manifold/common/util/random.ts

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export const randomString = (length = 12) =>
Math.random()
.toString(16)
.substring(2, length + 2)
export function genHash(str: string) {
// xmur3
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for (let i = 0, h = 1779033703 ^ str.length; i < str.length; i++) {
h = Math.imul(h ^ str.charCodeAt(i), 3432918353)
h = (h << 13) | (h >>> 19)
}
return function () {
h = Math.imul(h ^ (h >>> 16), 2246822507)
h = Math.imul(h ^ (h >>> 13), 3266489909)
return (h ^= h >>> 16) >>> 0
}
}
export function createRNG(seed: string) {
// https://stackoverflow.com/a/47593316/1592933
const gen = genHash(seed)
let [a, b, c, d] = [gen(), gen(), gen(), gen()]
// sfc32
return function () {
a >>>= 0
b >>>= 0
c >>>= 0
d >>>= 0
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let t = (a + b) | 0
a = b ^ (b >>> 9)
b = (c + (c << 3)) | 0
c = (c << 21) | (c >>> 11)
d = (d + 1) | 0
t = (t + d) | 0
c = (c + t) | 0
return (t >>> 0) / 4294967296
}
}
export const shuffle = (array: any[], rand: () => number) => {
for (let i = 0; i < array.length; i++) {
const swapIndex = Math.floor(rand() * (array.length - i))
;[array[i], array[swapIndex]] = [array[swapIndex], array[i]]
}
}