skia2/include/private/SkVx.h

/*
 * Copyright 2019 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SKVX_DEFINED
#define SKVX_DEFINED

// skvx::Vec<N,T> are SIMD vectors of N T's, a v1.5 successor to SkNx<N,T>.
//
// This time we're leaning a bit less on platform-specific intrinsics and a bit
// more on Clang/GCC vector extensions, but still keeping the option open to
// drop in platform-specific intrinsics, actually more easily than before.
//
// We've also fixed a few of the caveats that used to make SkNx awkward to work
// with across translation units.  skvx::Vec<N,T> always has N*sizeof(T) size
// and alignof(T) alignment and is safe to use across translation units freely.


// It'd be nice to not pull in any Skia headers here, in case we want to spin this file off.
#include <algorithm>         // std::min, std::max
#include <cstdint>           // intXX_t
#include <cstring>           // memcpy()
#include <cmath>             // std::ceil, std::floor, std::trunc, std::round, std::sqrt, etc.
#include <initializer_list>  // std::initializer_list

#if defined(__SSE__)
    #include <immintrin.h>
#elif defined(__ARM_NEON)
    #include <arm_neon.h>
#endif

namespace skvx {

// All Vec have the same simple memory layout, the same as `T vec[N]`.
// This gives Vec a consistent ABI, letting them pass between files compiled with
// different instruction sets (e.g. SSE2 and AVX2) without fear of ODR violation.
template <int N, typename T>
struct Vec {
    static_assert((N & (N-1)) == 0, "N must be a power of 2.");

    Vec<N/2,T> lo, hi;

    // Methods belong here in the class declaration of Vec only if:
    //   - they must be here, like constructors or operator[];
    //   - they'll definitely never want a specialized implementation.
    // Other operations on Vec should be defined outside the type.

    Vec() = default;
    Vec(T x) : lo(x), hi(x) {}

    Vec(std::initializer_list<T> xs) {
        T vals[N] = {0};
        memcpy(vals, xs.begin(), std::min(xs.size(), (size_t)N)*sizeof(T));

        lo = Vec<N/2,T>::Load(vals +   0);
        hi = Vec<N/2,T>::Load(vals + N/2);
    }

    T  operator[](int i) const { return i < N/2 ? lo[i] : hi[i-N/2]; }
    T& operator[](int i)       { return i < N/2 ? lo[i] : hi[i-N/2]; }

    static Vec Load(const void* ptr) {
        Vec v;
        memcpy(&v, ptr, sizeof(Vec));
        return v;
    }
    void store(void* ptr) const {
        memcpy(ptr, this, sizeof(Vec));
    }
};

template <typename T>
struct Vec<1,T> {
    T val;

    Vec() = default;
    Vec(T x) : val(x) {}

    Vec(std::initializer_list<T> xs) : val(xs.size() ? *xs.begin() : 0) {}

    T  operator[](int) const { return val; }
    T& operator[](int)       { return val; }

    static Vec Load(const void* ptr) {
        Vec v;
        memcpy(&v, ptr, sizeof(Vec));
        return v;
    }
    void store(void* ptr) const {
        memcpy(ptr, this, sizeof(Vec));
    }
};

#if defined(__GNUC__) && !defined(__clang__) && defined(__SSE__)
    // GCC warns about ABI changes when returning >= 32 byte vectors when -mavx is not enabled.
    // This only happens for types like VExt whose ABI we don't care about, not for Vec itself.
    #pragma GCC diagnostic ignored "-Wpsabi"
#endif

template <typename D, typename S>
static inline D bit_pun(S s) {
    static_assert(sizeof(D) == sizeof(S), "");
    D d;
    memcpy(&d, &s, sizeof(D));
    return d;
}

// Helps tamp down on the repetitive boilerplate.
#define SINT template <int N, typename T> static inline
#define SIT  template <typename T> static inline

// Translate from a value type T to its corresponding Mask, the result of a comparison.
template <typename T> struct MaskHelper { using type = T; };
template <> struct MaskHelper<float > { using type = int32_t; };
template <> struct MaskHelper<double> { using type = int64_t; };
template <typename T> using Mask = typename MaskHelper<T>::type;

