mirror of https://github.com/webpack/webpack.git
101 lines
2.9 KiB
JavaScript
101 lines
2.9 KiB
JavaScript
/*
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MIT License http://www.opensource.org/licenses/mit-license.php
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Author Tobias Koppers @sokra
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*/
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"use strict";
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/**
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* 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%.
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* @type {number}
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*/
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const FNV_64_THRESHOLD = 1 << 24;
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/**
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* The FNV-1a offset basis for 32-bit hash values.
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* @type {number}
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*/
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const FNV_OFFSET_32 = 2166136261;
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/**
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* The FNV-1a prime for 32-bit hash values.
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* @type {number}
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*/
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const FNV_PRIME_32 = 16777619;
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/**
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* The mask for a positive 32-bit signed integer.
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* @type {number}
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*/
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const MASK_31 = 0x7fffffff;
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/**
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* The FNV-1a offset basis for 64-bit hash values.
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* @type {bigint}
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*/
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const FNV_OFFSET_64 = BigInt("0xCBF29CE484222325");
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/**
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* The FNV-1a prime for 64-bit hash values.
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* @type {bigint}
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*/
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const FNV_PRIME_64 = BigInt("0x100000001B3");
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/**
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* Computes a 32-bit FNV-1a hash value for the given string.
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* See https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
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* @param {string} str The input string to hash
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* @returns {number} - The computed hash value.
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*/
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function fnv1a32(str) {
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let hash = FNV_OFFSET_32;
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for (let i = 0, len = str.length; i < len; i++) {
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hash ^= str.charCodeAt(i);
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// Use Math.imul to do c-style 32-bit multiplication and keep only the 32 least significant bits
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hash = Math.imul(hash, FNV_PRIME_32);
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}
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// Force the result to be positive
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return hash & MASK_31;
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}
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/**
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* Computes a 64-bit FNV-1a hash value for the given string.
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* See https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
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* @param {string} str The input string to hash
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* @returns {bigint} - The computed hash value.
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*/
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function fnv1a64(str) {
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let hash = FNV_OFFSET_64;
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for (let i = 0, len = str.length; i < len; i++) {
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hash ^= BigInt(str.charCodeAt(i));
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hash = BigInt.asUintN(64, hash * FNV_PRIME_64);
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}
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return hash;
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}
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/**
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* Computes a hash value for the given string and range. This hashing algorithm is a modified
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* version of the [FNV-1a algorithm](https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function).
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* It is optimized for speed and does **not** generate a cryptographic hash value.
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*
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* We use `numberHash` in `lib/ids/IdHelpers.js` to generate hash values for the module identifier. The generated
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* hash is used as a prefix for the module id's to avoid collisions with other modules.
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*
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* @param {string} str The input string to hash.
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* @param {number} range The range of the hash value (0 to range-1).
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* @returns {number} - The computed hash value.
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*
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* @example
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*
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* ```js
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* const numberHash = require("webpack/lib/util/numberHash");
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* numberHash("hello", 1000); // 73
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* numberHash("hello world"); // 72
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* ```
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*
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*/
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module.exports = (str, range) => {
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if (range < FNV_64_THRESHOLD) {
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return fnv1a32(str) % range;
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} else {
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return Number(fnv1a64(str) % BigInt(range));
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}
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};
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