rten_simd/

ops.rs

//! Traits for operations on SIMD vectors.
//!
//! The entry point is the [`Isa`] trait, an implementation of which is passed
//! to SIMD operations when evaluated. This has methods for each of the
//! supported element types which returns the implementation of operations on
//! SIMD vectors with that element type.
//!
//! The [`NumOps`] trait provides operations available on all element types. The
//! sub-traits [`FloatOps`] and [`SignedIntOps`] provide additional operations
//! on float and signed integer element types. Additionally there are traits for
//! individual operations such as [`Extend`] or [`NarrowSaturate`] which are
//! available on a subset of element types.

use std::mem::MaybeUninit;

use crate::elem::Elem;
use crate::simd::{Mask, Simd};

/// Entry point for performing SIMD operations using a particular Instruction
/// Set Architecture (ISA).
///
/// Implementations of this trait are types which can only be instantiated
/// if the instruction set is available. They are usually zero-sized and thus
/// free to copy.
///
/// # Safety
///
/// Implementations must ensure they can only be constructed if the
/// instruction set is supported on the current system.
pub unsafe trait Isa: Copy {
    /// SIMD vector with an unspecified element type. This is used for
    /// bitwise casting between different vector types.
    type Bits: Simd;

    /// Mask vector for 32-bit lanes.
    type M32: Mask;

    /// Mask vector for 16-bit lanes.
    type M16: Mask;

    /// Mask vector for 8-bit lanes.
    type M8: Mask;

    /// SIMD vector with `f32` elements.
    type F32: Simd<Elem = f32, Isa = Self, Mask = Self::M32>;

    /// SIMD vector with `i32` elements.
    type I32: Simd<Elem = i32, Isa = Self, Mask = Self::M32>;

    /// SIMD vector with `i16` elements.
    type I16: Simd<Elem = i16, Isa = Self, Mask = Self::M16>;

    /// SIMD vector with `i8` elements.
    type I8: Simd<Elem = i8, Isa = Self, Mask = Self::M8>;

    /// SIMD vector with `u8` elements.
    type U8: Simd<Elem = u8, Isa = Self, Mask = Self::M8>;

    /// SIMD vector with `u16` elements.
    type U16: Simd<Elem = u16, Isa = Self, Mask = Self::M16>;

    /// SIMD vector with `u32` elements.
    type U32: Simd<Elem = u32, Isa = Self, Mask = Self::M32>;

    /// Operations on SIMD vectors with `f32` elements.
    fn f32(self) -> impl FloatOps<f32, Simd = Self::F32, Int = Self::I32>;

    /// Operations on SIMD vectors with `i32` elements.
    fn i32(
        self,
    ) -> impl SignedIntOps<i32, Simd = Self::I32>
    + NarrowSaturate<i32, i16, Output = Self::I16>
    + Concat<i32>
    + ToFloat<i32, Output = Self::F32>;

    /// Operations on SIMD vectors with `i16` elements.
    fn i16(
        self,
    ) -> impl SignedIntOps<i16, Simd = Self::I16>
    + NarrowSaturate<i16, u8, Output = Self::U8>
    + Extend<i16, Output = Self::I32>
    + Interleave<i16>;

    /// Operations on SIMD vectors with `i8` elements.
    fn i8(
        self,
    ) -> impl SignedIntOps<i8, Simd = Self::I8> + Extend<i8, Output = Self::I16> + Interleave<i8>;

    /// Operations on SIMD vectors with `u8` elements.
    fn u8(
        self,
    ) -> impl IntOps<u8, Simd = Self::U8> + Extend<u8, Output = Self::U16> + Interleave<u8>;

    /// Operations on SIMD vectors with `u16` elements.
    fn u16(self) -> impl IntOps<u16, Simd = Self::U16>;

    /// Operations on mask vectors for 32-bit lanes.
    fn m32(self) -> impl MaskOps<Self::M32>;

    /// Operations on mask vectors for 16-bit lanes.
    fn m16(self) -> impl MaskOps<Self::M16>;

    /// Operations on mask vectors for 8-bit lanes.
    fn m8(self) -> impl MaskOps<Self::M8>;
}

/// Get the [`NumOps`] implementation from an [`Isa`] for a given element type.
///
/// This trait is useful for writing SIMD operations which are generic over the
/// element type. It is implemented for all of the element types supported in
/// SIMD vectors.
///
/// # Example
///
/// This example shows how to use [`GetNumOps`] to write a vectorized `Sum`
/// operation.
///
/// ```
/// use rten_simd::{Isa, SimdIterable, SimdOp};
/// use rten_simd::ops::{GetNumOps, NumOps};
///
/// struct Sum<'a, T>(&'a [T]);
///
/// impl<T: std::ops::Add<Output=T> + GetNumOps> SimdOp for Sum<'_, T> {
///   type Output = T;
///   
///   #[inline(always)]
///   fn eval<I: Isa>(self, isa: I) -> Self::Output {
///     let ops = T::num_ops(isa);
///
///     // Build `ops.len()` partial sums in parallel. If the slice length is
///     // not a multiple of `ops.len()` it will be padded with zeros.
///     let mut sum = ops.zero();
///     for chunk in self.0.simd_iter_pad(ops) {
///         sum = ops.add(sum, chunk);
///     }
///
///     // Horizontally reduce the SIMD vector containing partial sums to a
///     // single value.
///     ops.sum(sum)
///   }
/// }
///
/// let vals: Vec<_> = (1..20i32).collect();
/// let sum = Sum(&vals).dispatch();
/// assert_eq!(sum, vals.iter().sum());
/// ```
pub trait GetNumOps
where
    Self: GetSimd + 'static,
{
    /// Return the [`NumOps`] implementation from a SIMD [`Isa`] that provides
    /// operations on vectors containing elements of type `Self`.
    fn num_ops<I: Isa>(isa: I) -> impl NumOps<Self, Simd = Self::Simd<I>>;
}

macro_rules! impl_get_ops {
    ($trait:ty, $method:ident, $ops:ident, $type:ident) => {
        impl $trait for $type {
            fn $method<I: Isa>(isa: I) -> impl $ops<Self, Simd = <Self as GetSimd>::Simd<I>> {
                isa.$type()
            }
        }
    };
}
impl_get_ops!(GetNumOps, num_ops, NumOps, f32);
impl_get_ops!(GetNumOps, num_ops, NumOps, i16);
impl_get_ops!(GetNumOps, num_ops, NumOps, i32);
impl_get_ops!(GetNumOps, num_ops, NumOps, i8);
impl_get_ops!(GetNumOps, num_ops, NumOps, u16);
impl_get_ops!(GetNumOps, num_ops, NumOps, u8);