// Join two Vec<N,T> into one Vec<2N,T>.
SINT Vec<2*N,T> join(Vec<N,T> lo, Vec<N,T> hi) {
    Vec<2*N,T> v;
    v.lo = lo;
    v.hi = hi;
    return v;
}

// We have two default strategies for implementing most operations:
//    1) lean on Clang/GCC vector extensions when available;
//    2) recurse to scalar portable implementations when not.
// At the end we can drop in platform-specific implementations that override either default.

#if !defined(SKNX_NO_SIMD) && (defined(__clang__) || defined(__GNUC__))

    // VExt<N,T> types have the same size as Vec<N,T> and support most operations directly.
    // N.B. VExt<N,T> alignment is N*alignof(T), stricter than Vec<N,T>'s alignof(T).
    #if defined(__clang__)
        template <int N, typename T>
        using VExt = T __attribute__((ext_vector_type(N)));

    #elif defined(__GNUC__)
        template <int N, typename T>
        struct VExtHelper {
            typedef T __attribute__((vector_size(N*sizeof(T)))) type;
        };

        template <int N, typename T>
        using VExt = typename VExtHelper<N,T>::type;

        // For some reason some (new!) versions of GCC cannot seem to deduce N in the generic
        // to_vec<N,T>() below for N=4 and T=float.  This workaround seems to help...
        static inline Vec<4,float> to_vec(VExt<4,float> v) { return bit_pun<Vec<4,float>>(v); }
    #endif

    SINT VExt<N,T> to_vext(Vec<N,T> v) { return bit_pun<VExt<N,T>>(v); }
    SINT Vec <N,T> to_vec(VExt<N,T> v) { return bit_pun<Vec <N,T>>(v); }

    SINT Vec<N,T> operator+(Vec<N,T> x, Vec<N,T> y) { return to_vec(to_vext(x) + to_vext(y)); }
    SINT Vec<N,T> operator-(Vec<N,T> x, Vec<N,T> y) { return to_vec(to_vext(x) - to_vext(y)); }
    SINT Vec<N,T> operator*(Vec<N,T> x, Vec<N,T> y) { return to_vec(to_vext(x) * to_vext(y)); }
    SINT Vec<N,T> operator/(Vec<N,T> x, Vec<N,T> y) { return to_vec(to_vext(x) / to_vext(y)); }

    SINT Vec<N,T> operator^(Vec<N,T> x, Vec<N,T> y) { return to_vec(to_vext(x) ^ to_vext(y)); }
    SINT Vec<N,T> operator&(Vec<N,T> x, Vec<N,T> y) { return to_vec(to_vext(x) & to_vext(y)); }
    SINT Vec<N,T> operator|(Vec<N,T> x, Vec<N,T> y) { return to_vec(to_vext(x) | to_vext(y)); }

    SINT Vec<N,T> operator!(Vec<N,T> x) { return to_vec(!to_vext(x)); }
    SINT Vec<N,T> operator-(Vec<N,T> x) { return to_vec(-to_vext(x)); }
    SINT Vec<N,T> operator~(Vec<N,T> x) { return to_vec(~to_vext(x)); }

    SINT Vec<N,T> operator<<(Vec<N,T> x, int bits) { return to_vec(to_vext(x) << bits); }
    SINT Vec<N,T> operator>>(Vec<N,T> x, int bits) { return to_vec(to_vext(x) >> bits); }

