Add abs_diff function to SimdInt and SimdUint traits

Implement `abs_diff` for signed and unsigned integer vectors
Add tests for testing all `i8`s and `u8`s against the scalar `abs_diff`

crates/core_simd/src/simd/num/int.rs

@@ -1,6 +1,6 @@
 use super::sealed::Sealed;
 use crate::simd::{
-    cmp::SimdPartialOrd, num::SimdUint, LaneCount, Mask, Simd, SimdCast, SimdElement,
+    cmp::SimdOrd, cmp::SimdPartialOrd, num::SimdUint, LaneCount, Mask, Simd, SimdCast, SimdElement,
     SupportedLaneCount,
 };
 
@@ -70,11 +70,27 @@ pub trait SimdInt: Copy + Sealed {
     /// # #[cfg(not(feature = "as_crate"))] use core::simd;
     /// # use simd::prelude::*;
     /// use core::i32::{MIN, MAX};
-    /// let xs = Simd::from_array([MIN, MIN +1, -5, 0]);
+    /// let xs = Simd::from_array([MIN, MIN + 1, -5, 0]);
     /// assert_eq!(xs.abs(), Simd::from_array([MIN, MAX, 5, 0]));
     /// ```
     fn abs(self) -> Self;
 
+    /// Lanewise absolute difference.
+    /// Every element becomes the absolute difference of `self` and `second`.
+    ///
+    /// # Examples
+    /// ```
+    /// # #![feature(portable_simd)]
+    /// # #[cfg(feature = "as_crate")] use core_simd::simd;
+    /// # #[cfg(not(feature = "as_crate"))] use core::simd;
+    /// # use simd::prelude::*;
+    /// use core::i32::{MIN, MAX};
+    /// let a = Simd::from_array([MIN, MAX, 100, -100]);
+    /// let b = Simd::from_array([MAX, MIN, -80, -120]);
+    /// assert_eq!(a.abs_diff(b), Simd::from_array([u32::MAX, u32::MAX, 180, 20]));
+    /// ```
+    fn abs_diff(self, second: Self) -> Self::Unsigned;
+
     /// Lanewise saturating absolute value, implemented in Rust.
     /// As abs(), except the MIN value becomes MAX instead of itself.
     ///
@@ -259,6 +275,13 @@ macro_rules! impl_trait {
                 (self^m) - m
             }
 
+            #[inline]
+            fn abs_diff(self, second: Self) -> Self::Unsigned {
+                let max = self.simd_max(second);
+                let min = self.simd_min(second);
+                (max - min).cast()
+            }
+
             #[inline]
             fn saturating_abs(self) -> Self {
                 // arith shift for -1 or 0 mask based on sign bit, giving 2s complement

crates/core_simd/src/simd/num/uint.rs

@@ -1,5 +1,5 @@
 use super::sealed::Sealed;
-use crate::simd::{LaneCount, Simd, SimdCast, SimdElement, SupportedLaneCount};
+use crate::simd::{cmp::SimdOrd, LaneCount, Simd, SimdCast, SimdElement, SupportedLaneCount};
 
 /// Operations on SIMD vectors of unsigned integers.
 pub trait SimdUint: Copy + Sealed {
@@ -57,6 +57,22 @@ pub trait SimdUint: Copy + Sealed {
     /// assert_eq!(sat, Simd::splat(0));
     fn saturating_sub(self, second: Self) -> Self;
 
+    /// Lanewise absolute difference.
+    /// Every element becomes the absolute difference of `self` and `second`.
+    ///
+    /// # Examples
+    /// ```
+    /// # #![feature(portable_simd)]
+    /// # #[cfg(feature = "as_crate")] use core_simd::simd;
+    /// # #[cfg(not(feature = "as_crate"))] use core::simd;
+    /// # use simd::prelude::*;
+    /// use core::u32::MAX;
+    /// let a = Simd::from_array([0, MAX, 100, 20]);
+    /// let b = Simd::from_array([MAX, 0, 80, 200]);
+    /// assert_eq!(a.abs_diff(b), Simd::from_array([MAX, MAX, 20, 180]));
+    /// ```
+    fn abs_diff(self, second: Self) -> Self;
+
     /// Returns the sum of the elements of the vector, with wrapping addition.
     fn reduce_sum(self) -> Self::Scalar;
 
@@ -138,6 +154,13 @@ macro_rules! impl_trait {
                 unsafe { core::intrinsics::simd::simd_saturating_sub(self, second) }
             }
 
+            #[inline]
+            fn abs_diff(self, second: Self) -> Self {
+                let max = self.simd_max(second);
+                let min = self.simd_min(second);
+                max - min
+            }
+
             #[inline]
             fn reduce_sum(self) -> Self::Scalar {
                 // Safety: `self` is an integer vector

crates/core_simd/tests/abs_diff.rs

@@ -0,0 +1,33 @@
+#![feature(portable_simd)]
+
+use core_simd::simd::Simd;
+
+const LANES: usize = 16;
+
+#[test]
+fn abs_diff_i8() {
+    use core_simd::simd::num::SimdInt;
+
+    for x in i8::MIN..=i8::MAX {
+        for y in i8::MIN..=i8::MAX {
+            let left: Simd<u8, LANES> = Simd::splat(x.abs_diff(y));
+            let right = Simd::splat(x).abs_diff(Simd::splat(y));
+
+            assert_eq!(left, right);
+        }
+    }
+}
+
+#[test]
+fn abs_diff_u8() {
+    use core_simd::simd::num::SimdUint;
+
+    for x in u8::MIN..=u8::MAX {
+        for y in u8::MIN..=u8::MAX {
+            let left: Simd<u8, LANES> = Simd::splat(x.abs_diff(y));
+            let right = Simd::splat(x).abs_diff(Simd::splat(y));
+
+            assert_eq!(left, right);
+        }
+    }
+}