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//! Xoshiro256++ - http://xoroshiro.di.unimi.it/
//!
//! PRNG
const std = @import("std");
const math = std.math;
const Xoshiro256 = @This();
s: [4]u64,
pub fn init(init_s: u64) Xoshiro256 {
var x = Xoshiro256{
.s = undefined,
};
x.seed(init_s);
return x;
}
pub fn random(self: *Xoshiro256) std.Random {
return std.Random.init(self, fill);
}
pub fn next(self: *Xoshiro256) u64 {
const r = math.rotl(u64, self.s[0] +% self.s[3], 23) +% self.s[0];
const t = self.s[1] << 17;
self.s[2] ^= self.s[0];
self.s[3] ^= self.s[1];
self.s[1] ^= self.s[2];
self.s[0] ^= self.s[3];
self.s[2] ^= t;
self.s[3] = math.rotl(u64, self.s[3], 45);
return r;
}
// Skip 2^128 places ahead in the sequence
pub fn jump(self: *Xoshiro256) void {
var s: u256 = 0;
var table: u256 = 0x39abdc4529b1661ca9582618e03fc9aad5a61266f0c9392c180ec6d33cfd0aba;
while (table != 0) : (table >>= 1) {
if (@as(u1, @truncate(table)) != 0) {
s ^= @as(u256, @bitCast(self.s));
}
_ = self.next();
}
self.s = @as([4]u64, @bitCast(s));
}
pub fn seed(self: *Xoshiro256, init_s: u64) void {
// Xoshiro requires 256-bits of seed.
var gen = std.Random.SplitMix64.init(init_s);
self.s[0] = gen.next();
self.s[1] = gen.next();
self.s[2] = gen.next();
self.s[3] = gen.next();
}
pub fn fill(self: *Xoshiro256, buf: []u8) void {
var i: usize = 0;
const aligned_len = buf.len - (buf.len & 7);
// Complete 8 byte segments.
while (i < aligned_len) : (i += 8) {
var n = self.next();
comptime var j: usize = 0;
inline while (j < 8) : (j += 1) {
buf[i + j] = @as(u8, @truncate(n));
n >>= 8;
}
}
// Remaining. (cuts the stream)
if (i != buf.len) {
var n = self.next();
while (i < buf.len) : (i += 1) {
buf[i] = @as(u8, @truncate(n));
n >>= 8;
}
}
}
test "sequence" {
if (@import("builtin").zig_backend == .stage2_c) return error.SkipZigTest;
var r = Xoshiro256.init(0);
const seq1 = [_]u64{
0x53175d61490b23df,
0x61da6f3dc380d507,
0x5c0fdf91ec9a7bfc,
0x02eebf8c3bbe5e1a,
0x7eca04ebaf4a5eea,
0x0543c37757f08d9a,
};
for (seq1) |s| {
try std.testing.expect(s == r.next());
}
r.jump();
const seq2 = [_]u64{
0xae1db5c5e27807be,
0xb584c6a7fd8709fe,
0xc46a0ee9330fb6e,
0xdc0c9606f49ed76e,
0x1f5bb6540f6651fb,
0x72fa2ca734601488,
};
for (seq2) |s| {
try std.testing.expect(s == r.next());
}
}
test fill {
var r = Xoshiro256.init(0);
const seq = [_]u64{
0x53175d61490b23df,
0x61da6f3dc380d507,
0x5c0fdf91ec9a7bfc,
0x02eebf8c3bbe5e1a,
0x7eca04ebaf4a5eea,
0x0543c37757f08d9a,
};
for (seq) |s| {
var buf0: [8]u8 = undefined;
var buf1: [7]u8 = undefined;
std.mem.writeInt(u64, &buf0, s, .little);
r.fill(&buf1);
try std.testing.expect(std.mem.eql(u8, buf0[0..7], buf1[0..]));
}
}
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