apps/cf-ai-backend/src/utils/seededRandom.ts


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import { MersenneTwister19937, integer } from "random-js";

/**
 * Hashes a string to a 32-bit integer.
 * @param {string} seed - The input string to hash.
 */
function hashString(seed: string) {
  let hash = 0;
  for (let i = 0; i < seed.length; i++) {
    const char = seed.charCodeAt(i);
    hash = (hash << 5) - hash + char;
    hash |= 0; // Convert to 32bit integer
  }
  return hash;
}

/**
 * returns a funtion that generates same sequence of random numbers for a given seed between 0 and 1.
 */
export function seededRandom(seed: string) {
  const seedHash = hashString(seed);
  const engine = MersenneTwister19937.seed(seedHash);
  return () =>
    integer(0, Number.MAX_SAFE_INTEGER)(engine) / Number.MAX_SAFE_INTEGER;
}