/// Get the [`Simd`] implementation from an [`Isa`] for a given element type.
///
/// For example the type `<f32 as GetSimd>::Simd<I>` yields `I::F32` where
/// `I` is an `Isa`. This trait is used for example by
/// [`SimdUnaryOp`](crate::SimdUnaryOp) to determine the type of SIMD vector
/// that corresponds to the element type.
pub trait GetSimd: Elem {
    type Simd<I: Isa>: Simd<Elem = Self, Isa = I>;
}

macro_rules! impl_getsimd {
    ($ty:ty, $simd:ident) => {
        impl GetSimd for $ty {
            type Simd<I: Isa> = I::$simd;
        }
    };
}
impl_getsimd!(f32, F32);
impl_getsimd!(i16, I16);
impl_getsimd!(i32, I32);
impl_getsimd!(i8, I8);
impl_getsimd!(u16, U16);
impl_getsimd!(u8, U8);

/// Get the [`FloatOps`] implementation from an [`Isa`] for a given element type.
///
/// This is a specialization of [`GetNumOps`] for float element types.
pub trait GetFloatOps
where
    Self: GetSimd,
{
    fn float_ops<I: Isa>(isa: I) -> impl FloatOps<Self, Simd = Self::Simd<I>>;
}
impl_get_ops!(GetFloatOps, float_ops, FloatOps, f32);

/// Get the [`IntOps`] implementation from an [`Isa`] for a given element type.
///
/// This is a specialization of [`GetNumOps`] for signed integer element types.
pub trait GetIntOps
where
    Self: GetSimd,
{
    fn int_ops<I: Isa>(isa: I) -> impl IntOps<Self, Simd = Self::Simd<I>>;
}
impl_get_ops!(GetIntOps, int_ops, IntOps, i16);
impl_get_ops!(GetIntOps, int_ops, IntOps, i32);
impl_get_ops!(GetIntOps, int_ops, IntOps, i8);
impl_get_ops!(GetIntOps, int_ops, IntOps, u8);
impl_get_ops!(GetIntOps, int_ops, IntOps, u16);

/// Get the [`SignedIntOps`] implementation from an [`Isa`] for a given element type.
///
/// This is a specialization of [`GetNumOps`] for signed integer element types.
pub trait GetSignedIntOps
where
    Self: GetSimd,
{
    fn signed_int_ops<I: Isa>(isa: I) -> impl SignedIntOps<Self, Simd = Self::Simd<I>>;
}
impl_get_ops!(GetSignedIntOps, signed_int_ops, SignedIntOps, i32);
impl_get_ops!(GetSignedIntOps, signed_int_ops, SignedIntOps, i16);
impl_get_ops!(GetSignedIntOps, signed_int_ops, SignedIntOps, i8);

/// SIMD operations on a [`Mask`] vector.
///
/// # Safety
///
/// Implementations must ensure they can only be constructed if the
/// instruction set is supported on the current system.
pub unsafe trait MaskOps<M: Mask>: Copy {
    /// Compute `x & y`.
    fn and(self, x: M, y: M) -> M;

    /// Return true if any lanes are true.
    fn any(self, x: M) -> bool;

    /// Return true if all lanes are false.
    fn all_false(self, x: M) -> bool {
        !self.any(x)
    }

    /// Return true if all lanes are true.
    fn all(self, x: M) -> bool;
}

/// Operations available on all SIMD vector types.
///
/// This trait provides core operations available on all SIMD vector types.
///
/// - Load from and store into memory
/// - Creating a new vector filled with zeros or a specific value
/// - Combining elements from two vectors according to a mask
/// - Add, subtract and multiply
/// - Comparison (equality, less than, greater than etc.)
///
/// # Safety
///
/// Implementations must ensure they can only be constructed if the
/// instruction set is supported on the current system.
#[allow(clippy::len_without_is_empty)]
pub unsafe trait NumOps<T: Elem>: Copy {
    /// SIMD vector containing lanes of type `T`.
    type Simd: Simd<Elem = T>;

    /// Convert `x` to an untyped vector of the same width.
    #[allow(clippy::wrong_self_convention)]
    fn from_bits(self, x: <<Self::Simd as Simd>::Isa as Isa>::Bits) -> Self::Simd {
        Self::Simd::from_bits(x)
    }

    /// Return the number of elements in the vector.
    fn len(self) -> usize;

    /// Compute `x + y`.
    fn add(self, x: Self::Simd, y: Self::Simd) -> Self::Simd;

    /// Compute `x - y`.
    fn sub(self, x: Self::Simd, y: Self::Simd) -> Self::Simd;

    /// Compute `x * y`.
    fn mul(self, x: Self::Simd, y: Self::Simd) -> Self::Simd;

    /// Create a new vector with all lanes set to zero.
    fn zero(self) -> Self::Simd {
        self.splat(T::default())
    }

    /// Create a new vector with all lanes set to one.
    fn one(self) -> Self::Simd {
        self.splat(T::one())
    }

    /// Compute `a * b + c`.
    ///
    /// This will use fused multiply-add instructions if available. For float
    /// element types, this may use one or two roundings.
    fn mul_add(self, a: Self::Simd, b: Self::Simd, c: Self::Simd) -> Self::Simd {
        self.add(self.mul(a, b), c)
    }

    /// Broadcast the element from one lane of a vector to all lanes of a new
    /// vector.
    fn broadcast_lane<const LANE: i32>(self, x: Self::Simd) -> Self::Simd {
        let val = x.to_array()[LANE as usize];
        self.splat(val)
    }

