diff --git a/lib/std/rand.zig b/lib/std/rand.zig index 980722cdff..72537e952f 100644 --- a/lib/std/rand.zig +++ b/lib/std/rand.zig @@ -26,6 +26,7 @@ pub const Pcg = @import("rand/Pcg.zig"); pub const Xoroshiro128 = @import("rand/Xoroshiro128.zig"); pub const Xoshiro256 = @import("rand/Xoshiro256.zig"); pub const Sfc64 = @import("rand/Sfc64.zig"); +pub const RomuTrio = @import("rand/RomuTrio.zig"); pub const Random = struct { ptr: *anyopaque, diff --git a/lib/std/rand/RomuTrio.zig b/lib/std/rand/RomuTrio.zig new file mode 100644 index 0000000000..ff7b4deac1 --- /dev/null +++ b/lib/std/rand/RomuTrio.zig @@ -0,0 +1,132 @@ +// Website: romu-random.org +// Reference paper: http://arxiv.org/abs/2002.11331 +// Beware: this PRNG is trivially predictable. While fast, it should *never* be used for cryptographic purposes. + +const std = @import("std"); +const Random = std.rand.Random; +const math = std.math; +const RomuTrio = @This(); + +x_state: u64, +y_state: u64, +z_state: u64, // set to nonzero seed + +pub fn init(init_s: u64) RomuTrio { + var x = RomuTrio{ .x_state = undefined, .y_state = undefined, .z_state = undefined }; + x.seed(init_s); + return x; +} + +pub fn random(self: *RomuTrio) Random { + return Random.init(self, fill); +} + +fn next(self: *RomuTrio) u64 { + const xp = self.x_state; + const yp = self.y_state; + const zp = self.z_state; + self.x_state = 15241094284759029579 *% zp; + self.y_state = yp -% xp; + self.y_state = std.math.rotl(u64, self.y_state, 12); + self.z_state = zp -% yp; + self.z_state = std.math.rotl(u64, self.z_state, 44); + return xp; +} + +pub fn seedWithBuf(self: *RomuTrio, buf: [24]u8) void { + const seed_buf = @bitCast([3]u64, buf); + self.x_state = seed_buf[0]; + self.y_state = seed_buf[1]; + self.z_state = seed_buf[2]; +} + +pub fn seed(self: *RomuTrio, init_s: u64) void { + // RomuTrio requires 192-bits of seed. + var gen = std.rand.SplitMix64.init(init_s); + + self.x_state = gen.next(); + self.y_state = gen.next(); + self.z_state = gen.next(); +} + +pub fn fill(self: *RomuTrio, 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] = @truncate(u8, n); + n >>= 8; + } + } + + // Remaining. (cuts the stream) + if (i != buf.len) { + var n = self.next(); + while (i < buf.len) : (i += 1) { + buf[i] = @truncate(u8, n); + n >>= 8; + } + } +} + +test "RomuTrio sequence" { + // Unfortunately there does not seem to be an official test sequence. + var r = RomuTrio.init(0); + + const seq = [_]u64{ + 16294208416658607535, + 13964609475759908645, + 4703697494102998476, + 3425221541186733346, + 2285772463536419399, + 9454187757529463048, + 13695907680080547496, + 8328236714879408626, + 12323357569716880909, + 12375466223337721820, + }; + + for (seq) |s| { + try std.testing.expectEqual(s, r.next()); + } +} + +test "RomuTrio fill" { + // Unfortunately there does not seem to be an official test sequence. + var r = RomuTrio.init(0); + + const seq = [_]u64{ + 16294208416658607535, + 13964609475759908645, + 4703697494102998476, + 3425221541186733346, + 2285772463536419399, + 9454187757529463048, + 13695907680080547496, + 8328236714879408626, + 12323357569716880909, + 12375466223337721820, + }; + + for (seq) |s| { + var buf0: [8]u8 = undefined; + var buf1: [7]u8 = undefined; + std.mem.writeIntLittle(u64, &buf0, s); + r.fill(&buf1); + try std.testing.expect(std.mem.eql(u8, buf0[0..7], buf1[0..])); + } +} + +test "RomuTrio buf seeding test" { + const buf0 = @bitCast([24]u8, [3]u64{ 16294208416658607535, 13964609475759908645, 4703697494102998476 }); + const resulting_state = .{ .x = 16294208416658607535, .y = 13964609475759908645, .z = 4703697494102998476 }; + var r = RomuTrio.init(0); + r.seedWithBuf(buf0); + try std.testing.expect(r.x_state == resulting_state.x); + try std.testing.expect(r.y_state == resulting_state.y); + try std.testing.expect(r.z_state == resulting_state.z); +}