tests/rand.mjs: Add MersenneTwister random number generator

The `tests/rand.c` is also added: a simplified adaptation of the
original algorithm implementation in C.  A 10k numbers test case shows
that the JavaScript version behaves the same that the C one does.

3 files changed, 234 insertions, 0 deletions

diff --git a/tests/js/rand.mjs b/tests/js/rand.mjs
new file mode 100644
index 0000000..4044bb8
--- /dev/null
+++ b/tests/js/rand.mjs
@@ -0,0 +1,96 @@
+import assert from "node:assert/strict";
+import fs     from "node:fs";
+
+import * as runner from "../runner.mjs";
+import {
+	makeRandom,
+} from "../rand.mjs";
+
+
+const test_makeRandom = async t => {
+	t.start("makeRandom()");
+
+	await t.test("known expected values", () => {
+		const expected1 = [
+			545331265,  2211535594, 4152021490, 3857419313,
+			1118735928, 3031474347, 3853601519, 3345048107,
+			1618127707, 4001288224, 1444061399, 2700534436,
+			1938647176, 1459718602, 3608868106, 926825740,
+			528719691,  508226068,  2332279787, 357437743,
+			1602075314, 1655472598, 1924131686, 4125580919,
+			555943458,  4047836046, 3693150918, 1515015978,
+			3523541186, 753964207,  1512058436, 682070622,
+			983063469,  4097791860, 3336260823, 603291380,
+			2554576084, 139062484,  590788013,  3608810491,
+			3663176645, 3481732081, 1011496919, 2935401636,
+			628041163,  3997974947, 2533467101, 2287863463,
+			2465361808, 1196937660, 263152482,  618228754,
+			2535860367, 3089904367, 1053769440, 1270818139,
+			1462199892, 49766906,   4229377745, 445624458,
+			3949395950, 4102223196, 162228180,  352248782,
+			3700326028, 965464548,  3236553557, 1342363444,
+			1740229486, 4006226087, 1475432391, 2100043423,
+			734083679,  2197742340, 1695047538, 2684537025,
+			2755935210, 2185177924, 1179365521, 682202996,
+			1985796754, 1203188028, 3742512741, 2573038834,
+			1722845493, 971634808,  2622456659, 1542773708,
+			506664990,  516191900,  3015858858, 2439287065,
+			1778261054, 3352336947, 1470361474, 2832338531,
+			2559479753, 2841821596, 858410480,  1311022275,
+		];
+
+		const expected2 = [
+			1867215825, 1512725508, 59490082,   898255083,
+			2128587452, 3375572255, 3011978101, 664390052,
+			712189293,  1309145867, 1574443536, 3005563625,
+			1937221174, 2592810353, 1221596501, 3864084723,
+			2447880554, 1373397507, 4101388729, 1434258649,
+			2876658371, 694177935,  1850641240, 2934786942,
+			3613830458, 3660625740, 1450431957, 978896710,
+			108365537,  1669305275, 1505684879, 1989942961,
+			4089952722, 2832268551, 27863256,   3866494241,
+			3916427650, 3309597508, 24597008,   3442418170,
+			1617059167, 175885832,  854293503,  3965431971,
+			3276364445, 4079612430, 1622146979, 1665096344,
+			2283667308, 2042586700, 2997013224, 1214521941,
+			860865914,  3204144669, 3352312876, 407025370,
+			1854088521, 1518454983, 2467488963, 3014922727,
+			667505194,  1382726996, 3519130642, 3473985175,
+			387425140,  826920070,  3222196824, 3272392876,
+			2814202151, 1958017767, 2343175108, 513394477,
+			983853656,  3389045986, 177790781,  1853562919,
+			1417029053, 115479138,  3505632337, 339954849,
+			2552460743, 1260703764, 1719642924, 3129628830,
+			1828716278, 3537151540, 4169628597, 444526909,
+			4191927207, 3891278677, 1954375449, 3973495864,
+			2231816005, 4062939046, 2084239497, 3470238230,
+			1145760705, 2114090486, 4245867725, 1687967890,
+		];
+
+		const expected3 = JSON.parse(
+			fs.readFileSync("tests/bigger-rand-output.txt"),
+		);
+
+		const given1 = Array.from(
+			new Array(expected1.length),
+			makeRandom(123456),
+		);
+		const given2 = Array.from(
+			new Array(expected2.length),
+			makeRandom(123457),
+		);