    SINT Vec<N, Mask<T>> operator==(Vec<N,T> x, Vec<N,T> y) { return bit_pun<Vec<N,Mask<T>>>(to_vext(x) == to_vext(y)); }
    SINT Vec<N, Mask<T>> operator!=(Vec<N,T> x, Vec<N,T> y) { return bit_pun<Vec<N,Mask<T>>>(to_vext(x) != to_vext(y)); }
    SINT Vec<N, Mask<T>> operator<=(Vec<N,T> x, Vec<N,T> y) { return bit_pun<Vec<N,Mask<T>>>(to_vext(x) <= to_vext(y)); }
    SINT Vec<N, Mask<T>> operator>=(Vec<N,T> x, Vec<N,T> y) { return bit_pun<Vec<N,Mask<T>>>(to_vext(x) >= to_vext(y)); }
    SINT Vec<N, Mask<T>> operator< (Vec<N,T> x, Vec<N,T> y) { return bit_pun<Vec<N,Mask<T>>>(to_vext(x) <  to_vext(y)); }
    SINT Vec<N, Mask<T>> operator> (Vec<N,T> x, Vec<N,T> y) { return bit_pun<Vec<N,Mask<T>>>(to_vext(x) >  to_vext(y)); }

#else

    // Either SKNX_NO_SIMD is defined, or Clang/GCC vector extensions are not available.
    // We'll implement things portably, in a way that should be easily autovectorizable.

    // N == 1 scalar implementations.
    SIT Vec<1,T> operator+(Vec<1,T> x, Vec<1,T> y) { return x.val + y.val; }
    SIT Vec<1,T> operator-(Vec<1,T> x, Vec<1,T> y) { return x.val - y.val; }
    SIT Vec<1,T> operator*(Vec<1,T> x, Vec<1,T> y) { return x.val * y.val; }
    SIT Vec<1,T> operator/(Vec<1,T> x, Vec<1,T> y) { return x.val / y.val; }

    SIT Vec<1,T> operator^(Vec<1,T> x, Vec<1,T> y) { return x.val ^ y.val; }
    SIT Vec<1,T> operator&(Vec<1,T> x, Vec<1,T> y) { return x.val & y.val; }
    SIT Vec<1,T> operator|(Vec<1,T> x, Vec<1,T> y) { return x.val | y.val; }

    SIT Vec<1,T> operator!(Vec<1,T> x) { return !x.val; }
    SIT Vec<1,T> operator-(Vec<1,T> x) { return -x.val; }
    SIT Vec<1,T> operator~(Vec<1,T> x) { return ~x.val; }

    SIT Vec<1,T> operator<<(Vec<1,T> x, int bits) { return x.val << bits; }
    SIT Vec<1,T> operator>>(Vec<1,T> x, int bits) { return x.val >> bits; }

    SIT Vec<1, Mask<T>> operator==(Vec<1,T> x, Vec<1,T> y) { return x.val == y.val ? ~0 : 0; }
    SIT Vec<1, Mask<T>> operator!=(Vec<1,T> x, Vec<1,T> y) { return x.val != y.val ? ~0 : 0; }
    SIT Vec<1, Mask<T>> operator<=(Vec<1,T> x, Vec<1,T> y) { return x.val <= y.val ? ~0 : 0; }
    SIT Vec<1, Mask<T>> operator>=(Vec<1,T> x, Vec<1,T> y) { return x.val >= y.val ? ~0 : 0; }
    SIT Vec<1, Mask<T>> operator< (Vec<1,T> x, Vec<1,T> y) { return x.val <  y.val ? ~0 : 0; }
    SIT Vec<1, Mask<T>> operator> (Vec<1,T> x, Vec<1,T> y) { return x.val >  y.val ? ~0 : 0; }

    // All default N != 1 implementations just recurse on lo and hi halves.
    SINT Vec<N,T> operator+(Vec<N,T> x, Vec<N,T> y) { return join(x.lo + y.lo, x.hi + y.hi); }
    SINT Vec<N,T> operator-(Vec<N,T> x, Vec<N,T> y) { return join(x.lo - y.lo, x.hi - y.hi); }
    SINT Vec<N,T> operator*(Vec<N,T> x, Vec<N,T> y) { return join(x.lo * y.lo, x.hi * y.hi); }
    SINT Vec<N,T> operator/(Vec<N,T> x, Vec<N,T> y) { return join(x.lo / y.lo, x.hi / y.hi); }