    /// Evaluate a polynomial using Horner's method.
    ///
    /// Computes `x * coeffs[0] + x^2 * coeffs[1] ... x^n * coeffs[N]`
    #[inline]
    fn poly_eval(self, x: Self::Simd, coeffs: &[Self::Simd]) -> Self::Simd {
        let mut y = coeffs[coeffs.len() - 1];
        for i in (0..coeffs.len() - 1).rev() {
            y = self.mul_add(y, x, coeffs[i]);
        }
        self.mul(y, x)
    }

    /// Return a mask indicating whether elements in `x` are less than `y`.
    #[inline]
    fn lt(self, x: Self::Simd, y: Self::Simd) -> <Self::Simd as Simd>::Mask {
        self.gt(y, x)
    }

    /// Return a mask indicating whether elements in `x` are less or equal to `y`.
    #[inline]
    fn le(self, x: Self::Simd, y: Self::Simd) -> <Self::Simd as Simd>::Mask {
        self.ge(y, x)
    }

    /// Return a mask indicating whether elements in `x` are equal to `y`.
    fn eq(self, x: Self::Simd, y: Self::Simd) -> <Self::Simd as Simd>::Mask;

    /// Return a mask indicating whether elements in `x` are greater or equal to `y`.
    fn ge(self, x: Self::Simd, y: Self::Simd) -> <Self::Simd as Simd>::Mask;

    /// Return a mask indicating whether elements in `x` are greater than `y`.
    fn gt(self, x: Self::Simd, y: Self::Simd) -> <Self::Simd as Simd>::Mask;

    /// Return the minimum of `x` and `y` for each lane.
    fn min(self, x: Self::Simd, y: Self::Simd) -> Self::Simd {
        self.select(x, y, self.le(x, y))
    }

    /// Return the maximum of `x` and `y` for each lane.
    fn max(self, x: Self::Simd, y: Self::Simd) -> Self::Simd {
        self.select(x, y, self.ge(x, y))
    }

    /// Clamp values in `x` to minimum and maximum values from corresponding
    /// lanes in `min` and `max`.
    fn clamp(self, x: Self::Simd, min: Self::Simd, max: Self::Simd) -> Self::Simd {
        self.min(self.max(x, min), max)
    }

    /// Return the bitwise AND of `x` and `y`.
    fn and(self, x: Self::Simd, y: Self::Simd) -> Self::Simd;

    /// Return the bitwise NOT of `x`.
    fn not(self, x: Self::Simd) -> Self::Simd;

    /// Return the bitwise OR of `x` and `y`.
    fn or(self, x: Self::Simd, y: Self::Simd) -> Self::Simd;

    /// Return the bitwise XOR of `x` and `y`.
    fn xor(self, x: Self::Simd, y: Self::Simd) -> Self::Simd;

    /// Create a new vector with all lanes set to `x`.
    fn splat(self, x: T) -> Self::Simd;

    /// Reduce the elements in `x` to a single value using `f`, then
    /// return a new vector with the accumulated value broadcast to each lane.
    #[inline]
    fn fold_splat<F: Fn(T, T) -> T>(self, x: Self::Simd, accum: T, f: F) -> Self::Simd {
        let reduced = x.to_array().into_iter().fold(accum, f);
        self.splat(reduced)
    }

    /// Return a mask with the first `n` lanes set to true.
    fn first_n_mask(self, n: usize) -> <Self::Simd as Simd>::Mask;

    /// Load the first `self.len()` elements from a slice into a vector.
    ///
    /// Panics if `xs.len() < self.len()`.
    #[inline]
    #[track_caller]
    fn load(self, xs: &[T]) -> Self::Simd {
        assert!(
            xs.len() >= self.len(),
            "slice length {} too short for SIMD vector width {}",
            xs.len(),
            self.len()
        );
        unsafe { self.load_ptr(xs.as_ptr()) }
    }

    /// Load `N` vectors from consecutive sub-slices of `xs`.
    ///
    /// Panics if `xs.len() < self.len() * N`.
    #[inline]
    #[track_caller]
    fn load_many<const N: usize>(self, xs: &[T]) -> [Self::Simd; N] {
        let v_len = self.len();
        assert!(
            xs.len() >= v_len * N,
            "slice length {} too short for {} * SIMD vector width {}",
            xs.len(),
            N,
            v_len
        );
        // Safety: `xs.add(i * v_len)` points to at least `v_len` elements.
        std::array::from_fn(|i| unsafe { self.load_ptr(xs.as_ptr().add(i * v_len)) })
    }

    /// Load elements from `xs` into a vector.
    ///
    /// If the vector length exceeds `xs.len()`, the tail is padded with zeros.
    ///
    /// Returns the padded vector and a mask of the lanes which were set.
    #[inline]
    fn load_pad(self, xs: &[T]) -> (Self::Simd, <Self::Simd as Simd>::Mask) {
        let n = xs.len().min(self.len());
        let mask = self.first_n_mask(n);

        // Safety: `xs.add(i)` is valid for all positions where mask is set
        let vec = unsafe { self.load_ptr_mask(xs.as_ptr(), mask) };

        (vec, mask)
    }

    /// Load vector of elements from `ptr`.
    ///
    /// `ptr` is not required to have any particular alignment.
    ///
    /// # Safety
    ///
    /// `ptr` must point to `self.len()` initialized elements of type `T`.
    unsafe fn load_ptr(self, ptr: *const T) -> Self::Simd;

    /// Load vector elements from `ptr` using a mask.
    ///
    /// `ptr` is not required to have any particular alignment.
    ///
    /// # Safety
    ///
    /// For each mask position `i` which is true, `ptr.add(i)` must point to
    /// an initialized element of type `T`.
    unsafe fn load_ptr_mask(self, ptr: *const T, mask: <Self::Simd as Simd>::Mask) -> Self::Simd;

    /// Select elements from `x` or `y` according to a mask.
    ///
    /// Elements are selected from `x` where the corresponding mask element
    /// is one or `y` if zero.
    fn select(self, x: Self::Simd, y: Self::Simd, mask: <Self::Simd as Simd>::Mask) -> Self::Simd;

