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Fix non-power-of-two random number generation

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Quantum 2020-09-09 13:13:30 -04:00
parent 9154c5210a
commit e157c32f9f
1 changed files with 8 additions and 3 deletions
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9
src/generator.js
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@ -10,6 +10,7 @@ function getWordList (name) {
throw new Error(`Invalid word list: ${name}`) throw new Error(`Invalid word list: ${name}`)
} }
// Only works when the maximum possible value in indices is divisible by list.length.
function getWords (list, indices) { function getWords (list, indices) {
return Array.from(indices).map(index => list[index % list.length]) return Array.from(indices).map(index => list[index % list.length])
} }
@ -18,21 +19,25 @@ function capitalize (string) {
return string[0].toUpperCase() + string.slice(1) return string[0].toUpperCase() + string.slice(1)
} }
// Only works on power-of-two sized lists.
function pickWords (list, number) { function pickWords (list, number) {
const array = new Uint16Array(number) const array = new Uint16Array(number)
window.crypto.getRandomValues(array) window.crypto.getRandomValues(array)
return getWords(list, array) return getWords(list, array)
} }
// Only works when the maximum possible value of index is divisible by choices.length.
function getChar (choices, index) { function getChar (choices, index) {
return choices[index % choices.length] return choices[index % choices.length]
} }
function pickChar (choices) { function pickChar (choices) {
const array = new Uint32Array(1) const array = new Uint32Array(1)
const maxValid = Math.floor(4294967296 / choices.length) * choices.length;
do {
window.crypto.getRandomValues(array) window.crypto.getRandomValues(array)
const index = array[0] } while (array[0] >= maxValid)
return getChar(choices, index) return getChar(choices, array[0])
} }
function generate (options) { function generate (options) {