    SINT Vec<N,T> operator^(Vec<N,T> x, Vec<N,T> y) { return join(x.lo ^ y.lo, x.hi ^ y.hi); }
    SINT Vec<N,T> operator&(Vec<N,T> x, Vec<N,T> y) { return join(x.lo & y.lo, x.hi & y.hi); }
    SINT Vec<N,T> operator|(Vec<N,T> x, Vec<N,T> y) { return join(x.lo | y.lo, x.hi | y.hi); }

    SINT Vec<N,T> operator!(Vec<N,T> x) { return join(!x.lo, !x.hi); }
    SINT Vec<N,T> operator-(Vec<N,T> x) { return join(-x.lo, -x.hi); }
    SINT Vec<N,T> operator~(Vec<N,T> x) { return join(~x.lo, ~x.hi); }

    SINT Vec<N,T> operator<<(Vec<N,T> x, int bits) { return join(x.lo << bits, x.hi << bits); }
    SINT Vec<N,T> operator>>(Vec<N,T> x, int bits) { return join(x.lo >> bits, x.hi >> bits); }

    SINT Vec<N, Mask<T>> operator==(Vec<N,T> x, Vec<N,T> y) { return join(x.lo == y.lo, x.hi == y.hi); }
    SINT Vec<N, Mask<T>> operator!=(Vec<N,T> x, Vec<N,T> y) { return join(x.lo != y.lo, x.hi != y.hi); }
    SINT Vec<N, Mask<T>> operator<=(Vec<N,T> x, Vec<N,T> y) { return join(x.lo <= y.lo, x.hi <= y.hi); }
    SINT Vec<N, Mask<T>> operator>=(Vec<N,T> x, Vec<N,T> y) { return join(x.lo >= y.lo, x.hi >= y.hi); }
    SINT Vec<N, Mask<T>> operator< (Vec<N,T> x, Vec<N,T> y) { return join(x.lo <  y.lo, x.hi <  y.hi); }
    SINT Vec<N, Mask<T>> operator> (Vec<N,T> x, Vec<N,T> y) { return join(x.lo >  y.lo, x.hi >  y.hi); }
#endif

// Some operations we want are not expressible with Clang/GCC vector
// extensions, so we implement them using the recursive approach.

// N == 1 scalar implementations.
SIT Vec<1,T> if_then_else(Vec<1,Mask<T>> cond, Vec<1,T> t, Vec<1,T> e) {
    auto t_bits = bit_pun<Mask<T>>(t),
         e_bits = bit_pun<Mask<T>>(e);
    return bit_pun<T>( (cond.val & t_bits) | (~cond.val & e_bits) );
}

SIT bool any(Vec<1,T> x) { return x.val != 0; }
SIT bool all(Vec<1,T> x) { return x.val != 0; }

SIT T min(Vec<1,T> x) { return x.val; }
SIT T max(Vec<1,T> x) { return x.val; }

SIT Vec<1,T> min(Vec<1,T> x, Vec<1,T> y) { return std::min(x.val, y.val); }
SIT Vec<1,T> max(Vec<1,T> x, Vec<1,T> y) { return std::max(x.val, y.val); }

SIT Vec<1,T>  ceil(Vec<1,T> x) { return std:: ceil(x.val); }
SIT Vec<1,T> floor(Vec<1,T> x) { return std::floor(x.val); }
SIT Vec<1,T> trunc(Vec<1,T> x) { return std::trunc(x.val); }
SIT Vec<1,T> round(Vec<1,T> x) { return std::round(x.val); }
SIT Vec<1,T>  sqrt(Vec<1,T> x) { return std:: sqrt(x.val); }
SIT Vec<1,T>   abs(Vec<1,T> x) { return std::  abs(x.val); }

SIT Vec<1,T>   rcp(Vec<1,T> x) { return 1 / x.val; }
SIT Vec<1,T> rsqrt(Vec<1,T> x) { return rcp(sqrt(x)); }
SIT Vec<1,T>   mad(Vec<1,T> f,
                   Vec<1,T> m,
                   Vec<1,T> a) { return f*m+a; }