    /// Store the values in this vector to a memory location.
    ///
    /// # Safety
    ///
    /// `ptr` must point to `self.len()` elements.
    unsafe fn store_ptr(self, x: Self::Simd, ptr: *mut T);

    /// Store `x` into the first `self.len()` elements of `xs`.
    #[inline]
    fn store(self, x: Self::Simd, xs: &mut [T]) {
        assert!(xs.len() >= self.len());
        unsafe { self.store_ptr(x, xs.as_mut_ptr()) }
    }

    /// Store `x` into the first `self.len()` elements of `xs`.
    ///
    /// This is a variant of [`store`](NumOps::store) which takes an
    /// uninitialized slice as input and returns the initialized portion of the
    /// slice.
    #[inline]
    fn store_uninit(self, x: Self::Simd, xs: &mut [MaybeUninit<T>]) -> &mut [T] {
        let len = self.len();
        let xs_ptr = xs.as_mut_ptr() as *mut T;
        assert!(xs.len() >= len);
        unsafe {
            self.store_ptr(x, xs_ptr);

            // Safety: `store_ptr` initialized `len` elements of `xs`.
            std::slice::from_raw_parts_mut(xs_ptr, len)
        }
    }

    /// Store the values in this vector to a memory location, where the
    /// corresponding mask element is set.
    ///
    /// # Safety
    ///
    /// For each position `i` in the mask which is true, `ptr.add(i)` must point
    /// to a valid element of type `Self::Elem`.
    unsafe fn store_ptr_mask(self, x: Self::Simd, ptr: *mut T, mask: <Self::Simd as Simd>::Mask);

    /// Pre-fetch the cache line containing `ptr` for reading.
    fn prefetch(self, ptr: *const T) {
        // Default implementation does nothing
        let _ = ptr;
    }

    /// Pre-fetch the cache line containing `ptr` for writing.
    fn prefetch_write(self, ptr: *mut T) {
        // Default implementation does nothing
        let _ = ptr;
    }

    /// Horizontally sum the elements in a vector.
    ///
    /// If the sum overflows, it will wrap. This choice was made to enable
    /// consistency between native intrinsics for horizontal addition and the
    /// generic implementation.
    fn sum(self, x: Self::Simd) -> T {
        let mut sum = T::default();
        for elem in x.to_array() {
            sum = sum.wrapping_add(elem);
        }
        sum
    }
}

/// Operations available on SIMD vectors with float elements.
pub trait FloatOps<T: Elem>: NumOps<T> {
    /// Integer SIMD vector of the same bit-width as this vector.
    type Int: Simd;

    /// Compute x / y
    fn div(self, x: Self::Simd, y: Self::Simd) -> Self::Simd;

    /// Compute 1. / x
    fn reciprocal(self, x: Self::Simd) -> Self::Simd {
        self.div(self.one(), x)
    }

    /// Compute `-x`
    fn neg(self, x: Self::Simd) -> Self::Simd {
        self.sub(self.zero(), x)
    }

    /// Compute the absolute value of `x`
    fn abs(self, x: Self::Simd) -> Self::Simd {
        self.select(self.neg(x), x, self.lt(x, self.zero()))
    }

    /// Round `x` to the nearest integer value, with ties to even.
    ///
    /// This is like [`f32::round_ties_even`].
    fn round_ties_even(self, x: Self::Simd) -> Self::Simd;

    /// Compute `c - a * b`.
    fn mul_sub_from(self, a: Self::Simd, b: Self::Simd, c: Self::Simd) -> Self::Simd {
        self.sub(c, self.mul(a, b))
    }

    /// Convert each lane to an integer of the same width, rounding towards zero.
    fn to_int_trunc(self, x: Self::Simd) -> Self::Int;

    /// Convert each lane to an integer of the same width, rounding to nearest
    /// with ties to even.
    fn to_int_round(self, x: Self::Simd) -> Self::Int;
}

/// Operations on SIMD vectors with integer elements.
pub trait IntOps<T: Elem>: NumOps<T> {
    /// Shift each lane in `x` left by `SHIFT` bits.
    fn shift_left<const SHIFT: i32>(self, x: Self::Simd) -> Self::Simd;

    /// Shift each lane in `x` right by `SHIFT` bits.
    ///
    /// For signed integer types this is an arithmetic shift, so shifting a
    /// negative number right will preserve the sign, like the `>>` operator.
    fn shift_right<const SHIFT: i32>(self, x: Self::Simd) -> Self::Simd;
}

/// Operations on SIMD vectors with signed integer elements.
pub trait SignedIntOps<T: Elem>: IntOps<T> {
    /// Compute the absolute value of `x`
    fn abs(self, x: Self::Simd) -> Self::Simd {
        self.select(self.neg(x), x, self.lt(x, self.zero()))
    }

    /// Return `-x`.
    fn neg(self, x: Self::Simd) -> Self::Simd {
        self.sub(self.zero(), x)
    }
}

/// Widen lanes to a type with twice the width.
///
/// For integer types, the extended type has the same signed-ness.
pub trait Extend<T: Elem>: NumOps<T> {
    /// SIMD vector type with elements that have twice the bit-width of
    /// those in `Self::SIMD`.
    type Output;

    /// Extend each lane to a type with twice the width.
    ///
    /// Returns a tuple containing the extended low and high half of the input.
    fn extend(self, x: Self::Simd) -> (Self::Output, Self::Output);
}

/// Interleave elements from the low or high halves of two vectors to form a
/// new vector.
pub trait Interleave<T: Elem>: NumOps<T> {
    /// Interleave elements from the low halves of two vectors.
    fn interleave_low(self, a: Self::Simd, b: Self::Simd) -> Self::Simd;

    /// Interleave elements from the high halves of two vectors.
    fn interleave_high(self, a: Self::Simd, b: Self::Simd) -> Self::Simd;
}

/// Concatenate elements from the low or high halves of two vectors to form a
/// new vector.
pub trait Concat<T: Elem>: NumOps<T> {
    /// Concatenate elements from the low halves of two vectors.
    fn concat_low(self, a: Self::Simd, b: Self::Simd) -> Self::Simd;

    /// Concatenate elements from the high halves of two vectors.
    fn concat_high(self, a: Self::Simd, b: Self::Simd) -> Self::Simd;
}

