0f8399ec88
Replace CDN React/ReactDOM/Babel with local libs; remove Babel and inline scripts Build Tailwind locally, add safelist; switch to assets/tailwind.css Self-host Font Awesome and Inter (CSS + woff2); remove external font CDNs Implement strict CSP (no unsafe-inline/eval; scripts/styles/fonts from self) Extract inline handlers; move PWA scripts to external files Add local QR code generation (qrcode lib) and remove api.qrserver.com Improve SessionTypeSelector visual selection (highlighted background and ring) Keep PWA working with service worker and offline assets Refs: CSP hardening, offline-first, no external dependencies
70 lines
1.9 KiB
JavaScript
70 lines
1.9 KiB
JavaScript
const EXP_TABLE = new Uint8Array(512)
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const LOG_TABLE = new Uint8Array(256)
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/**
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* Precompute the log and anti-log tables for faster computation later
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*
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* For each possible value in the galois field 2^8, we will pre-compute
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* the logarithm and anti-logarithm (exponential) of this value
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*
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* ref {@link https://en.wikiversity.org/wiki/Reed%E2%80%93Solomon_codes_for_coders#Introduction_to_mathematical_fields}
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*/
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;(function initTables () {
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let x = 1
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for (let i = 0; i < 255; i++) {
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EXP_TABLE[i] = x
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LOG_TABLE[x] = i
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x <<= 1 // multiply by 2
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// The QR code specification says to use byte-wise modulo 100011101 arithmetic.
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// This means that when a number is 256 or larger, it should be XORed with 0x11D.
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if (x & 0x100) { // similar to x >= 256, but a lot faster (because 0x100 == 256)
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x ^= 0x11D
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}
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}
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// Optimization: double the size of the anti-log table so that we don't need to mod 255 to
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// stay inside the bounds (because we will mainly use this table for the multiplication of
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// two GF numbers, no more).
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// @see {@link mul}
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for (let i = 255; i < 512; i++) {
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EXP_TABLE[i] = EXP_TABLE[i - 255]
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}
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}())
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/**
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* Returns log value of n inside Galois Field
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*
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* @param {Number} n
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* @return {Number}
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*/
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exports.log = function log (n) {
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if (n < 1) throw new Error('log(' + n + ')')
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return LOG_TABLE[n]
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}
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/**
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* Returns anti-log value of n inside Galois Field
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*
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* @param {Number} n
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* @return {Number}
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*/
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exports.exp = function exp (n) {
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return EXP_TABLE[n]
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}
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/**
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* Multiplies two number inside Galois Field
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*
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* @param {Number} x
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* @param {Number} y
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* @return {Number}
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*/
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exports.mul = function mul (x, y) {
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if (x === 0 || y === 0) return 0
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// should be EXP_TABLE[(LOG_TABLE[x] + LOG_TABLE[y]) % 255] if EXP_TABLE wasn't oversized
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// @see {@link initTables}
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return EXP_TABLE[LOG_TABLE[x] + LOG_TABLE[y]]
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}
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