numberHash.js
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/*
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;
}
};