mirror of https://github.com/webpack/webpack.git
100 lines
3.0 KiB
JavaScript
100 lines
3.0 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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* The maximum safe integer value for 32-bit integers.
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* @type {number}
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*/
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const SAFE_LIMIT = 0x80000000;
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/**
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* The maximum safe integer value for 32-bit integers minus one. This is used
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* in the algorithm to ensure that intermediate hash values do not exceed the
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* 32-bit integer limit.
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* @type {number}
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*/
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const SAFE_PART = SAFE_LIMIT - 1;
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/**
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* The number of 32-bit integers used to store intermediate hash values.
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* @type {number}
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*/
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const COUNT = 4;
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/**
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* An array used to store intermediate hash values during the calculation.
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* @type {number[]}
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*/
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const arr = [0, 0, 0, 0, 0];
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/**
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* An array of prime numbers used in the hash calculation.
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* @type {number[]}
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*/
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const primes = [3, 7, 17, 19];
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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); // 57
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* numberHash("hello world"); // 990
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* ```
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*
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*/
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module.exports = (str, range) => {
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/**
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* Initialize the array with zeros before it is used
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* to store intermediate hash values.
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*/
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arr.fill(0);
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// For each character in the string
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for (let i = 0; i < str.length; i++) {
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// Get the character code.
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const c = str.charCodeAt(i);
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// For each 32-bit integer used to store the hash value
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// add the character code to the current hash value and multiply by the prime number and
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// add the previous 32-bit integer.
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arr[0] = (arr[0] + c * primes[0] + arr[3]) & SAFE_PART;
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arr[1] = (arr[1] + c * primes[1] + arr[0]) & SAFE_PART;
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arr[2] = (arr[2] + c * primes[2] + arr[1]) & SAFE_PART;
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arr[3] = (arr[3] + c * primes[3] + arr[2]) & SAFE_PART;
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// For each 32-bit integer used to store the hash value
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// XOR the current hash value with the value of the next 32-bit integer.
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arr[0] = arr[0] ^ (arr[arr[0] % COUNT] >> 1);
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arr[1] = arr[1] ^ (arr[arr[1] % COUNT] >> 1);
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arr[2] = arr[2] ^ (arr[arr[2] % COUNT] >> 1);
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arr[3] = arr[3] ^ (arr[arr[3] % COUNT] >> 1);
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}
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if (range <= SAFE_PART) {
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return (arr[0] + arr[1] + arr[2] + arr[3]) % range;
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} else {
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// Calculate the range extension.
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const rangeExt = Math.floor(range / SAFE_LIMIT);
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const sum1 = (arr[0] + arr[2]) & SAFE_PART;
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const sum2 = (arr[0] + arr[2]) % rangeExt;
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return (sum2 * SAFE_LIMIT + sum1) % range;
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}
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};
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