// All default N != 1 implementations just recurse on lo and hi halves.
SINT Vec<N,T> if_then_else(Vec<N,Mask<T>> cond, Vec<N,T> t, Vec<N,T> e) {
    return join(if_then_else(cond.lo, t.lo, e.lo),
                if_then_else(cond.hi, t.hi, e.hi));
}

SINT bool any(Vec<N,T> x) { return any(x.lo) || any(x.hi); }
SINT bool all(Vec<N,T> x) { return all(x.lo) && all(x.hi); }

SINT T min(Vec<N,T> x) { return std::min(min(x.lo), min(x.hi)); }
SINT T max(Vec<N,T> x) { return std::max(max(x.lo), max(x.hi)); }

SINT Vec<N,T> min(Vec<N,T> x, Vec<N,T> y) { return join(min(x.lo, y.lo), min(x.hi, y.hi)); }
SINT Vec<N,T> max(Vec<N,T> x, Vec<N,T> y) { return join(max(x.lo, y.lo), max(x.hi, y.hi)); }

SINT Vec<N,T>  ceil(Vec<N,T> x) { return join( ceil(x.lo),  ceil(x.hi)); }
SINT Vec<N,T> floor(Vec<N,T> x) { return join(floor(x.lo), floor(x.hi)); }
SINT Vec<N,T> trunc(Vec<N,T> x) { return join(trunc(x.lo), trunc(x.hi)); }
SINT Vec<N,T> round(Vec<N,T> x) { return join(round(x.lo), round(x.hi)); }
SINT Vec<N,T>  sqrt(Vec<N,T> x) { return join( sqrt(x.lo),  sqrt(x.hi)); }
SINT Vec<N,T>   abs(Vec<N,T> x) { return join(  abs(x.lo),   abs(x.hi)); }

SINT Vec<N,T>   rcp(Vec<N,T> x) { return join(  rcp(x.lo),   rcp(x.hi)); }
SINT Vec<N,T> rsqrt(Vec<N,T> x) { return join(rsqrt(x.lo), rsqrt(x.hi)); }
SINT Vec<N,T>   mad(Vec<N,T> f,
                    Vec<N,T> m,
                    Vec<N,T> a) { return join(mad(f.lo, m.lo, a.lo), mad(f.hi, m.hi, a.hi)); }


// Scalar/vector operations just splat the scalar to a vector...
SINT Vec<N,T>       operator+ (T x, Vec<N,T> y) { return Vec<N,T>(x) +  y; }
SINT Vec<N,T>       operator- (T x, Vec<N,T> y) { return Vec<N,T>(x) -  y; }
SINT Vec<N,T>       operator* (T x, Vec<N,T> y) { return Vec<N,T>(x) *  y; }
SINT Vec<N,T>       operator/ (T x, Vec<N,T> y) { return Vec<N,T>(x) /  y; }
SINT Vec<N,T>       operator^ (T x, Vec<N,T> y) { return Vec<N,T>(x) ^  y; }
SINT Vec<N,T>       operator& (T x, Vec<N,T> y) { return Vec<N,T>(x) &  y; }
SINT Vec<N,T>       operator| (T x, Vec<N,T> y) { return Vec<N,T>(x) |  y; }
SINT Vec<N,Mask<T>> operator==(T x, Vec<N,T> y) { return Vec<N,T>(x) == y; }
SINT Vec<N,Mask<T>> operator!=(T x, Vec<N,T> y) { return Vec<N,T>(x) != y; }
SINT Vec<N,Mask<T>> operator<=(T x, Vec<N,T> y) { return Vec<N,T>(x) <= y; }
SINT Vec<N,Mask<T>> operator>=(T x, Vec<N,T> y) { return Vec<N,T>(x) >= y; }
SINT Vec<N,Mask<T>> operator< (T x, Vec<N,T> y) { return Vec<N,T>(x) <  y; }
SINT Vec<N,Mask<T>> operator> (T x, Vec<N,T> y) { return Vec<N,T>(x) >  y; }
SINT Vec<N,T>              min(T x, Vec<N,T> y) { return min(Vec<N,T>(x), y); }
SINT Vec<N,T>              max(T x, Vec<N,T> y) { return max(Vec<N,T>(x), y); }

