Implementations of SFC32/SFC64 chaotic RNGs

Cargo.toml

@@ -5,6 +5,7 @@ members = [
     "rand_xorshift",
     "rand_xoshiro",
     "rand_hc",
+    "rand_sfc"
 ]
 exclude = [
     "benches",

rand_sfc/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "rand_sfc"
+version = "0.1.0"
+edition = "2021"
+rust-version = "1.63"
+keywords = ["random", "rng", "sfc"]
+categories = ["algorithms", "no-std"]
+
+[features]
+serde1 = ["serde"]
+
+[dependencies]
+rand_core = { version = "0.9.0" }
+serde = { version = "1.0.118", default-features = false, features = ["derive"], optional = true }

rand_sfc/LICENSE-APACHE

@@ -0,0 +1,176 @@
+                              Apache License
+                        Version 2.0, January 2004
+                     https://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+   "License" shall mean the terms and conditions for use, reproduction,
+   and distribution as defined by Sections 1 through 9 of this document.
+
+   "Licensor" shall mean the copyright owner or entity authorized by
+   the copyright owner that is granting the License.
+
+   "Legal Entity" shall mean the union of the acting entity and all
+   other entities that control, are controlled by, or are under common
+   control with that entity. For the purposes of this definition,
+   "control" means (i) the power, direct or indirect, to cause the
+   direction or management of such entity, whether by contract or
+   otherwise, or (ii) ownership of fifty percent (50%) or more of the
+   outstanding shares, or (iii) beneficial ownership of such entity.
+
+   "You" (or "Your") shall mean an individual or Legal Entity
+   exercising permissions granted by this License.
+
+   "Source" form shall mean the preferred form for making modifications,
+   including but not limited to software source code, documentation
+   source, and configuration files.
+
+   "Object" form shall mean any form resulting from mechanical
+   transformation or translation of a Source form, including but
+   not limited to compiled object code, generated documentation,
+   and conversions to other media types.
+
+   "Work" shall mean the work of authorship, whether in Source or
+   Object form, made available under the License, as indicated by a
+   copyright notice that is included in or attached to the work
+   (an example is provided in the Appendix below).
+
+   "Derivative Works" shall mean any work, whether in Source or Object
+   form, that is based on (or derived from) the Work and for which the
+   editorial revisions, annotations, elaborations, or other modifications
+   represent, as a whole, an original work of authorship. For the purposes
+   of this License, Derivative Works shall not include works that remain
+   separable from, or merely link (or bind by name) to the interfaces of,
+   the Work and Derivative Works thereof.
+
+   "Contribution" shall mean any work of authorship, including
+   the original version of the Work and any modifications or additions
+   to that Work or Derivative Works thereof, that is intentionally
+   submitted to Licensor for inclusion in the Work by the copyright owner
+   or by an individual or Legal Entity authorized to submit on behalf of
+   the copyright owner. For the purposes of this definition, "submitted"
+   means any form of electronic, verbal, or written communication sent
+   to the Licensor or its representatives, including but not limited to
+   communication on electronic mailing lists, source code control systems,
+   and issue tracking systems that are managed by, or on behalf of, the
+   Licensor for the purpose of discussing and improving the Work, but
+   excluding communication that is conspicuously marked or otherwise
+   designated in writing by the copyright owner as "Not a Contribution."
+
+   "Contributor" shall mean Licensor and any individual or Legal Entity
+   on behalf of whom a Contribution has been received by Licensor and
+   subsequently incorporated within the Work.
+
+2. Grant of Copyright License. Subject to the terms and conditions of
+   this License, each Contributor hereby grants to You a perpetual,
+   worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+   copyright license to reproduce, prepare Derivative Works of,
+   publicly display, publicly perform, sublicense, and distribute the
+   Work and such Derivative Works in Source or Object form.
+
+3. Grant of Patent License. Subject to the terms and conditions of
+   this License, each Contributor hereby grants to You a perpetual,
+   worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+   (except as stated in this section) patent license to make, have made,
+   use, offer to sell, sell, import, and otherwise transfer the Work,
+   where such license applies only to those patent claims licensable
+   by such Contributor that are necessarily infringed by their
+   Contribution(s) alone or by combination of their Contribution(s)
+   with the Work to which such Contribution(s) was submitted. If You
+   institute patent litigation against any entity (including a
+   cross-claim or counterclaim in a lawsuit) alleging that the Work
+   or a Contribution incorporated within the Work constitutes direct
+   or contributory patent infringement, then any patent licenses