+		const given3 = Array.from(
+			new Array(expected3.length),
+			makeRandom(2222),
+		);
+
+		assert.deepEqual(given1, expected1);
+		assert.deepEqual(given2, expected2);
+		assert.deepEqual(given3, expected3);
+	});
+};
+
+
+await runner.runTests([
+	test_makeRandom,
+]);
diff --git a/tests/rand.c b/tests/rand.c
new file mode 100644
index 0000000..925d1ba
--- /dev/null
+++ b/tests/rand.c
@@ -0,0 +1,83 @@
+// Taken from
+// http://www.math.sci.hiroshima-u.ac.jp/m-mat/MT/MT2002/CODES/mt19937ar.c
+
+#define _XOPEN_SOURCE 700
+
+#include <assert.h>
+#include <inttypes.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+
+#define N 624U
+static const uint16_t M = 397;
+static const uint32_t MATRIX_A   = 0x9908b0dfUL;
+static const uint32_t UPPER_MASK = 0x80000000UL;
+static const uint32_t LOWER_MASK = 0x7fffffffUL;
+
+static uint32_t mt[N];
+static uint16_t mti;
+static bool initialized = false;
+
+static void
+init(uint32_t s) {
+	initialized = true;
+	mt[0] = s & 0xffffffffUL;
+	for (mti = 1; mti < N; mti++) {
+		mt[mti] = (1812433253 * (mt[mti - 1] ^ (mt[mti - 1] >> 30))) + mti;
+	}
+}
+
+/// Generates a random number on the [ 0, 0xffffffff ]-interval.
+static uint32_t
+generate(void) {
+	assert(initialized == true);
+	static uint32_t mag01[2] = { 0, MATRIX_A };
+
+	if (mti >= N) {
+		uint16_t kk;
+
+		for (kk = 0; kk < N - M; kk++) {
+			const uint32_t y0 =
+				(mt[kk]     & UPPER_MASK) |
+				(mt[kk + 1] & LOWER_MASK);
+			mt[kk] = mt[kk + M] ^ (y0 >> 1) ^ mag01[y0 & 1U];
+		}
+
+		for (; kk < N - 1; kk++) {
+			const uint32_t y1 =
+				(mt[kk]     & UPPER_MASK) |
+				(mt[kk + 1] & LOWER_MASK);
+			mt[kk] = mt[kk + (M - N)] ^ (y1 >> 1) ^ mag01[y1 & 1U];
+		}
+
+		const uint32_t y2 =
+			(mt[N - 1] & UPPER_MASK) |
+			(mt[0]     & LOWER_MASK);
+		mt[N - 1] = mt[M - 1] ^ (y2 >> 1) ^ mag01[y2 & 1U];
+		mti = 0;
+	}
+
+	uint32_t y = mt[mti++];
+
+	y ^= (y >> 11);
+	y ^= (y << 7)  & 0x9d2c5680UL;
+	y ^= (y << 15) & 0xefc60000UL;
+	y ^= (y >> 18);
+
+	return y;
+}
+
+
+int
+main(void) {
+	init(2222);
+
+	for (uint16_t i = 0; i < 10000; i++) {
+		assert(
+			printf("%" PRIu32 "\n", generate()) > 0
+		);
+	}
+
+	return 0;
+}
diff --git a/tests/rand.mjs b/tests/rand.mjs
new file mode 100644
index 0000000..ba4e3b1
--- /dev/null
+++ b/tests/rand.mjs
@@ -0,0 +1,55 @@
+const N          = 624;
+const M          = 397;
+const MATRIX_A   = 0x9908b0df;
+const UPPER_MASK = 0x80000000;
+const LOWER_MASK = 0x7fffffff;
+const mag01      = [ 0x0, MATRIX_A ];
+const INIT_MUL   = 1812433253;
+
+/// The given function generates random numbers on the [ 0, 0xffffffff ]-interval.
+export const makeRandom = (seed = (new Date()).getTime()) => {
+	const mt = new Array(N);
+	let mti  = null;
+
+	mt[0] = seed >>> 0;
+	for (mti = 1; mti < N; mti++) {
+		const s0 = mt[mti - 1] ^ (mt[mti - 1] >>> 30);
+		mt[mti] =
+			(((((s0 & 0xffff0000) >>> 16) * INIT_MUL) << 16) +
+			((   s0 & 0x0000ffff) * INIT_MUL) +
+			mti) >>> 0;
+	}
+
+	return () => {
+		if (mti >= N) {
+			let kk = null;
+
+			for (kk = 0; kk < N - M; kk++) {
+				const y0 =
+					(mt[kk]     & UPPER_MASK) |
+					(mt[kk + 1] & LOWER_MASK);
+				mt[kk] = mt[kk + M] ^ (y0 >>> 1) ^ mag01[y0 & 0x1];
+			}
+
+			for (; kk < N - 1; kk++) {
+				const y1 =
+					(mt[kk]     & UPPER_MASK) |
+					(mt[kk + 1] & LOWER_MASK);
+				mt[kk] = mt[kk + (M - N)] ^ (y1 >>> 1) ^ mag01[y1 & 0x1];
+			}
+
+			const y2 =
+				(mt[N - 1] & UPPER_MASK) |
+				(mt[0]     & LOWER_MASK);
+			mt[N - 1] = mt[M - 1] ^ (y2 >>> 1) ^ mag01[y2 & 0x1];
+			mti = 0;
+		}
+
+		let y = mt[mti++];
+		y ^= (y >>> 11);
+		y ^= (y <<  7)  & 0x9d2c5680;
+		y ^= (y <<  15) & 0xefc60000;
+		y ^= (y >>> 18);
+		return y >>> 0;
+	};
+};