cityhash32 final helper

SymmetricChaos · Oct 28, 2024 · e81df91 · e81df91
1 parent 43e2c7a
commit e81df91
Showing 1 changed file with 105 additions and 9 deletions.
diff --git a/hashers/src/cityhash.rs b/hashers/src/cityhash.rs
@@ -14,7 +14,7 @@ const C2: u32 = 0xe6546b64;
 const C3: u32 = 0x85ebca6b;
 const C4: u32 = 0xc2b2ae35;
 
-// Functions taken from Murmur3
+// Function taken from Murmur3
 fn final_mix(mut x: u32) -> u32 {
     x ^= x >> 16;
     x = x.wrapping_mul(C3);
@@ -33,13 +33,6 @@ fn compress(mut x: u32, mut y: u32) -> u32 {
     y.wrapping_mul(5).wrapping_add(C2)
 }
 
-macro_rules! permute3 {
-    ($a: ident, $b: ident, $c: ident) => {
-        std::mem::swap(&mut $a, &mut $b);
-        std::mem::swap(&mut $a, &mut $c);
-    };
-}
-
 fn fetch_u32(bytes: &[u8], p: usize) -> u32 {
     u32::from_le_bytes(bytes[p..p + 4].try_into().unwrap())
 }
@@ -83,7 +76,110 @@ fn hash32_13_to_24(bytes: &[u8]) -> u32 {
 }
 
 fn hash32_25(bytes: &[u8]) -> u32 {
-    todo!()
+    let l = bytes.len();
+    let mut h = l as u32;
+    let mut g = C0.wrapping_mul(h);
+    let mut f = g;
+    let a0 = fetch_u32(bytes, l - 4)
+        .wrapping_mul(C0)
+        .rotate_left(17)
+        .wrapping_mul(C1);
+    let a1 = fetch_u32(bytes, l - 8)
+        .wrapping_mul(C0)
+        .rotate_left(17)
+        .wrapping_mul(C1);
+    let a2 = fetch_u32(bytes, l - 16)
+        .wrapping_mul(C0)
+        .rotate_left(17)
+        .wrapping_mul(C1);
+    let a3 = fetch_u32(bytes, l - 12)
+        .wrapping_mul(C0)
+        .rotate_left(17)
+        .wrapping_mul(C1);
+    let a4 = fetch_u32(bytes, l - 20)
+        .wrapping_mul(C0)
+        .rotate_left(17)
+        .wrapping_mul(C1);
+    h ^= a0;
+    h = h.rotate_left(19).wrapping_mul(5).wrapping_add(C2);
+    h ^= a2;
+    h = h.rotate_left(19).wrapping_mul(5).wrapping_add(C2);
+    g ^= a1;
+    g = g.rotate_left(19).wrapping_mul(5).wrapping_add(C2);
+    g ^= a3;
+    g = g.rotate_left(19).wrapping_mul(5).wrapping_add(C2);
+    f ^= a4;
+    f = f.rotate_left(19).wrapping_mul(5).wrapping_add(C2);
+
+    let mut offset = 0;
+
+    for _ in 0..((l - 1) / 20) {
+        let a0 = fetch_u32(bytes, offset)
+            .wrapping_mul(C0)
+            .rotate_left(17)
+            .wrapping_mul(C1);
+        let a1 = fetch_u32(bytes, offset + 4);
+        let a2 = fetch_u32(bytes, 8)
+            .wrapping_mul(C0)
+            .rotate_left(17)
+            .wrapping_mul(C1);
+        let a3 = fetch_u32(bytes, offset + 12)
+            .wrapping_mul(C0)
+            .rotate_left(17)
+            .wrapping_mul(C1);
+        let a4 = fetch_u32(bytes, offset + 16);
+
+        h ^= a0;
+        h = h.rotate_left(18).wrapping_mul(5).wrapping_add(C2);
+
+        f = f.wrapping_add(a1).rotate_left(19).wrapping_mul(C0);
+
+        g = g
+            .wrapping_add(a2)
+            .rotate_left(18)
+            .wrapping_mul(5)
+            .wrapping_add(C2);
+
+        h ^= a3.wrapping_add(a1);
+        h = h.rotate_left(19).wrapping_mul(5).wrapping_add(C2);
+
+        g ^= a4;
+        g = g.swap_bytes().wrapping_mul(5);
+
+        h = h.wrapping_add(a4.wrapping_mul(5));
+        h = h.swap_bytes();
+
+        f = f.wrapping_add(a0);
+
+        std::mem::swap(&mut f, &mut h);
+        std::mem::swap(&mut f, &mut g);
+
+        offset += 20
+    }
+
+    g = g
+        .rotate_left(11)
+        .wrapping_mul(C0)
+        .rotate_left(17)
+        .wrapping_mul(C0);
+    f = f
+        .rotate_left(11)
+        .wrapping_mul(C0)
+        .rotate_left(17)
+        .wrapping_mul(C0);
+
+    h.wrapping_add(g)
+        .rotate_left(19)
+        .wrapping_mul(5)
+        .wrapping_add(C2)
+        .rotate_left(17)
+        .wrapping_mul(C0)
+        .wrapping_add(f)
+        .rotate_left(19)
+        .wrapping_mul(5)
+        .wrapping_add(C2)
+        .rotate_left(17)
+        .wrapping_mul(C0)
 }
 
 pub struct CityHash32 {