+   granted to You under this License for that Work shall terminate
+   as of the date such litigation is filed.
+
+4. Redistribution. You may reproduce and distribute copies of the
+   Work or Derivative Works thereof in any medium, with or without
+   modifications, and in Source or Object form, provided that You
+   meet the following conditions:
+
+   (a) You must give any other recipients of the Work or
+       Derivative Works a copy of this License; and
+
+   (b) You must cause any modified files to carry prominent notices
+       stating that You changed the files; and
+
+   (c) You must retain, in the Source form of any Derivative Works
+       that You distribute, all copyright, patent, trademark, and
+       attribution notices from the Source form of the Work,
+       excluding those notices that do not pertain to any part of
+       the Derivative Works; and
+
+   (d) If the Work includes a "NOTICE" text file as part of its
+       distribution, then any Derivative Works that You distribute must
+       include a readable copy of the attribution notices contained
+       within such NOTICE file, excluding those notices that do not
+       pertain to any part of the Derivative Works, in at least one
+       of the following places: within a NOTICE text file distributed
+       as part of the Derivative Works; within the Source form or
+       documentation, if provided along with the Derivative Works; or,
+       within a display generated by the Derivative Works, if and
+       wherever such third-party notices normally appear. The contents
+       of the NOTICE file are for informational purposes only and
+       do not modify the License. You may add Your own attribution
+       notices within Derivative Works that You distribute, alongside
+       or as an addendum to the NOTICE text from the Work, provided
+       that such additional attribution notices cannot be construed
+       as modifying the License.
+
+   You may add Your own copyright statement to Your modifications and
+   may provide additional or different license terms and conditions
+   for use, reproduction, or distribution of Your modifications, or
+   for any such Derivative Works as a whole, provided Your use,
+   reproduction, and distribution of the Work otherwise complies with
+   the conditions stated in this License.
+
+5. Submission of Contributions. Unless You explicitly state otherwise,
+   any Contribution intentionally submitted for inclusion in the Work
+   by You to the Licensor shall be under the terms and conditions of
+   this License, without any additional terms or conditions.
+   Notwithstanding the above, nothing herein shall supersede or modify
+   the terms of any separate license agreement you may have executed
+   with Licensor regarding such Contributions.
+
+6. Trademarks. This License does not grant permission to use the trade
+   names, trademarks, service marks, or product names of the Licensor,
+   except as required for reasonable and customary use in describing the
+   origin of the Work and reproducing the content of the NOTICE file.
+
+7. Disclaimer of Warranty. Unless required by applicable law or
+   agreed to in writing, Licensor provides the Work (and each
+   Contributor provides its Contributions) on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+   implied, including, without limitation, any warranties or conditions
+   of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+   PARTICULAR PURPOSE. You are solely responsible for determining the
+   appropriateness of using or redistributing the Work and assume any
+   risks associated with Your exercise of permissions under this License.
+
+8. Limitation of Liability. In no event and under no legal theory,
+   whether in tort (including negligence), contract, or otherwise,
+   unless required by applicable law (such as deliberate and grossly
+   negligent acts) or agreed to in writing, shall any Contributor be
+   liable to You for damages, including any direct, indirect, special,
+   incidental, or consequential damages of any character arising as a
+   result of this License or out of the use or inability to use the
+   Work (including but not limited to damages for loss of goodwill,
+   work stoppage, computer failure or malfunction, or any and all
+   other commercial damages or losses), even if such Contributor
+   has been advised of the possibility of such damages.
+
+9. Accepting Warranty or Additional Liability. While redistributing
+   the Work or Derivative Works thereof, You may choose to offer,
+   and charge a fee for, acceptance of support, warranty, indemnity,
+   or other liability obligations and/or rights consistent with this
+   License. However, in accepting such obligations, You may act only
+   on Your own behalf and on Your sole responsibility, not on behalf
+   of any other Contributor, and only if You agree to indemnify,
+   defend, and hold each Contributor harmless for any liability
+   incurred by, or claims asserted against, such Contributor by reason
+   of your accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS

rand_sfc/LICENSE-MIT

@@ -0,0 +1,25 @@
+Copyright 2025 Developers of the Rand project
+
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software
+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.