// ... and same deal for vector/scalar operations.
SINT Vec<N,T>       operator+ (Vec<N,T> x, T y) { return x +  Vec<N,T>(y); }
SINT Vec<N,T>       operator- (Vec<N,T> x, T y) { return x -  Vec<N,T>(y); }
SINT Vec<N,T>       operator* (Vec<N,T> x, T y) { return x *  Vec<N,T>(y); }
SINT Vec<N,T>       operator/ (Vec<N,T> x, T y) { return x /  Vec<N,T>(y); }
SINT Vec<N,T>       operator^ (Vec<N,T> x, T y) { return x ^  Vec<N,T>(y); }
SINT Vec<N,T>       operator& (Vec<N,T> x, T y) { return x &  Vec<N,T>(y); }
SINT Vec<N,T>       operator| (Vec<N,T> x, T y) { return x |  Vec<N,T>(y); }
SINT Vec<N,Mask<T>> operator==(Vec<N,T> x, T y) { return x == Vec<N,T>(y); }
SINT Vec<N,Mask<T>> operator!=(Vec<N,T> x, T y) { return x != Vec<N,T>(y); }
SINT Vec<N,Mask<T>> operator<=(Vec<N,T> x, T y) { return x <= Vec<N,T>(y); }
SINT Vec<N,Mask<T>> operator>=(Vec<N,T> x, T y) { return x >= Vec<N,T>(y); }
SINT Vec<N,Mask<T>> operator< (Vec<N,T> x, T y) { return x <  Vec<N,T>(y); }
SINT Vec<N,Mask<T>> operator> (Vec<N,T> x, T y) { return x >  Vec<N,T>(y); }
SINT Vec<N,T>              min(Vec<N,T> x, T y) { return min(x, Vec<N,T>(y)); }
SINT Vec<N,T>              max(Vec<N,T> x, T y) { return max(x, Vec<N,T>(y)); }

// All vector/scalar combinations for mad() with at least one vector.
SINT Vec<N,T> mad(T f, Vec<N,T> m, Vec<N,T> a) { return Vec<N,T>(f)*m + a; }
SINT Vec<N,T> mad(Vec<N,T> f, T m, Vec<N,T> a) { return f*Vec<N,T>(m) + a; }
SINT Vec<N,T> mad(Vec<N,T> f, Vec<N,T> m, T a) { return f*m + Vec<N,T>(a); }
SINT Vec<N,T> mad(Vec<N,T> f, T m, T a) { return f*Vec<N,T>(m) + Vec<N,T>(a); }
SINT Vec<N,T> mad(T f, Vec<N,T> m, T a) { return Vec<N,T>(f)*m + Vec<N,T>(a); }
SINT Vec<N,T> mad(T f, T m, Vec<N,T> a) { return Vec<N,T>(f)*Vec<N,T>(m) + a; }

// The various op= operators, for vectors...
SINT Vec<N,T>& operator+=(Vec<N,T>& x, Vec<N,T> y) { return (x = x + y); }
SINT Vec<N,T>& operator-=(Vec<N,T>& x, Vec<N,T> y) { return (x = x - y); }
SINT Vec<N,T>& operator*=(Vec<N,T>& x, Vec<N,T> y) { return (x = x * y); }
SINT Vec<N,T>& operator/=(Vec<N,T>& x, Vec<N,T> y) { return (x = x / y); }
SINT Vec<N,T>& operator^=(Vec<N,T>& x, Vec<N,T> y) { return (x = x ^ y); }
SINT Vec<N,T>& operator&=(Vec<N,T>& x, Vec<N,T> y) { return (x = x & y); }
SINT Vec<N,T>& operator|=(Vec<N,T>& x, Vec<N,T> y) { return (x = x | y); }

