hwy/ops/scalar-inl.h

// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Single-element vectors and operations.
// External include guard in highway.h - see comment there.

#include <stddef.h>
#include <stdint.h>

#include "hwy/base.h"
#include "hwy/ops/shared-inl.h"

HWY_BEFORE_NAMESPACE();
namespace hwy {
namespace HWY_NAMESPACE {

// Single instruction, single data.
template <typename T>
using Sisd = Simd<T, 1, 0>;

// (Wrapper class required for overloading comparison operators.)
template <typename T>
struct Vec1 {
  HWY_INLINE Vec1() = default;
  Vec1(const Vec1&) = default;
  Vec1& operator=(const Vec1&) = default;
  HWY_INLINE explicit Vec1(const T t) : raw(t) {}

  HWY_INLINE Vec1& operator*=(const Vec1 other) {
    return *this = (*this * other);
  }
  HWY_INLINE Vec1& operator/=(const Vec1 other) {
    return *this = (*this / other);
  }
  HWY_INLINE Vec1& operator+=(const Vec1 other) {
    return *this = (*this + other);
  }
  HWY_INLINE Vec1& operator-=(const Vec1 other) {
    return *this = (*this - other);
  }
  HWY_INLINE Vec1& operator&=(const Vec1 other) {
    return *this = (*this & other);
  }
  HWY_INLINE Vec1& operator|=(const Vec1 other) {
    return *this = (*this | other);
  }
  HWY_INLINE Vec1& operator^=(const Vec1 other) {
    return *this = (*this ^ other);
  }

  T raw;
};

// 0 or FF..FF, same size as Vec1.
template <typename T>
class Mask1 {
  using Raw = hwy::MakeUnsigned<T>;

 public:
  static HWY_INLINE Mask1<T> FromBool(bool b) {
    Mask1<T> mask;
    mask.bits = b ? ~Raw(0) : 0;
    return mask;
  }

  Raw bits;
};

namespace detail {

// Deduce Sisd<T> from Vec1<T>
struct Deduce1 {
  template <typename T>
  Sisd<T> operator()(Vec1<T>) const {
    return Sisd<T>();
  }
};

}  // namespace detail

template <class V>
using DFromV = decltype(detail::Deduce1()(V()));

template <class V>
using TFromV = TFromD<DFromV<V>>;

// ------------------------------ BitCast

template <typename T, typename FromT>
HWY_API Vec1<T> BitCast(Sisd<T> /* tag */, Vec1<FromT> v) {
  static_assert(sizeof(T) <= sizeof(FromT), "Promoting is undefined");
  T to;
  CopyBytes<sizeof(FromT)>(&v.raw, &to);
  return Vec1<T>(to);
}

// ------------------------------ Set

template <typename T>
HWY_API Vec1<T> Zero(Sisd<T> /* tag */) {
  return Vec1<T>(T(0));
}

template <typename T, typename T2>
HWY_API Vec1<T> Set(Sisd<T> /* tag */, const T2 t) {
  return Vec1<T>(static_cast<T>(t));
}

template <typename T>
HWY_API Vec1<T> Undefined(Sisd<T> d) {
  return Zero(d);
}

template <typename T, typename T2>
HWY_API Vec1<T> Iota(const Sisd<T> /* tag */, const T2 first) {
  return Vec1<T>(static_cast<T>(first));
}

// ================================================== LOGICAL

// ------------------------------ Not

template <typename T>
HWY_API Vec1<T> Not(const Vec1<T> v) {
  using TU = MakeUnsigned<T>;
  const Sisd<TU> du;
  return BitCast(Sisd<T>(), Vec1<TU>(static_cast<TU>(~BitCast(du, v).raw)));
}

// ------------------------------ And

template <typename T>
HWY_API Vec1<T> And(const Vec1<T> a, const Vec1<T> b) {
  using TU = MakeUnsigned<T>;
  const Sisd<TU> du;
  return BitCast(Sisd<T>(), Vec1<TU>(BitCast(du, a).raw & BitCast(du, b).raw));
}
template <typename T>
HWY_API Vec1<T> operator&(const Vec1<T> a, const Vec1<T> b) {
  return And(a, b);
}

// ------------------------------ AndNot

template <typename T>
HWY_API Vec1<T> AndNot(const Vec1<T> a, const Vec1<T> b) {
  using TU = MakeUnsigned<T>;
  const Sisd<TU> du;
  return BitCast(Sisd<T>(), Vec1<TU>(static_cast<TU>(~BitCast(du, a).raw &
                                                     BitCast(du, b).raw)));
}

// ------------------------------ Or

template <typename T>
HWY_API Vec1<T> Or(const Vec1<T> a, const Vec1<T> b) {
  using TU = MakeUnsigned<T>;
  const Sisd<TU> du;
  return BitCast(Sisd<T>(), Vec1<TU>(BitCast(du, a).raw | BitCast(du, b).raw));
}
template <typename T>
HWY_API Vec1<T> operator|(const Vec1<T> a, const Vec1<T> b) {
  return Or(a, b);
}

// ------------------------------ Xor

template <typename T>
HWY_API Vec1<T> Xor(const Vec1<T> a, const Vec1<T> b) {
  using TU = MakeUnsigned<T>;
  const Sisd<TU> du;
  return BitCast(Sisd<T>(), Vec1<TU>(BitCast(du, a).raw ^ BitCast(du, b).raw));
}
template <typename T>
HWY_API Vec1<T> operator^(const Vec1<T> a, const Vec1<T> b) {
  return Xor(a, b);
}

// ------------------------------ OrAnd

template <typename T>
HWY_API Vec1<T> OrAnd(const Vec1<T> o, const Vec1<T> a1, const Vec1<T> a2) {
  return Or(o, And(a1, a2));
}

// ------------------------------ IfVecThenElse

template <typename T>
HWY_API Vec1<T> IfVecThenElse(Vec1<T> mask, Vec1<T> yes, Vec1<T> no) {
  return IfThenElse(MaskFromVec(mask), yes, no);
}

