Merge pull request rust-lang#441 from sammysheep/shift_elements

shift_elements_{left,right}

Author: calebzulawski

crates/core_simd/src/swizzle.rs

@@ -251,6 +251,50 @@ where
         Rotate::<OFFSET>::swizzle(self)
     }
 
+    /// Shifts the vector elements to the left by `OFFSET`, filling in with
+    /// `padding` from the right.
+    #[inline]
+    #[must_use = "method returns a new vector and does not mutate the original inputs"]
+    pub fn shift_elements_left<const OFFSET: usize>(self, padding: T) -> Self {
+        struct Shift<const OFFSET: usize>;
+
+        impl<const OFFSET: usize, const N: usize> Swizzle<N> for Shift<OFFSET> {
+            const INDEX: [usize; N] = const {
+                let mut index = [N; N];
+                let mut i = 0;
+                while i + OFFSET < N {
+                    index[i] = i + OFFSET;
+                    i += 1;
+                }
+                index
+            };
+        }
+
+        Shift::<OFFSET>::concat_swizzle(self, Simd::splat(padding))
+    }
+
+    /// Shifts the vector elements to the right by `OFFSET`, filling in with
+    /// `padding` from the left.
+    #[inline]
+    #[must_use = "method returns a new vector and does not mutate the original inputs"]
+    pub fn shift_elements_right<const OFFSET: usize>(self, padding: T) -> Self {
+        struct Shift<const OFFSET: usize>;
+
+        impl<const OFFSET: usize, const N: usize> Swizzle<N> for Shift<OFFSET> {
+            const INDEX: [usize; N] = const {
+                let mut index = [N; N];
+                let mut i = OFFSET;
+                while i < N {
+                    index[i] = i - OFFSET;
+                    i += 1;
+                }
+                index
+            };
+        }
+
+        Shift::<OFFSET>::concat_swizzle(self, Simd::splat(padding))
+    }
+
     /// Interleave two vectors.
     ///
     /// The resulting vectors contain elements taken alternatively from `self` and `other`, first
@@ -451,6 +495,36 @@ where
         unsafe { Self::from_int_unchecked(self.to_int().rotate_elements_right::<OFFSET>()) }
     }
 
+    /// Shifts the mask elements to the left by `OFFSET`, filling in with
+    /// `padding` from the right.
+    #[inline]
+    #[must_use = "method returns a new mask and does not mutate the original inputs"]
+    pub fn shift_elements_left<const OFFSET: usize>(self, padding: bool) -> Self {
+        // Safety: swizzles are safe for masks
+        unsafe {
+            Self::from_int_unchecked(self.to_int().shift_elements_left::<OFFSET>(if padding {
+                T::TRUE
+            } else {
+                T::FALSE
+            }))
+        }
+    }
+
+    /// Shifts the mask elements to the right by `OFFSET`, filling in with
+    /// `padding` from the left.
+    #[inline]
+    #[must_use = "method returns a new mask and does not mutate the original inputs"]
+    pub fn shift_elements_right<const OFFSET: usize>(self, padding: bool) -> Self {
+        // Safety: swizzles are safe for masks
+        unsafe {
+            Self::from_int_unchecked(self.to_int().shift_elements_right::<OFFSET>(if padding {
+                T::TRUE
+            } else {
+                T::FALSE
+            }))
+        }
+    }
+
     /// Interleave two masks.
     ///
     /// The resulting masks contain elements taken alternatively from `self` and `other`, first

crates/core_simd/tests/swizzle.rs

@@ -48,6 +48,24 @@ fn rotate() {
     assert_eq!(a.rotate_elements_right::<5>().to_array(), [4, 1, 2, 3]);
 }
 
+#[test]
+#[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+fn shift() {
+    let a = Simd::from_array([1, 2, 3, 4]);
+    assert_eq!(a.shift_elements_left::<0>(0).to_array(), [1, 2, 3, 4]);
+    assert_eq!(a.shift_elements_left::<1>(0).to_array(), [2, 3, 4, 0]);
+    assert_eq!(a.shift_elements_left::<2>(9).to_array(), [3, 4, 9, 9]);
+    assert_eq!(a.shift_elements_left::<3>(8).to_array(), [4, 8, 8, 8]);
+    assert_eq!(a.shift_elements_left::<4>(7).to_array(), [7, 7, 7, 7]);
+    assert_eq!(a.shift_elements_left::<5>(6).to_array(), [6, 6, 6, 6]);
+    assert_eq!(a.shift_elements_right::<0>(0).to_array(), [1, 2, 3, 4]);
+    assert_eq!(a.shift_elements_right::<1>(0).to_array(), [0, 1, 2, 3]);
+    assert_eq!(a.shift_elements_right::<2>(-1).to_array(), [-1, -1, 1, 2]);
+    assert_eq!(a.shift_elements_right::<3>(-2).to_array(), [-2, -2, -2, 1]);
+    assert_eq!(a.shift_elements_right::<4>(-3).to_array(), [-3, -3, -3, -3]);
+    assert_eq!(a.shift_elements_right::<5>(-4).to_array(), [-4, -4, -4, -4]);
+}
+
 #[test]
 #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
 fn interleave() {