 */
const arr = [0, 0, 0, 0, 0];

/**
 * An array of prime numbers used in the hash calculation.
 * @type {number[]}
 */
const primes = [3, 7, 17, 19];

/**
 * Computes a hash value for the given string and range. This hashing algorithm is a modified
 * version of the [FNV-1a algorithm](https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function).
 * It is optimized for speed and does **not** generate a cryptographic hash value.
 *
 * We use `numberHash` in `lib/ids/IdHelpers.js` to generate hash values for the module identifier. The generated
 * hash is used as a prefix for the module id's to avoid collisions with other modules.
 *
 * @param {string} str The input string to hash.
 * @param {number} range The range of the hash value (0 to range-1).
 * @returns {number} - The computed hash value.
 *
 * @example
 *
 * ```js
 * const numberHash = require("webpack/lib/util/numberHash");
 * numberHash("hello", 1000); // 57
 * numberHash("hello world"); // 990
 * ```
 *
 */
module.exports = (str, range) => {
	/**
	 * Initialize the array with zeros before it is used
	 * to store intermediate hash values.
	 */
	arr.fill(0);
	// For each character in the string
	for (let i = 0; i < str.length; i++) {
		// Get the character code.
		const c = str.charCodeAt(i);

		// For each 32-bit integer used to store the hash value
		// add the character code to the current hash value and multiply by the prime number and
		// add the previous 32-bit integer.
		arr[0] = (arr[0] + c * primes[0] + arr[3]) & SAFE_PART;
		arr[1] = (arr[1] + c * primes[1] + arr[0]) & SAFE_PART;
		arr[2] = (arr[2] + c * primes[2] + arr[1]) & SAFE_PART;
		arr[3] = (arr[3] + c * primes[3] + arr[2]) & SAFE_PART;

		// For each 32-bit integer used to store the hash value
		// XOR the current hash value with the value of the next 32-bit integer.
		arr[0] = arr[0] ^ (arr[arr[0] % COUNT] >> 1);
		arr[1] = arr[1] ^ (arr[arr[1] % COUNT] >> 1);
		arr[2] = arr[2] ^ (arr[arr[2] % COUNT] >> 1);
		arr[3] = arr[3] ^ (arr[arr[3] % COUNT] >> 1);
	}

	if (range <= SAFE_PART) {
		return (arr[0] + arr[1] + arr[2] + arr[3]) % range;
	} else {
		// Calculate the range extension.
		const rangeExt = Math.floor(range / SAFE_LIMIT);

		const sum1 = (arr[0] + arr[2]) & SAFE_PART;
		const sum2 = (arr[0] + arr[2]) % rangeExt;

		return (sum2 * SAFE_LIMIT + sum1) % range;
	}
};