Merge portable-simd#207 - ./feature/simplify-select

Remove Select trait

I realized that our `select` implementation predated `Simd` being generic over element type, and we don't really need the `Select` trait at all. The function signature is much simpler now (generic over element type, rather than over the entire vector). This did require changing mask select to be a different function, but I think that's fine considering they're not necessarily vectors.

Author: workingjubilee

crates/core_simd/src/mod.rs

@@ -27,7 +27,6 @@ pub mod simd {
 
     pub use crate::core_simd::lane_count::{LaneCount, SupportedLaneCount};
     pub use crate::core_simd::masks::*;
-    pub use crate::core_simd::select::Select;
     pub use crate::core_simd::swizzle::*;
     pub use crate::core_simd::vector::*;
 }

crates/core_simd/src/select.rs

@@ -1,54 +1,6 @@
 use crate::simd::intrinsics;
 use crate::simd::{LaneCount, Mask, MaskElement, Simd, SimdElement, SupportedLaneCount};
 
-mod sealed {
-    pub trait Sealed<Mask> {
-        fn select(mask: Mask, true_values: Self, false_values: Self) -> Self;
-    }
-}
-use sealed::Sealed;
-
-/// Supporting trait for vector `select` function
-pub trait Select<Mask>: Sealed<Mask> {}
-
-impl<T, const LANES: usize> Sealed<Mask<T::Mask, LANES>> for Simd<T, LANES>
-where
-    T: SimdElement,
-    LaneCount<LANES>: SupportedLaneCount,
-{
-    #[inline]
-    #[must_use = "method returns a new vector and does not mutate the original inputs"]
-    fn select(mask: Mask<T::Mask, LANES>, true_values: Self, false_values: Self) -> Self {
-        unsafe { intrinsics::simd_select(mask.to_int(), true_values, false_values) }
-    }
-}
-
-impl<T, const LANES: usize> Select<Mask<T::Mask, LANES>> for Simd<T, LANES>
-where
-    T: SimdElement,
-    LaneCount<LANES>: SupportedLaneCount,
-{
-}
-
-impl<T, const LANES: usize> Sealed<Self> for Mask<T, LANES>
-where
-    T: MaskElement,
-    LaneCount<LANES>: SupportedLaneCount,
-{
-    #[inline]
-    #[must_use = "method returns a new vector and does not mutate the original inputs"]
-    fn select(mask: Self, true_values: Self, false_values: Self) -> Self {
-        mask & true_values | !mask & false_values
-    }
-}
-
-impl<T, const LANES: usize> Select<Self> for Mask<T, LANES>
-where
-    T: MaskElement,
-    LaneCount<LANES>: SupportedLaneCount,
-{
-}
-
 impl<T, const LANES: usize> Mask<T, LANES>
 where
     T: MaskElement,
@@ -69,21 +21,37 @@ where
     /// let c = mask.select(a, b);
     /// assert_eq!(c.to_array(), [0, 5, 6, 3]);
     /// ```
+    #[inline]
+    #[must_use = "method returns a new vector and does not mutate the original inputs"]
+    pub fn select<U>(
+        self,
+        true_values: Simd<U, LANES>,
+        false_values: Simd<U, LANES>,
+    ) -> Simd<U, LANES>
+    where
+        U: SimdElement<Mask = T>,
+    {
+        unsafe { intrinsics::simd_select(self.to_int(), true_values, false_values) }
+    }
+
+    /// Choose lanes from two masks.
+    ///
+    /// For each lane in the mask, choose the corresponding lane from `true_values` if
+    /// that lane mask is true, and `false_values` if that lane mask is false.
     ///
-    /// `select` can also be used on masks:
     /// ```
     /// # #![feature(portable_simd)]
     /// # #[cfg(feature = "std")] use core_simd::Mask;
     /// # #[cfg(not(feature = "std"))] use core::simd::Mask;
     /// let a = Mask::<i32, 4>::from_array([true, true, false, false]);
     /// let b = Mask::<i32, 4>::from_array([false, false, true, true]);
     /// let mask = Mask::<i32, 4>::from_array([true, false, false, true]);
-    /// let c = mask.select(a, b);
+    /// let c = mask.select_mask(a, b);
     /// assert_eq!(c.to_array(), [true, false, true, false]);
     /// ```
     #[inline]
-    #[must_use = "method returns a new vector and does not mutate the original inputs"]
-    pub fn select<S: Select<Self>>(self, true_values: S, false_values: S) -> S {
-        S::select(self, true_values, false_values)
+    #[must_use = "method returns a new mask and does not mutate the original inputs"]
+    pub fn select_mask(self, true_values: Self, false_values: Self) -> Self {
+        self & true_values | !self & false_values
     }
 }