// ------------------------------ CopySign

template <typename T>
HWY_API Vec1<T> CopySign(const Vec1<T> magn, const Vec1<T> sign) {
  static_assert(IsFloat<T>(), "Only makes sense for floating-point");
  const auto msb = SignBit(Sisd<T>());
  return Or(AndNot(msb, magn), And(msb, sign));
}

template <typename T>
HWY_API Vec1<T> CopySignToAbs(const Vec1<T> abs, const Vec1<T> sign) {
  static_assert(IsFloat<T>(), "Only makes sense for floating-point");
  return Or(abs, And(SignBit(Sisd<T>()), sign));
}

// ------------------------------ BroadcastSignBit

template <typename T>
HWY_API Vec1<T> BroadcastSignBit(const Vec1<T> v) {
  // This is used inside ShiftRight, so we cannot implement in terms of it.
  return v.raw < 0 ? Vec1<T>(T(-1)) : Vec1<T>(0);
}

// ------------------------------ PopulationCount

#ifdef HWY_NATIVE_POPCNT
#undef HWY_NATIVE_POPCNT
#else
#define HWY_NATIVE_POPCNT
#endif

template <typename T>
HWY_API Vec1<T> PopulationCount(Vec1<T> v) {
  return Vec1<T>(static_cast<T>(PopCount(v.raw)));
}

// ------------------------------ Mask

template <typename TFrom, typename TTo>
HWY_API Mask1<TTo> RebindMask(Sisd<TTo> /*tag*/, Mask1<TFrom> m) {
  static_assert(sizeof(TFrom) == sizeof(TTo), "Must have same size");
  return Mask1<TTo>{m.bits};
}

// v must be 0 or FF..FF.
template <typename T>
HWY_API Mask1<T> MaskFromVec(const Vec1<T> v) {
  Mask1<T> mask;
  CopyBytes<sizeof(mask.bits)>(&v.raw, &mask.bits);
  return mask;
}

template <typename T>
Vec1<T> VecFromMask(const Mask1<T> mask) {
  Vec1<T> v;
  CopyBytes<sizeof(v.raw)>(&mask.bits, &v.raw);
  return v;
}

template <typename T>
Vec1<T> VecFromMask(Sisd<T> /* tag */, const Mask1<T> mask) {
  Vec1<T> v;
  CopyBytes<sizeof(v.raw)>(&mask.bits, &v.raw);
  return v;
}

template <typename T>
HWY_API Mask1<T> FirstN(Sisd<T> /*tag*/, size_t n) {
  return Mask1<T>::FromBool(n != 0);
}

// Returns mask ? yes : no.
template <typename T>
HWY_API Vec1<T> IfThenElse(const Mask1<T> mask, const Vec1<T> yes,
                           const Vec1<T> no) {
  return mask.bits ? yes : no;
}

template <typename T>
HWY_API Vec1<T> IfThenElseZero(const Mask1<T> mask, const Vec1<T> yes) {
  return mask.bits ? yes : Vec1<T>(0);
}

template <typename T>
HWY_API Vec1<T> IfThenZeroElse(const Mask1<T> mask, const Vec1<T> no) {
  return mask.bits ? Vec1<T>(0) : no;
}

template <typename T>
HWY_API Vec1<T> IfNegativeThenElse(Vec1<T> v, Vec1<T> yes, Vec1<T> no) {
  return v.raw < 0 ? yes : no;
}

template <typename T>
HWY_API Vec1<T> ZeroIfNegative(const Vec1<T> v) {
  return v.raw < 0 ? Vec1<T>(0) : v;
}

// ------------------------------ Mask logical

template <typename T>
HWY_API Mask1<T> Not(const Mask1<T> m) {
  return MaskFromVec(Not(VecFromMask(Sisd<T>(), m)));
}

template <typename T>
HWY_API Mask1<T> And(const Mask1<T> a, Mask1<T> b) {
  const Sisd<T> d;
  return MaskFromVec(And(VecFromMask(d, a), VecFromMask(d, b)));
}

template <typename T>
HWY_API Mask1<T> AndNot(const Mask1<T> a, Mask1<T> b) {
  const Sisd<T> d;
  return MaskFromVec(AndNot(VecFromMask(d, a), VecFromMask(d, b)));
}

template <typename T>
HWY_API Mask1<T> Or(const Mask1<T> a, Mask1<T> b) {
  const Sisd<T> d;
  return MaskFromVec(Or(VecFromMask(d, a), VecFromMask(d, b)));
}

template <typename T>
HWY_API Mask1<T> Xor(const Mask1<T> a, Mask1<T> b) {
  const Sisd<T> d;
  return MaskFromVec(Xor(VecFromMask(d, a), VecFromMask(d, b)));
}

// ================================================== SHIFTS

// ------------------------------ ShiftLeft/ShiftRight (BroadcastSignBit)

template <int kBits, typename T>
HWY_API Vec1<T> ShiftLeft(const Vec1<T> v) {
  static_assert(0 <= kBits && kBits < sizeof(T) * 8, "Invalid shift");
  return Vec1<T>(static_cast<hwy::MakeUnsigned<T>>(v.raw) << kBits);
}

template <int kBits, typename T>
HWY_API Vec1<T> ShiftRight(const Vec1<T> v) {
  static_assert(0 <= kBits && kBits < sizeof(T) * 8, "Invalid shift");
#if __cplusplus >= 202002L
  // Signed right shift is now guaranteed to be arithmetic (rounding toward
  // negative infinity, i.e. shifting in the sign bit).
  return Vec1<T>(v.raw >> kBits);
#else
  if (IsSigned<T>()) {
    // Emulate arithmetic shift using only logical (unsigned) shifts, because
    // signed shifts are still implementation-defined.
    using TU = hwy::MakeUnsigned<T>;
    const Sisd<TU> du;
    const TU shifted = BitCast(du, v).raw >> kBits;
    const TU sign = BitCast(du, BroadcastSignBit(v)).raw;
    const TU upper = sign << (sizeof(TU) * 8 - 1 - kBits);
    return BitCast(Sisd<T>(), Vec1<TU>(shifted | upper));
  } else {
    return Vec1<T>(v.raw >> kBits);  // unsigned, logical shift
  }
#endif
}