rand_sfc/src/lib.rs

@@ -0,0 +1,39 @@
+// Copyright 2025 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! This crate implements the sfc (Small Fast Counting) family of pseudorandom
+//! number generators designed by Chris Doty-Humphrey, author of the [PractRand]
+//! pseudorandom number generator testing suite. The generators have a small
+//! state, good statistical quality, and high performance. Like most generators
+//! intended for non-cryptographic use, they can be [predicted]. They also have
+//! a variable period, but the counter present in the state provides a fixed
+//! lower bound and [most states] are on the longest cycle.
+//!
+//! This crate provides:
+//! - [`Sfc64`]: 64 bit output, seed space 192 bits, worst-case period 2^64,
+//! and expected period ~2^255.
+//! - [`Sfc32`]: 32 bit output, seed space 96 bits, worst-case period 2^32,
+//! and expected period ~2^127.
+//!
+//! The implementations provided are derived from PractRand.
+//!
+//! [PractRand]: https://pracrand.sourceforge.net/
+//! [predicted]: https://github.com/michaelni/randomtests/blob/main/sfc64-breach.c
+//! [most states]: https://www.pcg-random.org/posts/random-invertible-mapping-statistics.html
+
+#![forbid(unsafe_code)]
+#![deny(missing_docs)]
+#![deny(missing_debug_implementations)]
+#![no_std]
+
+mod sfc32;
+mod sfc64;
+
+pub use rand_core;
+pub use sfc32::Sfc32;
+pub use sfc64::Sfc64;

rand_sfc/src/sfc32.rs

@@ -0,0 +1,124 @@
+// Copyright 2025 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use rand_core::le::read_u32_into;
+use rand_core::{RngCore, SeedableRng};
+use rand_core::impls::{fill_bytes_via_next, next_u64_via_u32};
+
+#[allow(missing_copy_implementations)]
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
+/// An sfc32 random number generator.
+///
+/// Good performance and statistical quality, but not cryptographically secure
+/// and has a large difference between its worst-case and maximum period.
+///
+/// This implementation is derived ultimately from
+/// [`the PractRand RNG test suite`](https://pracrand.sourceforge.net/) by
+/// Chris Doty-Humphrey.
+pub struct Sfc32 {
+    a: u32,
+    b: u32,
+    c: u32,
+    weyl: u32,
+}
+
+const BARREL_SHIFT: u32 = 21;
+const RSHIFT: u32 = 9;
+const LSHIFT: u32 = 3;
+// WEYL_INC is always 1 in the PractRand implementation, but some other
+// implementations use it to provide a stream facility. This is not yet
+// implemented here, though.
+const WEYL_INC: u32 = 1;
+
+impl RngCore for Sfc32 {
+    #[inline]
+    fn next_u32(&mut self) -> u32 {
+        let old_b = self.b;
+        let old_c = self.c;
+        let old_weyl = self.weyl;
+
+        let result = self.a.wrapping_add(old_b).wrapping_add(old_weyl);
+        self.a = old_b ^ (old_b >> RSHIFT);
+        self.b = old_c.wrapping_add(old_c << LSHIFT);
+        self.c = result.wrapping_add(old_c.rotate_left(BARREL_SHIFT));
+        self.weyl = old_weyl.wrapping_add(WEYL_INC);
+        result
+    }
+
+    #[inline]
+    fn next_u64(&mut self) -> u64 {
+        next_u64_via_u32(self)
+    }
+
+    #[inline]
+    fn fill_bytes(&mut self, dest: &mut [u8]) {
+        fill_bytes_via_next(self, dest);
+    }
+}
+
+// PracRand uses different mixing step counts for different types of seeds.
+// Here, just use one of the larger values always.
+const SEED_MIXING_STEPS: u32 = 16;
+
+impl SeedableRng for Sfc32 {
+    type Seed = [u8; 12];
+
+    /// Create a new `Sfc32`.
+    fn from_seed(seed: [u8; 12]) -> Sfc32 {
+        let mut s = [0; 3];
+        read_u32_into(&seed, &mut s);
+
+        let mut rng = Sfc32 {
+            a: s[0],
+            b: s[1],
+            c: s[2],
+            weyl: WEYL_INC
+        };
+
+        for _ in 0..SEED_MIXING_STEPS {
+            rng.next_u32();
+        }
+
+        rng
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn reference() {
+        // These values were produced with the reference implementation:
+        // https://pracrand.sourceforge.net/
+        let mut rng = Sfc32::from_seed([0, 0, 0, 0, 2, 0, 0, 0, 1, 0, 0, 0]);
+        let expected: [u32; 16] = [
+            0xA87DBC7E,
+            0x1787178C,
+            0x4C7B7234,
+            0xC65DADE2,
+            0x2C692349,
+            0xF52C2153,
+            0xDF098072,
+            0x9D49B03C,
+            0x9562381A,
+            0xC9B41738,
+            0x64B75E54,
+            0x36CE9B32,
+            0xF106947E,
+            0x0AFC726B,
+            0x549BBC87,
+            0xD19A7B3E
+        ];
+
+        for &e in &expected {
+            assert_eq!(rng.next_u32(), e);
+        }
+    }
+}