/// Convert each lane to a float with the same bit width.
pub trait ToFloat<T: Elem>: NumOps<T> {
    type Output;

    fn to_float(self, x: Self::Simd) -> Self::Output;
}

/// Narrow lanes to one with half the bit-width, using truncation.
///
/// For integer types, the narrowed type has the same signed-ness.
#[cfg(target_arch = "x86_64")]
pub(crate) trait Narrow<S: Simd> {
    type Output;

    /// Truncate each lane in a pair of vectors to one with half the bit-width.
    ///
    /// Returns a vector containing the concatenation of the narrowed lanes
    /// from `low` followed by the narrowed lanes from `high`.
    fn narrow_truncate(self, low: S, high: S) -> Self::Output;
}

/// Narrow lanes to one with half the bit-width, using saturation.
///
/// Conceptually, this converts each element from `S1::Elem` to `S2::Elem` using
/// `x.clamp(S2::Elem::MIN as S1::Elem, S2::Elem::MAX as S1::Elem) as S2::Elem`.
pub trait NarrowSaturate<T: Elem, U: Elem>: NumOps<T> {
    type Output: Simd<Elem = U>;

    /// Narrow each lane in a pair of vectors to one with half the bit-width.
    ///
    /// Returns a vector containing the concatenation of the narrowed lanes
    /// from `low` followed by the narrowed lanes from `high`.
    fn narrow_saturate(self, low: Self::Simd, high: Self::Simd) -> Self::Output;
}

#[cfg(test)]
mod tests {
    use crate::elem::WrappingAdd;
    use crate::ops::{
        Concat, Extend, FloatOps, IntOps, Interleave, MaskOps, NarrowSaturate, NumOps,
        SignedIntOps, ToFloat,
    };
    use crate::{Isa, Mask, Simd, SimdOp, assert_simd_eq, assert_simd_ne, test_simd_op};

    // Generate tests for operations available on all numeric types.
    macro_rules! test_num_ops {
        ($modname:ident, $elem:ident, $mask_elem:ident) => {
            mod $modname {
                use super::{
                    Isa, MaskOps, NumOps, Simd, SimdOp, WrappingAdd, assert_simd_eq,
                    assert_simd_ne, test_simd_op,
                };

                #[test]
                fn test_load_store() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let src: Vec<_> = (0..ops.len() * 4).map(|x| x as $elem).collect();
                        let mut dst = vec![0 as $elem; src.len()];

                        for (src_chunk, dst_chunk) in
                            src.chunks(ops.len()).zip(dst.chunks_mut(ops.len()))
                        {
                            let x = ops.load(src_chunk);
                            ops.store(x, dst_chunk);
                        }

                        assert_eq!(dst, src);
                    })
                }

                #[test]
                fn test_store_uninit() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let src: Vec<_> = (0..ops.len() + 3).map(|x| x as $elem).collect();
                        let mut dest = Vec::with_capacity(src.len());

                        let x = ops.load(&src);

                        let init = ops.store_uninit(x, dest.spare_capacity_mut());
                        assert_eq!(init, &src[0..ops.len()]);
                    })
                }

                #[test]
                fn test_load_many() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let src: Vec<_> = (0..ops.len() * 2).map(|x| x as $elem).collect();

                        let xs = ops.load_many::<2>(&src);
                        assert_simd_eq!(xs[0], ops.load(&src));
                        assert_simd_eq!(xs[1], ops.load(&src[ops.len()..]));
                    })
                }

                #[test]
                fn test_load_pad() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        // Array which is shorter than vector length for all ISAs.
                        let src = [0, 1, 2].map(|x| x as $elem);

                        let (vec, _mask) = ops.load_pad(&src);
                        let vec_array = vec.to_array();
                        let vec_slice = vec_array.as_ref();

                        assert_eq!(&vec_slice[..src.len()], &src);
                        for i in ops.len()..vec_slice.len() {
                            assert_eq!(vec_array[i], 0 as $elem);
                        }
                    })
                }

                #[test]
                fn test_bin_ops() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let a = 2 as $elem;
                        let b = 3 as $elem;

                        let x = ops.splat(a);
                        let y = ops.splat(b);

                        // Add
                        let expected = ops.splat(a + b);
                        let actual = ops.add(x, y);
                        assert_simd_eq!(actual, expected);

                        // Sub
                        let expected = ops.splat(b - a);
                        let actual = ops.sub(y, x);
                        assert_simd_eq!(actual, expected);

                        // Mul
                        let expected = ops.splat(a * b);
                        let actual = ops.mul(x, y);
                        assert_simd_eq!(actual, expected);
                    })
                }

                #[test]
                fn test_cmp_ops() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();
                        let mo = isa.$mask_elem();

                        let x = ops.splat(1 as $elem);
                        let y = ops.splat(2 as $elem);

                        assert!(mo.all(ops.eq(x, x)));
                        assert!(mo.all_false(ops.eq(x, y)));
                        assert!(mo.all(ops.le(x, x)));
                        assert!(mo.all(ops.le(x, y)));
                        assert!(mo.all_false(ops.le(y, x)));
                        assert!(mo.all(ops.ge(x, x)));
                        assert!(mo.all_false(ops.ge(x, y)));
                        assert!(mo.all_false(ops.gt(x, y)));
                        assert!(mo.all(ops.gt(y, x)));
                    })
                }

                #[test]
                fn test_mul_add() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let a = ops.splat(2 as $elem);
                        let b = ops.splat(3 as $elem);
                        let c = ops.splat(4 as $elem);

                        let actual = ops.mul_add(a, b, c);
                        let expected = ops.splat(((2. * 3.) + 4.) as $elem);

                        assert_simd_eq!(actual, expected);
                    })
                }

                #[test]
                fn test_min_max() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let x = ops.splat(3 as $elem);

                        // Min
                        let y_min = ops.min(x, ops.splat(2 as $elem));
                        let y_min_2 = ops.min(ops.splat(2 as $elem), x);
                        assert_simd_eq!(y_min, y_min_2);
                        assert_simd_eq!(y_min, ops.splat(2 as $elem));