// ------------------------------ RotateRight (ShiftRight)

template <int kBits, typename T>
HWY_API Vec1<T> RotateRight(const Vec1<T> v) {
  static_assert(0 <= kBits && kBits < sizeof(T) * 8, "Invalid shift");
  if (kBits == 0) return v;
  return Or(ShiftRight<kBits>(v), ShiftLeft<sizeof(T) * 8 - kBits>(v));
}

// ------------------------------ ShiftLeftSame (BroadcastSignBit)

template <typename T>
HWY_API Vec1<T> ShiftLeftSame(const Vec1<T> v, int bits) {
  return Vec1<T>(static_cast<hwy::MakeUnsigned<T>>(v.raw) << bits);
}

template <typename T>
HWY_API Vec1<T> ShiftRightSame(const Vec1<T> v, int bits) {
#if __cplusplus >= 202002L
  // Signed right shift is now guaranteed to be arithmetic (rounding toward
  // negative infinity, i.e. shifting in the sign bit).
  return Vec1<T>(v.raw >> bits);
#else
  if (IsSigned<T>()) {
    // Emulate arithmetic shift using only logical (unsigned) shifts, because
    // signed shifts are still implementation-defined.
    using TU = hwy::MakeUnsigned<T>;
    const Sisd<TU> du;
    const TU shifted = BitCast(du, v).raw >> bits;
    const TU sign = BitCast(du, BroadcastSignBit(v)).raw;
    const TU upper = sign << (sizeof(TU) * 8 - 1 - bits);
    return BitCast(Sisd<T>(), Vec1<TU>(shifted | upper));
  } else {
    return Vec1<T>(v.raw >> bits);  // unsigned, logical shift
  }
#endif
}

// ------------------------------ Shl

// Single-lane => same as ShiftLeftSame except for the argument type.
template <typename T>
HWY_API Vec1<T> operator<<(const Vec1<T> v, const Vec1<T> bits) {
  return ShiftLeftSame(v, static_cast<int>(bits.raw));
}

template <typename T>
HWY_API Vec1<T> operator>>(const Vec1<T> v, const Vec1<T> bits) {
  return ShiftRightSame(v, static_cast<int>(bits.raw));
}

// ================================================== ARITHMETIC

template <typename T>
HWY_API Vec1<T> operator+(Vec1<T> a, Vec1<T> b) {
  const uint64_t a64 = static_cast<uint64_t>(a.raw);
  const uint64_t b64 = static_cast<uint64_t>(b.raw);
  return Vec1<T>(static_cast<T>((a64 + b64) & static_cast<uint64_t>(~T(0))));
}
HWY_API Vec1<float> operator+(const Vec1<float> a, const Vec1<float> b) {
  return Vec1<float>(a.raw + b.raw);
}
HWY_API Vec1<double> operator+(const Vec1<double> a, const Vec1<double> b) {
  return Vec1<double>(a.raw + b.raw);
}

template <typename T>
HWY_API Vec1<T> operator-(Vec1<T> a, Vec1<T> b) {
  const uint64_t a64 = static_cast<uint64_t>(a.raw);
  const uint64_t b64 = static_cast<uint64_t>(b.raw);
  return Vec1<T>(static_cast<T>((a64 - b64) & static_cast<uint64_t>(~T(0))));
}
HWY_API Vec1<float> operator-(const Vec1<float> a, const Vec1<float> b) {
  return Vec1<float>(a.raw - b.raw);
}
HWY_API Vec1<double> operator-(const Vec1<double> a, const Vec1<double> b) {
  return Vec1<double>(a.raw - b.raw);
}

// ------------------------------ SumsOf8

HWY_API Vec1<uint64_t> SumsOf8(const Vec1<uint8_t> v) {
  return Vec1<uint64_t>(v.raw);
}

// ------------------------------ SaturatedAdd

// Returns a + b clamped to the destination range.

// Unsigned
HWY_API Vec1<uint8_t> SaturatedAdd(const Vec1<uint8_t> a,
                                   const Vec1<uint8_t> b) {
  return Vec1<uint8_t>(
      static_cast<uint8_t>(HWY_MIN(HWY_MAX(0, a.raw + b.raw), 255)));
}
HWY_API Vec1<uint16_t> SaturatedAdd(const Vec1<uint16_t> a,
                                    const Vec1<uint16_t> b) {
  return Vec1<uint16_t>(
      static_cast<uint16_t>(HWY_MIN(HWY_MAX(0, a.raw + b.raw), 65535)));
}

// Signed
HWY_API Vec1<int8_t> SaturatedAdd(const Vec1<int8_t> a, const Vec1<int8_t> b) {
  return Vec1<int8_t>(
      static_cast<int8_t>(HWY_MIN(HWY_MAX(-128, a.raw + b.raw), 127)));
}
HWY_API Vec1<int16_t> SaturatedAdd(const Vec1<int16_t> a,
                                   const Vec1<int16_t> b) {
  return Vec1<int16_t>(
      static_cast<int16_t>(HWY_MIN(HWY_MAX(-32768, a.raw + b.raw), 32767)));
}

// ------------------------------ Saturating subtraction

// Returns a - b clamped to the destination range.

