96 lines
2.9 KiB
JavaScript
96 lines
2.9 KiB
JavaScript
/*
|
|
MIT License http://www.opensource.org/licenses/mit-license.php
|
|
Author Tobias Koppers @sokra
|
|
*/
|
|
|
|
"use strict";
|
|
|
|
/**
|
|
* Threshold for switching from 32-bit to 64-bit hashing. This is selected to ensure that the bias towards lower modulo results when using 32-bit hashing is <0.5%.
|
|
* @type {number}
|
|
*/
|
|
const FNV_64_THRESHOLD = 1 << 24;
|
|
|
|
/**
|
|
* The FNV-1a offset basis for 32-bit hash values.
|
|
* @type {number}
|
|
*/
|
|
const FNV_OFFSET_32 = 2166136261;
|
|
/**
|
|
* The FNV-1a prime for 32-bit hash values.
|
|
* @type {number}
|
|
*/
|
|
const FNV_PRIME_32 = 16777619;
|
|
/**
|
|
* The mask for a positive 32-bit signed integer.
|
|
* @type {number}
|
|
*/
|
|
const MASK_31 = 0x7fffffff;
|
|
|
|
/**
|
|
* The FNV-1a offset basis for 64-bit hash values.
|
|
* @type {bigint}
|
|
*/
|
|
const FNV_OFFSET_64 = BigInt("0xCBF29CE484222325");
|
|
/**
|
|
* The FNV-1a prime for 64-bit hash values.
|
|
* @type {bigint}
|
|
*/
|
|
const FNV_PRIME_64 = BigInt("0x100000001B3");
|
|
|
|
/**
|
|
* Computes a 32-bit FNV-1a hash value for the given string.
|
|
* See https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
|
|
* @param {string} str The input string to hash
|
|
* @returns {number} - The computed hash value.
|
|
*/
|
|
function fnv1a32(str) {
|
|
let hash = FNV_OFFSET_32;
|
|
for (let i = 0, len = str.length; i < len; i++) {
|
|
hash ^= str.charCodeAt(i);
|
|
// Use Math.imul to do c-style 32-bit multiplication and keep only the 32 least significant bits
|
|
hash = Math.imul(hash, FNV_PRIME_32);
|
|
}
|
|
// Force the result to be positive
|
|
return hash & MASK_31;
|
|
}
|
|
|
|
/**
|
|
* Computes a 64-bit FNV-1a hash value for the given string.
|
|
* See https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
|
|
* @param {string} str The input string to hash
|
|
* @returns {bigint} - The computed hash value.
|
|
*/
|
|
function fnv1a64(str) {
|
|
let hash = FNV_OFFSET_64;
|
|
for (let i = 0, len = str.length; i < len; i++) {
|
|
hash ^= BigInt(str.charCodeAt(i));
|
|
hash = BigInt.asUintN(64, hash * FNV_PRIME_64);
|
|
}
|
|
return hash;
|
|
}
|
|
|
|
/**
|
|
* 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); // 73
|
|
* numberHash("hello world"); // 72
|
|
* ```
|
|
*/
|
|
module.exports = (str, range) => {
|
|
if (range < FNV_64_THRESHOLD) {
|
|
return fnv1a32(str) % range;
|
|
}
|
|
return Number(fnv1a64(str) % BigInt(range));
|
|
};
|