File size: 2,627 Bytes
c126239 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 | /**
* Deterministic PRNG utilities shared by all watermark generators and detectors.
*
* We deliberately do NOT replicate torch's MT19937 / randperm bit-for-bit
* (impractical in JS). A watermark only requires that the generator and the
* detector share the same PRF/PRNG stack. Deviations from the reference
* PyTorch implementations are documented in the README.
*/
const MASK64 = (1n << 64n) - 1n;
/** splitmix64: high-quality 64-bit mixer. Returns the next state and output. */
export function splitmix64(state: bigint): { state: bigint; out: bigint } {
let s = (state + 0x9e3779b97f4a7c15n) & MASK64;
let z = s;
z = ((z ^ (z >> 30n)) * 0xbf58476d1ce4e5b9n) & MASK64;
z = ((z ^ (z >> 27n)) * 0x94d049bb133111ebn) & MASK64;
z = z ^ (z >> 31n);
return { state: s, out: z & MASK64 };
}
/** One-shot 64-bit hash of arbitrary bigint input (stateless). */
export function mix64(x: bigint): bigint {
return splitmix64(x & MASK64).out;
}
/** Combine multiple 64-bit values into one (order-sensitive). */
export function hashCombine(...values: bigint[]): bigint {
let h = 0x51_7c_c1_b7_27_22_0a_95n; // arbitrary non-zero start
for (const v of values) {
h = mix64((h ^ (v & MASK64)) & MASK64);
}
return h;
}
/** Map a 64-bit value to a float in [0, 1) using the top 53 bits. */
export function toUnitFloat(x: bigint): number {
return Number((x & MASK64) >> 11n) / 2 ** 53;
}
/**
* Seedable uniform stream (counter-based on splitmix64).
* Counter-based design means identical seeds yield identical streams
* regardless of platform - this is the "shared base RNG stream" used to
* separate watermark effects from sampling randomness.
*/
export class RandomStream {
private state: bigint;
constructor(seed: bigint | number) {
this.state = mix64(BigInt(seed) & MASK64);
}
/** Next uniform float in [0, 1). */
next(): number {
const { state, out } = splitmix64(this.state);
this.state = state;
return toUnitFloat(out);
}
/** Next 64-bit integer. */
nextU64(): bigint {
const { state, out } = splitmix64(this.state);
this.state = state;
return out;
}
}
/**
* Seeded Fisher-Yates: choose `count` distinct integers from [0, n).
* Used for k-SemStamp valid-cluster selection (small n = K clusters).
*/
export function seededSample(seed: bigint, n: number, count: number): number[] {
const stream = new RandomStream(seed);
const arr = Array.from({ length: n }, (_, i) => i);
for (let i = n - 1; i > 0; i--) {
const j = Math.floor(stream.next() * (i + 1));
[arr[i], arr[j]] = [arr[j], arr[i]];
}
return arr.slice(0, count);
}
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