pcg-random/.scratch/stepBigInt.js

Implementation of the PCG random number generator for JavaScript

	var stepBigint = NO_BIGINTS ? noBigInts : (function() {
		var BI_U32_MAX = BigInt(0xffffffff);
		var BI_27 = BigInt(27);
		var BI_18 = BigInt(18);
		var BI_59 = BigInt(59);
		var BI_31 = BigInt(31);
		var BI_32 = BigInt(32);
		var BI_U64_MAX = ((BI_U32_MAX << BI_32) | BI_U32_MAX);
		var BI_MUL = (BigInt(MUL_HI) << BI_32) | BigInt(MUL_LO);

		function mix(oldState) {
			var xorshifted = (((oldState >> BI_18) ^ oldState) >> BI_27) & BI_U32_MAX;
			var rot = (oldState >> BI_59);
			var nrot = (-rot) & BI_31;
			var result = ((xorshifted >> rot) | (xorshifted << nrot)) & BI_U32_MAX;
			return result;
		}

		function finish(stateArr, newState, result) {
			stateArr[0] = Number(newState & BI_U32_MAX);
			stateArr[1] = Number((newState >> BI_32) & BI_U32_MAX);
			return Number(result) >>> 0;
		}

		function stepBigint(stateArr) {
			var oldState = (BigInt(stateArr[1]) << BI_32) | BigInt(stateArr[0]);
			var inc = (BigInt(stateArr[3]) << BI_32) | BigInt(stateArr[2]);
			var newState = ((oldState * BI_MUL) + inc) & BI_U64_MAX;
			var result = mix(oldState, inc);
			return finish(stateArr, newState, result);
		}
		return stepBigint;
	}());
	/**
	 * By default, if `BigInt` support is detected, we'll use them for certain
	 * operations in the internals.
	 *
	 * This is intended to be more efficient, but it may turn out that this
	 * causes performance problems for certain JavaScript implementations.
	 *
	 * If this is the case, you can set `PcgRandom.NO_BIGINTS = false`, and
	 * we'll never use them, even if they are available. I'd be interested to
	 * hear if you have this issue (I expect it might be possible though,
	 * because bigints generate garbage...).
	 *
	 * (Note that this only impacts whether we use bigints internally, and
	 * nothing about the API. The `setSeed` "overload" that accepts bigints will
	 * still work if you disable this).
	 *
	 * Note that while this defaults to `true` when bigints are supported, it is
	 * safe to set this to `true` even if they are not. We will only use bigints
	 * `if (PcgRandom.USE_BIGINTS && !NO_BIGINTS)`.
	 */
	PcgRandom.USE_BIGINTS = !NO_BIGINTS;