// Unsigned
HWY_API Vec1<uint8_t> SaturatedSub(const Vec1<uint8_t> a,
                                   const Vec1<uint8_t> b) {
  return Vec1<uint8_t>(
      static_cast<uint8_t>(HWY_MIN(HWY_MAX(0, a.raw - b.raw), 255)));
}
HWY_API Vec1<uint16_t> SaturatedSub(const Vec1<uint16_t> a,
                                    const Vec1<uint16_t> b) {
  return Vec1<uint16_t>(
      static_cast<uint16_t>(HWY_MIN(HWY_MAX(0, a.raw - b.raw), 65535)));
}

// Signed
HWY_API Vec1<int8_t> SaturatedSub(const Vec1<int8_t> a, const Vec1<int8_t> b) {
  return Vec1<int8_t>(
      static_cast<int8_t>(HWY_MIN(HWY_MAX(-128, a.raw - b.raw), 127)));
}
HWY_API Vec1<int16_t> SaturatedSub(const Vec1<int16_t> a,
                                   const Vec1<int16_t> b) {
  return Vec1<int16_t>(
      static_cast<int16_t>(HWY_MIN(HWY_MAX(-32768, a.raw - b.raw), 32767)));
}

// ------------------------------ Average

// Returns (a + b + 1) / 2

HWY_API Vec1<uint8_t> AverageRound(const Vec1<uint8_t> a,
                                   const Vec1<uint8_t> b) {
  return Vec1<uint8_t>(static_cast<uint8_t>((a.raw + b.raw + 1) / 2));
}
HWY_API Vec1<uint16_t> AverageRound(const Vec1<uint16_t> a,
                                    const Vec1<uint16_t> b) {
  return Vec1<uint16_t>(static_cast<uint16_t>((a.raw + b.raw + 1) / 2));
}

// ------------------------------ Absolute value

template <typename T>
HWY_API Vec1<T> Abs(const Vec1<T> a) {
  const T i = a.raw;
  return (i >= 0 || i == hwy::LimitsMin<T>()) ? a : Vec1<T>(-i);
}
HWY_API Vec1<float> Abs(const Vec1<float> a) {
  return Vec1<float>(std::abs(a.raw));
}
HWY_API Vec1<double> Abs(const Vec1<double> a) {
  return Vec1<double>(std::abs(a.raw));
}

// ------------------------------ min/max

template <typename T, HWY_IF_NOT_FLOAT(T)>
HWY_API Vec1<T> Min(const Vec1<T> a, const Vec1<T> b) {
  return Vec1<T>(HWY_MIN(a.raw, b.raw));
}

template <typename T, HWY_IF_FLOAT(T)>
HWY_API Vec1<T> Min(const Vec1<T> a, const Vec1<T> b) {
  if (std::isnan(a.raw)) return b;
  if (std::isnan(b.raw)) return a;
  return Vec1<T>(HWY_MIN(a.raw, b.raw));
}

template <typename T, HWY_IF_NOT_FLOAT(T)>
HWY_API Vec1<T> Max(const Vec1<T> a, const Vec1<T> b) {
  return Vec1<T>(HWY_MAX(a.raw, b.raw));
}

template <typename T, HWY_IF_FLOAT(T)>
HWY_API Vec1<T> Max(const Vec1<T> a, const Vec1<T> b) {
  if (std::isnan(a.raw)) return b;
  if (std::isnan(b.raw)) return a;
  return Vec1<T>(HWY_MAX(a.raw, b.raw));
}

// ------------------------------ Floating-point negate

template <typename T, HWY_IF_FLOAT(T)>
HWY_API Vec1<T> Neg(const Vec1<T> v) {
  return Xor(v, SignBit(Sisd<T>()));
}

template <typename T, HWY_IF_NOT_FLOAT(T)>
HWY_API Vec1<T> Neg(const Vec1<T> v) {
  return Zero(Sisd<T>()) - v;
}

// ------------------------------ mul/div

template <typename T, HWY_IF_FLOAT(T)>
HWY_API Vec1<T> operator*(const Vec1<T> a, const Vec1<T> b) {
  return Vec1<T>(static_cast<T>(double(a.raw) * b.raw));
}

template <typename T, HWY_IF_SIGNED(T)>
HWY_API Vec1<T> operator*(const Vec1<T> a, const Vec1<T> b) {
  return Vec1<T>(static_cast<T>(int64_t(a.raw) * b.raw));
}

template <typename T, HWY_IF_UNSIGNED(T)>
HWY_API Vec1<T> operator*(const Vec1<T> a, const Vec1<T> b) {
  return Vec1<T>(static_cast<T>(uint64_t(a.raw) * b.raw));
}

template <typename T>
HWY_API Vec1<T> operator/(const Vec1<T> a, const Vec1<T> b) {
  return Vec1<T>(a.raw / b.raw);
}

// Returns the upper 16 bits of a * b in each lane.
HWY_API Vec1<int16_t> MulHigh(const Vec1<int16_t> a, const Vec1<int16_t> b) {
  return Vec1<int16_t>(static_cast<int16_t>((a.raw * b.raw) >> 16));
}
HWY_API Vec1<uint16_t> MulHigh(const Vec1<uint16_t> a, const Vec1<uint16_t> b) {
  // Cast to uint32_t first to prevent overflow. Otherwise the result of
  // uint16_t * uint16_t is in "int" which may overflow. In practice the result
  // is the same but this way it is also defined.
  return Vec1<uint16_t>(static_cast<uint16_t>(
      (static_cast<uint32_t>(a.raw) * static_cast<uint32_t>(b.raw)) >> 16));
}

// Multiplies even lanes (0, 2 ..) and returns the double-wide result.
HWY_API Vec1<int64_t> MulEven(const Vec1<int32_t> a, const Vec1<int32_t> b) {
  const int64_t a64 = a.raw;
  return Vec1<int64_t>(a64 * b.raw);
}
HWY_API Vec1<uint64_t> MulEven(const Vec1<uint32_t> a, const Vec1<uint32_t> b) {
  const uint64_t a64 = a.raw;
  return Vec1<uint64_t>(a64 * b.raw);
}

// Approximate reciprocal
HWY_API Vec1<float> ApproximateReciprocal(const Vec1<float> v) {
  // Zero inputs are allowed, but callers are responsible for replacing the
  // return value with something else (typically using IfThenElse). This check
  // avoids a ubsan error. The return value is arbitrary.
  if (v.raw == 0.0f) return Vec1<float>(0.0f);
  return Vec1<float>(1.0f / v.raw);
}