                        // Max
                        let y_max = ops.max(x, ops.splat(4 as $elem));
                        let y_max_2 = ops.max(ops.splat(4 as $elem), x);
                        assert_simd_eq!(y_max, y_max_2);
                        assert_simd_eq!(y_max, ops.splat(4 as $elem));

                        // Clamp
                        let y_clamped = ops.clamp(x, ops.splat(0 as $elem), ops.splat(4 as $elem));
                        assert_simd_eq!(y_clamped, ops.splat(3 as $elem));
                    })
                }

                #[test]
                fn test_and() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();
                        let zeros = ops.zero();
                        let ones = ops.not(zeros);

                        // Cast to bits here because all-ones is a NaN if elements
                        // are floats, and NaNs are not equal to themselves.
                        assert_simd_eq!(ops.and(zeros, zeros).to_bits(), zeros.to_bits());
                        assert_simd_eq!(ops.and(zeros, ones).to_bits(), zeros.to_bits());
                        assert_simd_eq!(ops.and(ones, zeros).to_bits(), zeros.to_bits());
                        assert_simd_eq!(ops.and(ones, ones).to_bits(), ones.to_bits());
                    })
                }

                #[test]
                fn test_not() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();
                        let zeros = ops.zero();
                        let ones = ops.not(zeros);
                        assert_simd_ne!(zeros, ones);

                        let zeros_2 = ops.not(ones);
                        assert_simd_eq!(zeros_2, zeros);
                    })
                }

                #[test]
                fn test_or() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();
                        let zeros = ops.zero();
                        let ones = ops.not(zeros);

                        // Cast to bits here because all-ones is a NaN if elements
                        // are floats, and NaNs are not equal to themselves.
                        assert_simd_eq!(ops.or(zeros, zeros).to_bits(), zeros.to_bits());
                        assert_simd_eq!(ops.or(zeros, ones).to_bits(), ones.to_bits());
                        assert_simd_eq!(ops.or(ones, zeros).to_bits(), ones.to_bits());
                        assert_simd_eq!(ops.or(ones, ones).to_bits(), ones.to_bits());
                    })
                }

                #[test]
                fn test_xor() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let zeros = ops.zero();
                        let ones = ops.not(zeros);

                        // Cast to bits here because all-ones is a NaN if the
                        // element type is a float, and NaNs are not equal to
                        // themselves.
                        assert_simd_eq!(ops.xor(zeros, zeros).to_bits(), zeros.to_bits());
                        assert_simd_eq!(ops.xor(ones, ones).to_bits(), zeros.to_bits());
                        assert_simd_eq!(ops.xor(zeros, ones).to_bits(), ones.to_bits());
                        assert_simd_eq!(ops.xor(ones, zeros).to_bits(), ones.to_bits());
                    })
                }

                #[test]
                fn test_sum() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let vec: Vec<_> = (0..ops.len()).map(|x| x as $elem).collect();
                        let expected = vec
                            .iter()
                            .fold(0 as $elem, |sum, x| WrappingAdd::wrapping_add(sum, *x));

                        let x = ops.load(&vec);
                        let y = ops.sum(x);

                        assert_eq!(y, expected);
                    })
                }

                #[test]
                fn test_poly_eval() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let coeffs = [2, 3, 4].map(|x| x as $elem);
                        let x = 2 as $elem;
                        let y = ops.poly_eval(ops.splat(x), &coeffs.map(|c| ops.splat(c)));

                        let expected =
                            (x * coeffs[0]) + (x * x * coeffs[1]) + (x * x * x * coeffs[2]);
                        assert_simd_eq!(y, ops.splat(expected));
                    })
                }

                #[test]
                fn test_broadcast_lane() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let vec: Vec<_> = (0..ops.len()).map(|x| x as $elem).collect();
                        let xs = ops.load(&vec);

                        let ys = ops.broadcast_lane::<0>(xs);
                        assert_simd_eq!(ops.splat(0 as $elem), ys);

                        let ys = ops.broadcast_lane::<1>(xs);
                        assert_simd_eq!(ops.splat(1 as $elem), ys);

                        let ys = ops.broadcast_lane::<2>(xs);
                        assert_simd_eq!(ops.splat(2 as $elem), ys);

                        let ys = ops.broadcast_lane::<3>(xs);
                        assert_simd_eq!(ops.splat(3 as $elem), ys);
                    });
                }
            }
        };
    }

    test_num_ops!(num_ops_f32, f32, m32);
    test_num_ops!(num_ops_i32, i32, m32);
    test_num_ops!(num_ops_i16, i16, m16);
    test_num_ops!(num_ops_i8, i8, m8);
    test_num_ops!(num_ops_u8, u8, m8);
    test_num_ops!(num_ops_u16, u16, m16);

    // Test that x8 multiply truncates result as expected.
    #[test]
    fn test_i8_mul_truncate() {
        test_simd_op!(isa, {
            let ops = isa.i8();

            let x = 17i8;
            let y = 19i8;

            let x_vec = ops.splat(x);
            let y_vec = ops.splat(y);
            let expected = ops.splat(x.wrapping_mul(y));
            let actual = ops.mul(x_vec, y_vec);

            assert_simd_eq!(actual, expected);
        })
    }

    #[test]
    fn test_u8_mul_truncate() {
        test_simd_op!(isa, {
            let ops = isa.u8();

            let x = 17u8;
            let y = 19u8;

            let x_vec = ops.splat(x);
            let y_vec = ops.splat(y);
            let expected = ops.splat(x.wrapping_mul(y));
            let actual = ops.mul(x_vec, y_vec);

            assert_simd_eq!(actual, expected);
        })
    }

    // Generate tests for operations available on all float types.
    macro_rules! test_float_ops {
        ($modname:ident, $elem:ident, $int_elem:ident) => {
            mod $modname {
                use super::{FloatOps, Isa, NumOps, Simd, SimdOp, assert_simd_eq, test_simd_op};

                #[test]
                fn test_div() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let x = ops.splat(1.);
                        let y = ops.splat(2.);
                        let expected = ops.splat(0.5);
                        let actual = ops.div(x, y);
                        assert_simd_eq!(actual, expected);
                    })
                }

