From f09cfccd8f77e0ca4af47ff556995514615a428a Mon Sep 17 00:00:00 2001
From: James Liu <contact@jamessliu.com>
Date: Sun, 14 Apr 2024 05:13:06 -0700
Subject: [PATCH] Optimized Clone::clone_from implementation (#127)

---
 src/block/mod.rs |  5 ++++-
 src/lib.rs       | 31 ++++++++++++++++++++++++++++---
 tests/tests.rs   | 27 +++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 4 deletions(-)

diff --git a/src/block/mod.rs b/src/block/mod.rs
index 05de0c8..ae7c222 100644
--- a/src/block/mod.rs
+++ b/src/block/mod.rs
@@ -1,5 +1,8 @@
 #![allow(clippy::undocumented_unsafe_blocks)]
 #![allow(dead_code)]
+// TODO: Remove once the transmutes are fixed
+#![allow(unknown_lints)]
+#![allow(clippy::missing_transmute_annotations)]
 
 use core::cmp::Ordering;
 use core::hash::{Hash, Hasher};
@@ -66,7 +69,7 @@ pub use self::wasm::*;
 impl Block {
     pub const USIZE_COUNT: usize = core::mem::size_of::<Self>() / core::mem::size_of::<usize>();
     pub const NONE: Self = Self::from_usize_array([0; Self::USIZE_COUNT]);
-    pub const ALL: Self = Self::from_usize_array([core::usize::MAX; Self::USIZE_COUNT]);
+    pub const ALL: Self = Self::from_usize_array([usize::MAX; Self::USIZE_COUNT]);
     pub const BITS: usize = core::mem::size_of::<Self>() * 8;
 
     #[inline]
diff --git a/src/lib.rs b/src/lib.rs
index 10a871c..313927a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -990,7 +990,7 @@ impl Hash for FixedBitSet {
 
 impl PartialEq for FixedBitSet {
     fn eq(&self, other: &Self) -> bool {
-        self.as_simd_slice().eq(other.as_simd_slice()) && self.length == other.length
+        self.length == other.length && self.as_simd_slice().eq(other.as_simd_slice())
     }
 }
 
@@ -1201,9 +1201,9 @@ impl Masks {
 
         Masks {
             first_block,
-            first_mask: usize::max_value() << first_rem,
+            first_mask: usize::MAX << first_rem,
             last_block,
-            last_mask: (usize::max_value() >> 1) >> (BITS - last_rem - 1),
+            last_mask: (usize::MAX >> 1) >> (BITS - last_rem - 1),
             // this is equivalent to `MAX >> (BITS - x)` with correct semantics when x == 0.
         }
     }
@@ -1406,6 +1406,31 @@ impl Clone for FixedBitSet {
     fn clone(&self) -> Self {
         Self::from_blocks_and_len(Vec::from(self.as_simd_slice()), self.length)
     }
+
+    #[inline]
+    fn clone_from(&mut self, source: &Self) {
+        {
+            let me = self.as_mut_simd_slice();
+            let them = source.as_simd_slice();
+            match me.len().cmp(&them.len()) {
+                Ordering::Greater => {
+                    let (head, tail) = me.split_at_mut(them.len());
+                    head.copy_from_slice(them);
+                    tail.fill(SimdBlock::NONE);
+                    self.length = source.length;
+                    return;
+                }
+                Ordering::Equal => {
+                    me.copy_from_slice(them);
+                    self.length = source.length;
+                    return;
+                }
+                // Self is smaller than the source, this requires allocation.
+                Ordering::Less => {}
+            }
+        }
+        *self = source.clone();
+    }
 }
 
 /// Return **true** if the bit is enabled in the bitset,
diff --git a/tests/tests.rs b/tests/tests.rs
index 385cf5d..fcc334d 100644
--- a/tests/tests.rs
+++ b/tests/tests.rs
@@ -1284,3 +1284,30 @@ fn test_is_full() {
     fb.insert_range(..);
     assert!(fb.is_full());
 }
+
+#[test]
+fn clone() {
+    let mut fb = FixedBitSet::with_capacity(10000);
+    fb.set(11, true);
+    fb.set(12, true);
+    fb.set(7, true);
+    fb.set(35, true);
+    fb.set(40, true);
+    fb.set(77, true);
+    fb.set(95, true);
+    fb.set(50, true);
+    fb.set(99, true);
+
+    let fb_clone = fb.clone();
+    let mut fb_clone_from_smaller = FixedBitSet::with_capacity(1000000);
+    let mut fb_clone_from_same = FixedBitSet::with_capacity(10000);
+    let mut fb_clone_from_bigger = FixedBitSet::with_capacity(100);
+    fb_clone_from_smaller.clone_from(&fb);
+    fb_clone_from_same.clone_from(&fb);
+    fb_clone_from_bigger.clone_from(&fb);
+
+    assert_eq!(&fb, &fb_clone);
+    assert_eq!(&fb, &fb_clone_from_smaller);
+    assert_eq!(&fb, &fb_clone_from_same);
+    assert_eq!(&fb, &fb_clone_from_bigger);
+}