// Absolute value of difference.
HWY_API Vec1<float> AbsDiff(const Vec1<float> a, const Vec1<float> b) {
  return Abs(a - b);
}

// ------------------------------ Floating-point multiply-add variants

template <typename T>
HWY_API Vec1<T> MulAdd(const Vec1<T> mul, const Vec1<T> x, const Vec1<T> add) {
  return mul * x + add;
}

template <typename T>
HWY_API Vec1<T> NegMulAdd(const Vec1<T> mul, const Vec1<T> x,
                          const Vec1<T> add) {
  return add - mul * x;
}

template <typename T>
HWY_API Vec1<T> MulSub(const Vec1<T> mul, const Vec1<T> x, const Vec1<T> sub) {
  return mul * x - sub;
}

template <typename T>
HWY_API Vec1<T> NegMulSub(const Vec1<T> mul, const Vec1<T> x,
                          const Vec1<T> sub) {
  return Neg(mul) * x - sub;
}

// ------------------------------ Floating-point square root

// Approximate reciprocal square root
HWY_API Vec1<float> ApproximateReciprocalSqrt(const Vec1<float> v) {
  float f = v.raw;
  const float half = f * 0.5f;
  uint32_t bits;
  CopyBytes<4>(&f, &bits);
  // Initial guess based on log2(f)
  bits = 0x5F3759DF - (bits >> 1);
  CopyBytes<4>(&bits, &f);
  // One Newton-Raphson iteration
  return Vec1<float>(f * (1.5f - (half * f * f)));
}

// Square root
HWY_API Vec1<float> Sqrt(const Vec1<float> v) {
  return Vec1<float>(std::sqrt(v.raw));
}
HWY_API Vec1<double> Sqrt(const Vec1<double> v) {
  return Vec1<double>(std::sqrt(v.raw));
}

// ------------------------------ Floating-point rounding

template <typename T>
HWY_API Vec1<T> Round(const Vec1<T> v) {
  using TI = MakeSigned<T>;
  if (!(Abs(v).raw < MantissaEnd<T>())) {  // Huge or NaN
    return v;
  }
  const T bias = v.raw < T(0.0) ? T(-0.5) : T(0.5);
  const TI rounded = static_cast<TI>(v.raw + bias);
  if (rounded == 0) return CopySignToAbs(Vec1<T>(0), v);
  // Round to even
  if ((rounded & 1) && std::abs(rounded - v.raw) == T(0.5)) {
    return Vec1<T>(static_cast<T>(rounded - (v.raw < T(0) ? -1 : 1)));
  }
  return Vec1<T>(static_cast<T>(rounded));
}

// Round-to-nearest even.
HWY_API Vec1<int32_t> NearestInt(const Vec1<float> v) {
  using T = float;
  using TI = int32_t;

  const T abs = Abs(v).raw;
  const bool signbit = std::signbit(v.raw);

  if (!(abs < MantissaEnd<T>())) {  // Huge or NaN
    // Check if too large to cast or NaN
    if (!(abs <= static_cast<T>(LimitsMax<TI>()))) {
      return Vec1<TI>(signbit ? LimitsMin<TI>() : LimitsMax<TI>());
    }
    return Vec1<int32_t>(static_cast<TI>(v.raw));
  }
  const T bias = v.raw < T(0.0) ? T(-0.5) : T(0.5);
  const TI rounded = static_cast<TI>(v.raw + bias);
  if (rounded == 0) return Vec1<int32_t>(0);
  // Round to even
  if ((rounded & 1) && std::abs(static_cast<T>(rounded) - v.raw) == T(0.5)) {
    return Vec1<TI>(rounded - (signbit ? -1 : 1));
  }
  return Vec1<TI>(rounded);
}

template <typename T>
HWY_API Vec1<T> Trunc(const Vec1<T> v) {
  using TI = MakeSigned<T>;
  if (!(Abs(v).raw <= MantissaEnd<T>())) {  // Huge or NaN
    return v;
  }
  const TI truncated = static_cast<TI>(v.raw);
  if (truncated == 0) return CopySignToAbs(Vec1<T>(0), v);
  return Vec1<T>(static_cast<T>(truncated));
}

template <typename Float, typename Bits, int kMantissaBits, int kExponentBits,
          class V>
V Ceiling(const V v) {
  const Bits kExponentMask = (1ull << kExponentBits) - 1;
  const Bits kMantissaMask = (1ull << kMantissaBits) - 1;
  const Bits kBias = kExponentMask / 2;

  Float f = v.raw;
  const bool positive = f > Float(0.0);

  Bits bits;
  CopyBytes<sizeof(Bits)>(&v, &bits);

  const int exponent =
      static_cast<int>(((bits >> kMantissaBits) & kExponentMask) - kBias);
  // Already an integer.
  if (exponent >= kMantissaBits) return v;
  // |v| <= 1 => 0 or 1.
  if (exponent < 0) return positive ? V(1) : V(-0.0);

  const Bits mantissa_mask = kMantissaMask >> exponent;
  // Already an integer
  if ((bits & mantissa_mask) == 0) return v;

  // Clear fractional bits and round up
  if (positive) bits += (kMantissaMask + 1) >> exponent;
  bits &= ~mantissa_mask;

  CopyBytes<sizeof(Bits)>(&bits, &f);
  return V(f);
}

template <typename Float, typename Bits, int kMantissaBits, int kExponentBits,
          class V>
V Floor(const V v) {
  const Bits kExponentMask = (1ull << kExponentBits) - 1;
  const Bits kMantissaMask = (1ull << kMantissaBits) - 1;
  const Bits kBias = kExponentMask / 2;

  Float f = v.raw;
  const bool negative = f < Float(0.0);

