sganggs
01a44cd288
Online co-op browser remake of Arknights' Stronghold Protocol: Alliance (client-simulated combat, official waves/bonds/items/strategies, 3D board, facing wheel, operator loadout, official emotes, deployment scripts).
57 lines
1.9 KiB
JavaScript
57 lines
1.9 KiB
JavaScript
// server/sim/rng.js — seeded PRNG (mulberry32) + helpers. The ONLY source of randomness in the sim.
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/**
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* Create a deterministic PRNG. Returns a function producing floats in [0, 1) with helper methods.
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* @param {number} seed uint32 (any number is coerced)
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*/
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export function createRng(seed = 1) {
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let s = (Number(seed) >>> 0) || 0x9e3779b9;
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const next = () => {
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s = (s + 0x6d2b79f5) >>> 0;
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let t = s;
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t = Math.imul(t ^ (t >>> 15), t | 1);
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t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
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return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
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};
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const rng = () => next();
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/** integer in [0, n) */
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rng.int = (n) => Math.floor(next() * Math.max(0, n));
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/** float in [a, b) */
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rng.range = (a, b) => a + next() * (b - a);
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/** true with probability p */
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rng.chance = (p) => next() < p;
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/** random element (undefined for empty) */
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rng.pick = (arr) => (arr && arr.length ? arr[Math.floor(next() * arr.length)] : undefined);
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/** in-place Fisher–Yates shuffle, returns arr */
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rng.shuffle = (arr) => {
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for (let i = arr.length - 1; i > 0; i--) {
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const j = Math.floor(next() * (i + 1));
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const tmp = arr[i]; arr[i] = arr[j]; arr[j] = tmp;
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}
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return arr;
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};
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/** weighted pick: items with weightFn(item) */
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rng.weighted = (arr, weightFn) => {
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let total = 0;
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for (const x of arr) total += Math.max(0, weightFn(x));
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if (total <= 0) return undefined;
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let r = next() * total;
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for (const x of arr) { r -= Math.max(0, weightFn(x)); if (r < 0) return x; }
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return arr[arr.length - 1];
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};
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/** current internal state (for debugging / hashing) */
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rng.state = () => s;
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return rng;
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}
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/** Derive a child seed deterministically (e.g. per field). */
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export function deriveSeed(seed, salt) {
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let h = (Number(seed) >>> 0) ^ 0x85ebca6b;
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const str = String(salt);
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for (let i = 0; i < str.length; i++) {
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h = Math.imul(h ^ str.charCodeAt(i), 0x9e3779b1);
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h ^= h >>> 13;
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}
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return h >>> 0;
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}
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