Add round_ties_even to StdFloat trait

Adds `round_ties_even` using `simd_round_ties_even` intrinsic, matching
the scalar `f32::round_ties_even` / `f64::round_ties_even` API.

Closes rust-lang/portable-simd#390

Author: zRedShift

crates/core_simd/tests/round.rs

@@ -42,6 +42,14 @@ macro_rules! float_rounding_test {
                     )
                 }
 
+                fn round_ties_even<const LANES: usize>() {
+                    test_helpers::test_unary_elementwise(
+                        &Vector::<LANES>::round_ties_even,
+                        &Scalar::round_ties_even,
+                        &|_| true,
+                    )
+                }
+
                 fn fract<const LANES: usize>() {
                     test_helpers::test_unary_elementwise_flush_subnormals(
                         &Vector::<LANES>::fract,

crates/std_float/src/lib.rs

@@ -156,6 +156,14 @@ pub trait StdFloat: Sealed + Sized {
         unsafe { intrinsics::simd_trunc(self) }
     }
 
+    /// Rounds each element to the nearest integer-valued float.
+    /// Ties are resolved by rounding to the number with an even least significant digit.
+    #[must_use = "method returns a new vector and does not mutate the original value"]
+    #[inline]
+    fn round_ties_even(self) -> Self {
+        unsafe { intrinsics::simd_round_ties_even(self) }
+    }
+
     /// Returns the floating point's fractional value, with its integer part removed.
     #[must_use = "method returns a new vector and does not mutate the original value"]
     fn fract(self) -> Self;

crates/std_float/tests/float.rs

@@ -71,7 +71,7 @@ macro_rules! impl_tests {
         mod $scalar {
             use std_float::StdFloat;
 
-            unary_test! { $scalar, sqrt, ceil, floor, round, trunc }
+            unary_test! { $scalar, sqrt, ceil, floor, round, trunc, round_ties_even }
             ternary_test! { $scalar, mul_add }
 
             // https://github.com/rust-lang/miri/issues/3555