  Bits bits;
  CopyBytes<sizeof(Bits)>(&v, &bits);

  const int exponent =
      static_cast<int>(((bits >> kMantissaBits) & kExponentMask) - kBias);
  // Already an integer.
  if (exponent >= kMantissaBits) return v;
  // |v| <= 1 => -1 or 0.
  if (exponent < 0) return V(negative ? Float(-1.0) : Float(0.0));

  const Bits mantissa_mask = kMantissaMask >> exponent;
  // Already an integer
  if ((bits & mantissa_mask) == 0) return v;

  // Clear fractional bits and round down
  if (negative) bits += (kMantissaMask + 1) >> exponent;
  bits &= ~mantissa_mask;

  CopyBytes<sizeof(Bits)>(&bits, &f);
  return V(f);
}

// Toward +infinity, aka ceiling
HWY_API Vec1<float> Ceil(const Vec1<float> v) {
  return Ceiling<float, uint32_t, 23, 8>(v);
}
HWY_API Vec1<double> Ceil(const Vec1<double> v) {
  return Ceiling<double, uint64_t, 52, 11>(v);
}

// Toward -infinity, aka floor
HWY_API Vec1<float> Floor(const Vec1<float> v) {
  return Floor<float, uint32_t, 23, 8>(v);
}
HWY_API Vec1<double> Floor(const Vec1<double> v) {
  return Floor<double, uint64_t, 52, 11>(v);
}

// ================================================== COMPARE

template <typename T>
HWY_API Mask1<T> operator==(const Vec1<T> a, const Vec1<T> b) {
  return Mask1<T>::FromBool(a.raw == b.raw);
}

template <typename T>
HWY_API Mask1<T> operator!=(const Vec1<T> a, const Vec1<T> b) {
  return Mask1<T>::FromBool(a.raw != b.raw);
}

template <typename T>
HWY_API Mask1<T> TestBit(const Vec1<T> v, const Vec1<T> bit) {
  static_assert(!hwy::IsFloat<T>(), "Only integer vectors supported");
  return (v & bit) == bit;
}

template <typename T>
HWY_API Mask1<T> operator<(const Vec1<T> a, const Vec1<T> b) {
  return Mask1<T>::FromBool(a.raw < b.raw);
}
template <typename T>
HWY_API Mask1<T> operator>(const Vec1<T> a, const Vec1<T> b) {
  return Mask1<T>::FromBool(a.raw > b.raw);
}

template <typename T>
HWY_API Mask1<T> operator<=(const Vec1<T> a, const Vec1<T> b) {
  return Mask1<T>::FromBool(a.raw <= b.raw);
}
template <typename T>
HWY_API Mask1<T> operator>=(const Vec1<T> a, const Vec1<T> b) {
  return Mask1<T>::FromBool(a.raw >= b.raw);
}

// ================================================== MEMORY

// ------------------------------ Load

template <typename T>
HWY_API Vec1<T> Load(Sisd<T> /* tag */, const T* HWY_RESTRICT aligned) {
  T t;
  CopyBytes<sizeof(T)>(aligned, &t);
  return Vec1<T>(t);
}

template <typename T>
HWY_API Vec1<T> MaskedLoad(Mask1<T> m, Sisd<T> d,
                           const T* HWY_RESTRICT aligned) {
  return IfThenElseZero(m, Load(d, aligned));
}

template <typename T>
HWY_API Vec1<T> LoadU(Sisd<T> d, const T* HWY_RESTRICT p) {
  return Load(d, p);
}

// In some use cases, "load single lane" is sufficient; otherwise avoid this.
template <typename T>
HWY_API Vec1<T> LoadDup128(Sisd<T> d, const T* HWY_RESTRICT aligned) {
  return Load(d, aligned);
}

// ------------------------------ Store

template <typename T>
HWY_API void Store(const Vec1<T> v, Sisd<T> /* tag */,
                   T* HWY_RESTRICT aligned) {
  CopyBytes<sizeof(T)>(&v.raw, aligned);
}

template <typename T>
HWY_API void StoreU(const Vec1<T> v, Sisd<T> d, T* HWY_RESTRICT p) {
  return Store(v, d, p);
}

// ------------------------------ StoreInterleaved3

HWY_API void StoreInterleaved3(const Vec1<uint8_t> v0, const Vec1<uint8_t> v1,
                               const Vec1<uint8_t> v2, Sisd<uint8_t> d,
                               uint8_t* HWY_RESTRICT unaligned) {
  StoreU(v0, d, unaligned + 0);
  StoreU(v1, d, unaligned + 1);
  StoreU(v2, d, unaligned + 2);
}

HWY_API void StoreInterleaved4(const Vec1<uint8_t> v0, const Vec1<uint8_t> v1,
                               const Vec1<uint8_t> v2, const Vec1<uint8_t> v3,
                               Sisd<uint8_t> d,
                               uint8_t* HWY_RESTRICT unaligned) {
  StoreU(v0, d, unaligned + 0);
  StoreU(v1, d, unaligned + 1);
  StoreU(v2, d, unaligned + 2);
  StoreU(v3, d, unaligned + 3);
}

// ------------------------------ Stream

template <typename T>
HWY_API void Stream(const Vec1<T> v, Sisd<T> d, T* HWY_RESTRICT aligned) {
  return Store(v, d, aligned);
}

// ------------------------------ Scatter

template <typename T, typename Offset>
HWY_API void ScatterOffset(Vec1<T> v, Sisd<T> d, T* base,
                           const Vec1<Offset> offset) {
  static_assert(sizeof(T) == sizeof(Offset), "Must match for portability");
  uint8_t* const base8 = reinterpret_cast<uint8_t*>(base) + offset.raw;
  return Store(v, d, reinterpret_cast<T*>(base8));
}

template <typename T, typename Index>
HWY_API void ScatterIndex(Vec1<T> v, Sisd<T> d, T* HWY_RESTRICT base,
                          const Vec1<Index> index) {
  static_assert(sizeof(T) == sizeof(Index), "Must match for portability");
  return Store(v, d, base + index.raw);
}

