From 62138fd9a43a2d5ce6a90f31ab13a1ea0be8b2de Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Tue, 1 Aug 2023 23:27:47 +0200
Subject: [PATCH] First commit.  The hashes and their inverses.

---
 .gitignore |   2 ++
 Cargo.toml |   8 +++++
 src/lib.rs | 101 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 111 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.toml
 create mode 100644 src/lib.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..4fffb2f
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/target
+/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..a6c0ab3
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "bit_mixers"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..8526767
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,101 @@
+/// 32-bit bijective bit mixer.
+///
+/// https://github.com/skeeto/hash-prospector
+pub fn mix32(mut n: u32) -> u32 {
+    n ^= n >> 16;
+    n = n.wrapping_mul(0x21f0aaad);
+    n ^= n >> 15;
+    n = n.wrapping_mul(0xd35a2d97);
+    n ^= n >> 15;
+
+    n
+}
+
+/// Inverse of `mix32()`.
+pub fn mix32_inv(mut n: u32) -> u32 {
+    n ^= (n >> 15) ^ (n >> 30);
+    n = n.wrapping_mul(0x37132227);
+    n ^= (n >> 15) ^ (n >> 30);
+    n = n.wrapping_mul(0x333c4925);
+    n ^= n >> 16;
+
+    n
+}
+
+/// 64-bit bijective bit mixer.
+///
+/// http://zimbry.blogspot.ch/2011/09/better-bit-mixing-improving-on.html
+pub fn mix64(mut n: u64) -> u64 {
+    n ^= n >> 31;
+    n = n.wrapping_mul(0x7fb5d329728ea185);
+    n ^= n >> 27;
+    n = n.wrapping_mul(0x81dadef4bc2dd44d);
+    n ^= n >> 33;
+
+    n
+}
+
+/// Inverse of `mix64()`.
+pub fn mix64_inv(mut n: u64) -> u64 {
+    n ^= n >> 33;
+    n = n.wrapping_mul(0x4d6dff26c61d8485);
+    n ^= (n >> 27) ^ (n >> 54);
+    n = n.wrapping_mul(0x4c5ff4596f4a2f4d);
+    n ^= (n >> 31) ^ (n >> 62);
+
+    n
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // fn compute_multiplicative_inverse_32(a: u32) -> u32 {
+    //     assert!(a & 1 == 1);
+    //     let mut x = a;
+    //     // Overkill iteration count.
+    //     for _ in 0..100 {
+    //         // x += x - a * x * x;
+    //         x = x.wrapping_add(x.wrapping_sub(a.wrapping_mul(x).wrapping_mul(x)));
+    //     }
+
+    //     x
+    // }
+
+    // fn compute_multiplicative_inverse_64(a: u64) -> u64 {
+    //     assert!(a & 1 == 1);
+    //     let mut x = a;
+    //     // Overkill iteration count.
+    //     for _ in 0..100 {
+    //         // x += x - a * x * x;
+    //         x = x.wrapping_add(x.wrapping_sub(a.wrapping_mul(x).wrapping_mul(x)));
+    //     }
+
+    //     x
+    // }
+
+    // #[test]
+    // fn get_inverse() {
+    //     // Panic, to print the result.
+    //     panic!("0x{:x}", compute_multiplicative_inverse_32(0x21f0aaad));
+    //     panic!("0x{:x}", compute_multiplicative_inverse_32(0xd35a2d97));
+    // }
+
+    #[test]
+    fn mix32_invertability() {
+        for i in 0..9999999u32 {
+            let n = mix32(mix32(mix32(i)));
+            assert_eq!(n, mix32_inv(mix32(n)));
+            assert_eq!(n, mix32(mix32_inv(n)));
+        }
+    }
+
+    #[test]
+    fn mix64_invertability() {
+        for i in 0..9999999u64 {
+            let n = mix64(mix64(mix64(i)));
+            assert_eq!(n, mix64_inv(mix64(n)));
+            assert_eq!(n, mix64(mix64_inv(n)));
+        }
+    }
+}