                #[test]
                fn test_reciprocal() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let vals = [-5., -2., 2., 5.];
                        for v in vals {
                            let x = ops.splat(v);
                            let y = ops.reciprocal(x);
                            let expected = ops.splat(1. / v);
                            assert_simd_eq!(y, expected);
                        }
                    })
                }

                #[test]
                fn test_abs() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let vals = [-1., 0., 1.];
                        for v in vals {
                            let x = ops.splat(v);
                            let y = ops.abs(x);
                            let expected = ops.splat(v.abs());
                            assert_simd_eq!(y, expected);
                        }
                    })
                }

                #[test]
                fn test_neg() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let x = ops.splat(3 as $elem);

                        let expected = ops.splat(-3 as $elem);
                        let actual = ops.neg(x);
                        assert_simd_eq!(actual, expected);
                    })
                }

                #[test]
                fn test_mul_sub_from() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let a = ops.splat(2 as $elem);
                        let b = ops.splat(3 as $elem);
                        let c = ops.splat(4 as $elem);

                        let actual = ops.mul_sub_from(a, b, c);
                        let expected = ops.splat((-(2. * 3.) + 4.) as $elem);

                        assert_simd_eq!(actual, expected);
                    })
                }

                #[test]
                fn test_round_ties_even() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let x = ops.splat(3.5 as $elem);

                        let expected = ops.splat(4 as $elem);
                        let actual = ops.round_ties_even(x);
                        assert_simd_eq!(actual, expected);
                    })
                }

                #[test]
                fn test_to_int_trunc() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let x = ops.splat(12.345);
                        let y = ops.to_int_trunc(x);
                        let expected = isa.$int_elem().splat(12);
                        assert_simd_eq!(y, expected);
                    })
                }
            }
        };
    }

    test_float_ops!(float_ops_f32, f32, i32);

    // Generate tests for operations available on unsigned integer types.
    macro_rules! test_unsigned_int_ops {
        ($modname:ident, $elem:ident) => {
            mod $modname {
                use super::{IntOps, Isa, NumOps, Simd, SimdOp, assert_simd_eq, test_simd_op};

                #[test]
                fn test_shift_left() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let x = ops.splat(42);
                        let y = ops.shift_left::<1>(x);
                        let expected = ops.splat(42 << 1);
                        assert_simd_eq!(y, expected);
                    })
                }

                #[test]
                fn test_shift_right() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let x = ops.splat(42);
                        let y = ops.shift_right::<1>(x);
                        let expected = ops.splat(42 >> 1);
                        assert_simd_eq!(y, expected);
                    })
                }
            }
        };
    }

    test_unsigned_int_ops!(uint_ops_u16, u16);

    // Generate tests for operations available on signed integer types.
    macro_rules! test_signed_int_ops {
        ($modname:ident, $elem:ident) => {
            mod $modname {
                use super::{
                    IntOps, Isa, NumOps, SignedIntOps, Simd, SimdOp, assert_simd_eq, test_simd_op,
                };

                #[test]
                fn test_abs() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let vals = [-1, 0, 1];
                        for v in vals {
                            let x = ops.splat(v);
                            let y = ops.abs(x);
                            let expected = ops.splat(v.abs());
                            assert_simd_eq!(y, expected);
                        }
                    })
                }

                // Add / Sub / Mul with a negative argument.
                #[test]
                fn test_bin_ops_neg() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let a = -2 as $elem;
                        let b = 3 as $elem;

                        let x = ops.splat(a);
                        let y = ops.splat(b);

                        // Add
                        let expected = ops.splat(a + b);
                        let actual = ops.add(x, y);
                        assert_simd_eq!(actual, expected);

                        // Sub
                        let expected = ops.splat(b - a);
                        let actual = ops.sub(y, x);
                        assert_simd_eq!(actual, expected);

                        // Mul
                        let expected = ops.splat(a * b);
                        let actual = ops.mul(x, y);
                        assert_simd_eq!(actual, expected);
                    })
                }

                #[test]
                fn test_shift_left() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let x = ops.splat(42);
                        let y = ops.shift_left::<1>(x);
                        let expected = ops.splat(42 << 1);
                        assert_simd_eq!(y, expected);
                    })
                }

                #[test]
                fn test_shift_right() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let x = ops.splat(42);
                        let y = ops.shift_right::<1>(x);
                        let expected = ops.splat(42 >> 1);
                        assert_simd_eq!(y, expected);

                        // `shift_right` is an arithmetic right shift, so it
                        // preserves the sign.
                        let x = ops.splat(-128);
                        let y = ops.shift_right::<1>(x);
                        let expected = ops.splat(-64);
                        assert_simd_eq!(y, expected);
                    })
                }

                #[test]
                fn test_neg() {
                    test_simd_op!(isa, {
                        let ops = isa.$elem();

                        let x = ops.splat(3 as $elem);

                        let expected = ops.splat(-3 as $elem);
                        let actual = ops.neg(x);
                        assert_simd_eq!(actual, expected);
                    })
                }
            }
        };
    }

    test_signed_int_ops!(int_ops_i32, i32);
    test_signed_int_ops!(int_ops_i16, i16);
    test_signed_int_ops!(int_ops_i8, i8);

    // For small positive values, signed comparison ops will work on unsigned
    // values. Make sure we really are using unsigned comparison.
    #[test]
    fn test_cmp_gt_ge_u16() {
        test_simd_op!(isa, {
            let ops = isa.u16();
            let m16 = isa.m16();

            let x = ops.splat(i16::MAX as u16);
            let y = ops.splat(i16::MAX as u16 + 1);

            assert!(m16.all(ops.gt(y, x)));
            assert!(m16.all(ops.ge(y, x)));
        });
    }

    #[test]
    fn test_cmp_gt_ge_u8() {
        test_simd_op!(isa, {
            let ops = isa.u8();
            let m8 = isa.m8();

            let x = ops.splat(i8::MAX as u8);
            let y = ops.splat(i8::MAX as u8 + 1);

            assert!(m8.all(ops.gt(y, x)));
            assert!(m8.all(ops.ge(y, x)));
        });
    }

    macro_rules! test_mask_ops {
        ($elem_type:ident, $mask_type:ident) => {
            test_simd_op!(isa, {
                let ops = isa.$elem_type();
                let mask_ops = isa.$mask_type();

