hare

commit 51543047bdb9dcf7a8206a5eeb0c1e0e3cae1fae
parent c66099085ccde84906ac368ee82214a7422bfd42
Author: Steven Guikal <void@fluix.dev>
Date:   Tue,  9 Mar 2021 03:41:05 -0500

math::random: new module

This package implements the SplitMix64 PRNG.

Diffstat:
A
math/random/random.ha
 | 
35
+++++++++++++++++++++++++++++++++++

1 file changed, 35 insertions(+), 0 deletions(-)
diff --git a/math/random/random.ha b/math/random/random.ha
@@ -0,0 +1,35 @@
+// math::random provides a pseudorandom number generator, which yields a
+// deterministic sequence of psuedo-random numbers based on a seed value.
+//
+// Beware! This module is NOT suitable for generating genuinely random data for
+// cryptographic use. See [crypto::random] for cryptographically secure random
+// number generation.
+
+// State for a pseudorandom number generator.
+export type random = u64;
+
+// Initializes a pseudorandom number generator with a given seed. This seed will
+// yield the same sequence of psuedo-random numbers if used again.
+export fn init(seed: u64) random = seed;
+
+// Returns a psuedo-random 64-bit unsigned integer.
+export fn next(r: *random) u64 = {
+	// SplitMix64
+	*r += 0x9e3779b97f4a7c15;
+	*r = (*r ^ *r >> 30) * 0xbf58476d1ce4e5b9;
+	*r = (*r ^ *r >> 27) * 0x94d049bb133111eb;
+	return *r ^ *r >> 31;
+};
+
+@test fn rng() void = {
+	let r = init(0);
+	let expected: [_]u64 = [
+		16294208416658607535,
+		15501543990041496116,
+		15737388954706874752,
+		15091258616627000950,
+	];
+	for (let i = 0z; i < len(expected); i += 1) {
+		assert(next(&r) == expected[i]);
+	};
+};