From 9ed3c51362958356639ecd9a8a0a4cb88a018b37 Mon Sep 17 00:00:00 2001
From: Caleb Zulawski <caleb.zulawski@gmail.com>
Date: Mon, 6 Jun 2022 11:25:22 -0400
Subject: [PATCH] Add splat_lane

---
 crates/core_simd/src/swizzle.rs   | 15 +++++++++++++++
 crates/core_simd/tests/swizzle.rs | 10 ++++++++++
 2 files changed, 25 insertions(+)

diff --git a/crates/core_simd/src/swizzle.rs b/crates/core_simd/src/swizzle.rs
index 22999d24950..7a8b52dd3cf 100644
--- a/crates/core_simd/src/swizzle.rs
+++ b/crates/core_simd/src/swizzle.rs
@@ -188,6 +188,21 @@ where
     T: SimdElement,
     LaneCount<LANES>: SupportedLaneCount,
 {
+    /// Splat a lane to the other lanes in the vector.
+    ///
+    /// Equivalent to `Simd::splat(self[LANE])`, but may be faster.
+    #[inline]
+    #[must_use = "method returns a new vector and does not mutate the original inputs"]
+    pub fn splat_lane<const LANE: usize>(self) -> Self {
+        struct Splat<const LANE: usize>;
+
+        impl<const LANE: usize, const LANES: usize> Swizzle<LANES, LANES> for Splat<LANE> {
+            const INDEX: [usize; LANES] = [LANE; LANES];
+        }
+
+        Splat::<LANE>::swizzle(self)
+    }
+
     /// Reverse the order of the lanes in the vector.
     #[inline]
     #[must_use = "method returns a new vector and does not mutate the original inputs"]
diff --git a/crates/core_simd/tests/swizzle.rs b/crates/core_simd/tests/swizzle.rs
index 51c63611aba..638aea539ff 100644
--- a/crates/core_simd/tests/swizzle.rs
+++ b/crates/core_simd/tests/swizzle.rs
@@ -23,6 +23,16 @@ fn swizzle() {
     assert_eq!(Index::swizzle(vector).to_array(), [4, 4]);
 }
 
+#[test]
+#[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+fn splat_lane() {
+    let a = Simd::from_array([1, 2, 3, 4]);
+    assert_eq!(a.splat_lane::<0>().to_array(), [1; 4]);
+    assert_eq!(a.splat_lane::<1>().to_array(), [2; 4]);
+    assert_eq!(a.splat_lane::<2>().to_array(), [3; 4]);
+    assert_eq!(a.splat_lane::<3>().to_array(), [4; 4]);
+}
+
 #[test]
 #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
 fn reverse() {