// ------------------------------ Gather

template <typename T, typename Offset>
HWY_API Vec1<T> GatherOffset(Sisd<T> d, const T* base,
                             const Vec1<Offset> offset) {
  static_assert(sizeof(T) == sizeof(Offset), "Must match for portability");
  const uintptr_t addr = reinterpret_cast<uintptr_t>(base) + offset.raw;
  return Load(d, reinterpret_cast<const T*>(addr));
}

template <typename T, typename Index>
HWY_API Vec1<T> GatherIndex(Sisd<T> d, const T* HWY_RESTRICT base,
                            const Vec1<Index> index) {
  static_assert(sizeof(T) == sizeof(Index), "Must match for portability");
  return Load(d, base + index.raw);
}

// ================================================== CONVERT

// ConvertTo and DemoteTo with floating-point input and integer output truncate
// (rounding toward zero).

template <typename FromT, typename ToT>
HWY_API Vec1<ToT> PromoteTo(Sisd<ToT> /* tag */, Vec1<FromT> from) {
  static_assert(sizeof(ToT) > sizeof(FromT), "Not promoting");
  // For bits Y > X, floatX->floatY and intX->intY are always representable.
  return Vec1<ToT>(static_cast<ToT>(from.raw));
}

// MSVC 19.10 cannot deduce the argument type if HWY_IF_FLOAT(FromT) is here,
// so we overload for FromT=double and ToT={float,int32_t}.
HWY_API Vec1<float> DemoteTo(Sisd<float> /* tag */, Vec1<double> from) {
  // Prevent ubsan errors when converting float to narrower integer/float
  if (std::isinf(from.raw) ||
      std::fabs(from.raw) > static_cast<double>(HighestValue<float>())) {
    return Vec1<float>(std::signbit(from.raw) ? LowestValue<float>()
                                              : HighestValue<float>());
  }
  return Vec1<float>(static_cast<float>(from.raw));
}
HWY_API Vec1<int32_t> DemoteTo(Sisd<int32_t> /* tag */, Vec1<double> from) {
  // Prevent ubsan errors when converting int32_t to narrower integer/int32_t
  if (std::isinf(from.raw) ||
      std::fabs(from.raw) > static_cast<double>(HighestValue<int32_t>())) {
    return Vec1<int32_t>(std::signbit(from.raw) ? LowestValue<int32_t>()
                                                : HighestValue<int32_t>());
  }
  return Vec1<int32_t>(static_cast<int32_t>(from.raw));
}

template <typename FromT, typename ToT>
HWY_API Vec1<ToT> DemoteTo(Sisd<ToT> /* tag */, Vec1<FromT> from) {
  static_assert(!IsFloat<FromT>(), "FromT=double are handled above");
  static_assert(sizeof(ToT) < sizeof(FromT), "Not demoting");

  // Int to int: choose closest value in ToT to `from` (avoids UB)
  from.raw = HWY_MIN(HWY_MAX(LimitsMin<ToT>(), from.raw), LimitsMax<ToT>());
  return Vec1<ToT>(static_cast<ToT>(from.raw));
}

HWY_API Vec1<float> PromoteTo(Sisd<float> /* tag */, const Vec1<float16_t> v) {
#if HWY_NATIVE_FLOAT16
  uint16_t bits16;
  CopyBytes<2>(&v.raw, &bits16);
#else
  const uint16_t bits16 = v.raw.bits;
#endif
  const uint32_t sign = static_cast<uint32_t>(bits16 >> 15);
  const uint32_t biased_exp = (bits16 >> 10) & 0x1F;
  const uint32_t mantissa = bits16 & 0x3FF;

  // Subnormal or zero
  if (biased_exp == 0) {
    const float subnormal =
        (1.0f / 16384) * (static_cast<float>(mantissa) * (1.0f / 1024));
    return Vec1<float>(sign ? -subnormal : subnormal);
  }

  // Normalized: convert the representation directly (faster than ldexp/tables).
  const uint32_t biased_exp32 = biased_exp + (127 - 15);
  const uint32_t mantissa32 = mantissa << (23 - 10);
  const uint32_t bits32 = (sign << 31) | (biased_exp32 << 23) | mantissa32;
  float out;
  CopyBytes<4>(&bits32, &out);
  return Vec1<float>(out);
}

HWY_API Vec1<float> PromoteTo(Sisd<float> d, const Vec1<bfloat16_t> v) {
  return Set(d, F32FromBF16(v.raw));
}

HWY_API Vec1<float16_t> DemoteTo(Sisd<float16_t> /* tag */,
                                 const Vec1<float> v) {
  uint32_t bits32;
  CopyBytes<4>(&v.raw, &bits32);
  const uint32_t sign = bits32 >> 31;
  const uint32_t biased_exp32 = (bits32 >> 23) & 0xFF;
  const uint32_t mantissa32 = bits32 & 0x7FFFFF;

  const int32_t exp = HWY_MIN(static_cast<int32_t>(biased_exp32) - 127, 15);

  // Tiny or zero => zero.
  Vec1<float16_t> out;
  if (exp < -24) {
#if HWY_NATIVE_FLOAT16
    const uint16_t zero = 0;
    CopyBytes<2>(&zero, &out.raw);
#else
    out.raw.bits = 0;
#endif
    return out;
  }

  uint32_t biased_exp16, mantissa16;

  // exp = [-24, -15] => subnormal
  if (exp < -14) {
    biased_exp16 = 0;
    const uint32_t sub_exp = static_cast<uint32_t>(-14 - exp);
    HWY_DASSERT(1 <= sub_exp && sub_exp < 11);
    mantissa16 = static_cast<uint32_t>((1u << (10 - sub_exp)) +
                                       (mantissa32 >> (13 + sub_exp)));
  } else {
    // exp = [-14, 15]
    biased_exp16 = static_cast<uint32_t>(exp + 15);
    HWY_DASSERT(1 <= biased_exp16 && biased_exp16 < 31);
    mantissa16 = mantissa32 >> 13;
  }