// ... for scalars...
SINT Vec<N,T>& operator+=(Vec<N,T>& x, T y) { return (x = x + Vec<N,T>(y)); }
SINT Vec<N,T>& operator-=(Vec<N,T>& x, T y) { return (x = x - Vec<N,T>(y)); }
SINT Vec<N,T>& operator*=(Vec<N,T>& x, T y) { return (x = x * Vec<N,T>(y)); }
SINT Vec<N,T>& operator/=(Vec<N,T>& x, T y) { return (x = x / Vec<N,T>(y)); }
SINT Vec<N,T>& operator^=(Vec<N,T>& x, T y) { return (x = x ^ Vec<N,T>(y)); }
SINT Vec<N,T>& operator&=(Vec<N,T>& x, T y) { return (x = x & Vec<N,T>(y)); }
SINT Vec<N,T>& operator|=(Vec<N,T>& x, T y) { return (x = x | Vec<N,T>(y)); }

// ... and for shifts.
SINT Vec<N,T>& operator<<=(Vec<N,T>& x, int bits) { return (x = x << bits); }
SINT Vec<N,T>& operator>>=(Vec<N,T>& x, int bits) { return (x = x >> bits); }

}  // namespace skvx

// These next few routines take extra template arguments that prevent
// argument-dependent lookup.  They must live outside the skvx namespace,
// but since they operate only on skvx::Vec, that shouldn't be a big deal.

// cast() Vec<N,S> to Vec<N,D>, as if applying a C-cast to each lane.
template <typename D, typename S>
static inline skvx::Vec<1,D> cast(skvx::Vec<1,S> src) { return (D)src.val; }

template <typename D, int N, typename S>
static inline skvx::Vec<N,D> cast(skvx::Vec<N,S> src) {
#if !defined(SKNX_NO_SIMD) && defined(__clang__)
    return skvx::to_vec(__builtin_convertvector(skvx::to_vext(src), skvx::VExt<N,D>));
#else
    return join(cast<D>(src.lo), cast<D>(src.hi));
#endif
}

// Shuffle values from a vector pretty arbitrarily:
//    skvx::Vec<4,float> rgba = {R,G,B,A};
//    shuffle<2,1,0,3>        (rgba) ~> {B,G,R,A}
//    shuffle<2,1>            (rgba) ~> {B,G}
//    shuffle<2,1,2,1,2,1,2,1>(rgba) ~> {B,G,B,G,B,G,B,G}
//    shuffle<3,3,3,3>        (rgba) ~> {A,A,A,A}
// The only real restriction is that the output also be a legal N=power-of-two sknx::Vec.
template <int... Ix, int N, typename T>
static inline skvx::Vec<sizeof...(Ix),T> shuffle(skvx::Vec<N,T> x) {
    return { x[Ix]... };
}

namespace skvx {

// Platform-specific specializations and overloads can now drop in here.

#if !defined(SKNX_NO_SIMD) && defined(__SSE__)
    static Vec<2,float>  sqrt(Vec<2,float> x) { return shuffle<0,1>( sqrt(shuffle<0,1,0,1>(x))); }
    static Vec<2,float> rsqrt(Vec<2,float> x) { return shuffle<0,1>(rsqrt(shuffle<0,1,0,1>(x))); }
    static Vec<2,float>   rcp(Vec<2,float> x) { return shuffle<0,1>(  rcp(shuffle<0,1,0,1>(x))); }

    static Vec<4,float> sqrt(Vec<4,float> x) {
        return bit_pun<Vec<4,float>>(_mm_sqrt_ps(bit_pun<__m128>(x)));
    }
    static Vec<4,float> rsqrt(Vec<4,float> x) {
        return bit_pun<Vec<4,float>>(_mm_rsqrt_ps(bit_pun<__m128>(x)));
    }
    static Vec<4,float> rcp(Vec<4,float> x) {
        return bit_pun<Vec<4,float>>(_mm_rcp_ps(bit_pun<__m128>(x)));
    }
#endif

}  // namespace skvx

#undef SINT
#undef SIT

#endif//SKVX_DEFINED