                // First-n mask
                let ones = ops.first_n_mask(ops.len());
                let zeros = ops.first_n_mask(0);
                let first = ops.first_n_mask(1);

                // Bitwise and
                assert_simd_eq!(mask_ops.and(ones, ones), ones);
                assert_simd_eq!(mask_ops.and(first, ones), first);
                assert_simd_eq!(mask_ops.and(first, zeros), zeros);

                // Any
                assert!(mask_ops.any(ones));
                assert!(mask_ops.any(first));
                assert!(!mask_ops.any(zeros));

                // All
                assert!(mask_ops.all(ones));
                assert!(!mask_ops.all(zeros));
                assert!(!mask_ops.all(first));

                // All false
                assert!(mask_ops.all_false(zeros));
                assert!(!mask_ops.all_false(ones));
                assert!(!mask_ops.all_false(first));
            });
        };
    }

    #[test]
    fn test_mask_ops_m32() {
        test_mask_ops!(i32, m32);
    }

    #[test]
    fn test_mask_ops_m16() {
        test_mask_ops!(i16, m16);
    }

    #[test]
    fn test_mask_ops_m8() {
        test_mask_ops!(i8, m8);
    }

    macro_rules! test_narrow_saturate {
        ($test_name:ident, $src:ident, $dest:ident) => {
            #[test]
            fn $test_name() {
                test_simd_op!(isa, {
                    let ops = isa.$src();

                    let src: Vec<$src> = (0..ops.len() * 2).map(|x| x as $src).collect();
                    let expected: Vec<$dest> = src
                        .iter()
                        .map(|&x| x.clamp($dest::MIN as $src, $dest::MAX as $src) as $dest)
                        .collect();

                    let x_low = ops.load(&src[..ops.len()]);
                    let x_high = ops.load(&src[ops.len()..]);
                    let y = ops.narrow_saturate(x_low, x_high);

                    assert_eq!(y.to_array().as_ref(), expected);
                });
            }
        };
    }

    test_narrow_saturate!(test_narrow_i32_i16, i32, i16);
    test_narrow_saturate!(test_narrow_u16_u8, i16, u8);

    macro_rules! test_extend {
        ($test_name:ident, $src:ident, $dest:ident) => {
            #[test]
            fn $test_name() {
                test_simd_op!(isa, {
                    let ops = isa.$src();
                    let dst_ops = isa.$dest();

                    let src: Vec<$src> = (0..ops.len()).map(|x| x as $src).collect();
                    let expected: Vec<$dest> = src.iter().map(|&x| x as $dest).collect();

                    let x = ops.load(&src);
                    let (y_low, y_high) = ops.extend(x);
                    assert_eq!(y_low.to_array().as_ref(), &expected[..dst_ops.len()]);
                    assert_eq!(y_high.to_array().as_ref(), &expected[dst_ops.len()..]);
                });
            }
        };
    }
    test_extend!(test_extend_i8_i16, i8, i16);
    test_extend!(test_extend_i16_i32, i16, i32);
    test_extend!(test_extend_u8_u16, u8, u16);

    macro_rules! test_interleave {
        ($test_name:ident, $elem:ident) => {
            #[test]
            fn $test_name() {
                test_simd_op!(isa, {
                    let ops = isa.$elem();

                    let even: Vec<_> = (0..ops.len()).map(|x| x as $elem * 2).collect();
                    let even = ops.load(&even);

                    let odd: Vec<_> = (0..ops.len()).map(|x| 1 + (x as $elem * 2)).collect();
                    let odd = ops.load(&odd);

                    let expected_low: Vec<_> = (0..ops.len()).map(|x| x as $elem).collect();
                    let expected_high: Vec<_> = (0..ops.len())
                        .map(|x| ops.len() as $elem + x as $elem)
                        .collect();

                    let y_low = ops.interleave_low(even, odd);
                    let y_high = ops.interleave_high(even, odd);
                    assert_eq!(y_low.to_array().as_ref(), expected_low);
                    assert_eq!(y_high.to_array().as_ref(), expected_high);
                });
            }
        };
    }
    test_interleave!(test_interleave_i16, i16);
    test_interleave!(test_interleave_i8, i8);
    test_interleave!(test_interleave_u8, u8);

    #[test]
    fn test_concat_i32() {
        test_simd_op!(isa, {
            let ops = isa.i32();
            let src: Vec<_> = (0..ops.len() * 2).map(|x| x as i32).collect();
            let src_a = &src[..ops.len()];
            let src_b = &src[ops.len()..];

            let half_len = ops.len() / 2;
            let expected_low: Vec<_> = (0..ops.len())
                .map(|i| {
                    if i < half_len {
                        src_a[i]
                    } else {
                        src_b[i - half_len]
                    }
                })
                .collect();
            let expected_hi: Vec<_> = (0..ops.len())
                .map(|i| {
                    if i < half_len {
                        src_a[half_len + i]
                    } else {
                        src_b[i]
                    }
                })
                .collect();

            let a = ops.load(&src_a);
            let b = ops.load(&src_b);
            let ab_lo = ops.concat_low(a, b);
            let ab_hi = ops.concat_high(a, b);

            assert_eq!(ab_lo.to_array().as_ref(), expected_low);
            assert_eq!(ab_hi.to_array().as_ref(), expected_hi);
        });
    }

    #[test]
    fn test_reinterpret_cast() {
        test_simd_op!(isa, {
            let x = 1.456f32;
            let x_i32 = x.to_bits() as i32;

            let x_vec = isa.f32().splat(x);
            let y_vec: I::I32 = x_vec.reinterpret_cast();

            let expected = isa.i32().splat(x_i32);
            assert_simd_eq!(y_vec, expected);
        })
    }

    #[test]
    fn test_to_float_i32() {
        test_simd_op!(isa, {
            let x = isa.i32().splat(42);
            let y = isa.i32().to_float(x);

            let expected = isa.f32().splat(42.0);
            assert_simd_eq!(y, expected);
        });
    }
}