Added Xorshiro128++ random number generator. (#2846)

* Added Xorshiro128++ random number generator.

* Fixes to xorshiro implementation + tests.

---------

Co-authored-by: Christoffer Lerno <christoffer@aegik.com>

lib/std/math/random/math.xorshiro.c3

@@ -0,0 +1,42 @@
+module std::math::random;
+
+struct Xorshiro128PPRandom (Random)
+{
+	uint[4] state;
+}
+
+<*
+ @require seed.len > 0
+*>
+fn void Xorshiro128PPRandom.set_seed(&self, char[] seed) @dynamic
+{
+	self.state = random::make_seed(uint[4], seed);
+}
+
+// Xorshiro128++ implementation
+fn uint Xorshiro128PPRandom.next_int(&self) @dynamic
+{
+	uint result = (self.state[0] + self.state[3]).rotl(7) + self.state[0];
+
+	uint t  = self.state[1] << 9U;
+
+	self.state[2] ^= self.state[0];
+	self.state[3] ^= self.state[1];
+	self.state[1] ^= self.state[2];
+	self.state[0] ^= self.state[3];
+
+	self.state[2] ^= t;
+
+	self.state[3] = self.state[3].rotl(11);
+
+	return result;
+}
+
+<*
+ @require bytes.len > 0
+*>
+fn void Xorshiro128PPRandom.next_bytes(&self, char[] bytes) @dynamic => @random_value_to_bytes(self.next_int, bytes);
+fn uint128 Xorshiro128PPRandom.next_int128(&self) @dynamic => @long_to_int128(self.next_long());
+fn ulong Xorshiro128PPRandom.next_long(&self) @dynamic => @int_to_long(self.next_int());
+fn ushort Xorshiro128PPRandom.next_short(&self) @dynamic => (ushort)self.next_int();
+fn char Xorshiro128PPRandom.next_byte(&self) @dynamic => (char)self.next_int();

releasenotes.md

@@ -15,6 +15,7 @@
 - Added PEM encoding/decoding. #2858
 - Add Murmur3 hash.
 - Add optional line-length limitations to `io::readline` and `io::readline_to_stream`. #2879
+- Add Xorshiro128++.
 
 ### Fixes
 - Add error message if directory with output file name already exists

test/unit/stdlib/math/random_xorshiro.c3

@@ -0,0 +1,15 @@
+module xorshiro_test;
+import std::math;
+
+fn void test_vectors_xorshiro() @test
+{
+	Xorshiro128PPRandom a = { { 0x1, 0x2, 0x3, 0x4 } };
+	test::eq(0x281, a.next_int());
+	test::eq(0x180387, a.next_int());
+	test::eq(0xc0183387, a.next_int());
+
+	a = { { ~0x1, ~0x2, ~0x3, ~0x4 } };
+	test::eq(0xfffffcfd, a.next_int());
+	test::eq(0x17fbf8, a.next_int());
+	test::eq(0x40183386, a.next_int());
+}