  HWY_DASSERT(mantissa16 < 1024);
  const uint32_t bits16 = (sign << 15) | (biased_exp16 << 10) | mantissa16;
  HWY_DASSERT(bits16 < 0x10000);
#if HWY_NATIVE_FLOAT16
  const uint16_t narrowed = static_cast<uint16_t>(bits16);  // big-endian safe
  CopyBytes<2>(&narrowed, &out.raw);
#else
  out.raw.bits = static_cast<uint16_t>(bits16);
#endif
  return out;
}

HWY_API Vec1<bfloat16_t> DemoteTo(Sisd<bfloat16_t> d, const Vec1<float> v) {
  return Set(d, BF16FromF32(v.raw));
}

template <typename FromT, typename ToT, HWY_IF_FLOAT(FromT)>
HWY_API Vec1<ToT> ConvertTo(Sisd<ToT> /* tag */, Vec1<FromT> from) {
  static_assert(sizeof(ToT) == sizeof(FromT), "Should have same size");
  // float## -> int##: return closest representable value. We cannot exactly
  // represent LimitsMax<ToT> in FromT, so use double.
  const double f = static_cast<double>(from.raw);
  if (std::isinf(from.raw) ||
      std::fabs(f) > static_cast<double>(LimitsMax<ToT>())) {
    return Vec1<ToT>(std::signbit(from.raw) ? LimitsMin<ToT>()
                                            : LimitsMax<ToT>());
  }
  return Vec1<ToT>(static_cast<ToT>(from.raw));
}

template <typename FromT, typename ToT, HWY_IF_NOT_FLOAT(FromT)>
HWY_API Vec1<ToT> ConvertTo(Sisd<ToT> /* tag */, Vec1<FromT> from) {
  static_assert(sizeof(ToT) == sizeof(FromT), "Should have same size");
  // int## -> float##: no check needed
  return Vec1<ToT>(static_cast<ToT>(from.raw));
}

HWY_API Vec1<uint8_t> U8FromU32(const Vec1<uint32_t> v) {
  return DemoteTo(Sisd<uint8_t>(), v);
}

// ================================================== COMBINE
// UpperHalf, ZeroExtendVector, Combine, Concat* are unsupported.

template <typename T>
HWY_API Vec1<T> LowerHalf(Vec1<T> v) {
  return v;
}

template <typename T>
HWY_API Vec1<T> LowerHalf(Sisd<T> /* tag */, Vec1<T> v) {
  return v;
}

// ================================================== SWIZZLE

template <typename T>
HWY_API T GetLane(const Vec1<T> v) {
  return v.raw;
}

template <typename T>
HWY_API Vec1<T> DupEven(Vec1<T> v) {
  return v;
}
// DupOdd is unsupported.

template <typename T>
HWY_API Vec1<T> OddEven(Vec1<T> /* odd */, Vec1<T> even) {
  return even;
}

template <typename T>
HWY_API Vec1<T> OddEvenBlocks(Vec1<T> /* odd */, Vec1<T> even) {
  return even;
}

// ------------------------------ SwapAdjacentBlocks

template <typename T>
HWY_API Vec1<T> SwapAdjacentBlocks(Vec1<T> v) {
  return v;
}

// ------------------------------ TableLookupLanes

// Returned by SetTableIndices for use by TableLookupLanes.
template <typename T>
struct Indices1 {
  MakeSigned<T> raw;
};

template <typename T, typename TI>
HWY_API Indices1<T> IndicesFromVec(Sisd<T>, Vec1<TI> vec) {
  static_assert(sizeof(T) == sizeof(TI), "Index size must match lane size");
  HWY_DASSERT(vec.raw == 0);
  return Indices1<T>{vec.raw};
}

template <typename T, typename TI>
HWY_API Indices1<T> SetTableIndices(Sisd<T> d, const TI* idx) {
  return IndicesFromVec(d, LoadU(idx));
}

template <typename T>
HWY_API Vec1<T> TableLookupLanes(const Vec1<T> v, const Indices1<T> /* idx */) {
  return v;
}

// ------------------------------ ReverseBlocks

// Single block: no change
template <typename T>
HWY_API Vec1<T> ReverseBlocks(Sisd<T> /* tag */, const Vec1<T> v) {
  return v;
}

// ------------------------------ Reverse

template <typename T>
HWY_API Vec1<T> Reverse(Sisd<T> /* tag */, const Vec1<T> v) {
  return v;
}

template <typename T>
HWY_API Vec1<T> Reverse2(Sisd<T> /* tag */, const Vec1<T> v) {
  return v;
}

template <typename T>
HWY_API Vec1<T> Reverse4(Sisd<T> /* tag */, const Vec1<T> v) {
  return v;
}

template <typename T>
HWY_API Vec1<T> Reverse8(Sisd<T> /* tag */, const Vec1<T> v) {
  return v;
}

// ================================================== BLOCKWISE
// Shift*Bytes, CombineShiftRightBytes, Interleave*, Shuffle* are unsupported.

// ------------------------------ Broadcast/splat any lane

template <int kLane, typename T>
HWY_API Vec1<T> Broadcast(const Vec1<T> v) {
  static_assert(kLane == 0, "Scalar only has one lane");
  return v;
}

// ------------------------------ TableLookupBytes, TableLookupBytesOr0

template <typename T, typename TI>
HWY_API Vec1<TI> TableLookupBytes(const Vec1<T> in, const Vec1<TI> indices) {
  uint8_t in_bytes[sizeof(T)];
  uint8_t idx_bytes[sizeof(T)];
  uint8_t out_bytes[sizeof(T)];
  CopyBytes<sizeof(T)>(&in, &in_bytes);
  CopyBytes<sizeof(T)>(&indices, &idx_bytes);
  for (size_t i = 0; i < sizeof(T); ++i) {
    out_bytes[i] = in_bytes[idx_bytes[i]];
  }
  TI out;
  CopyBytes<sizeof(TI)>(&out_bytes, &out);
  return Vec1<TI>{out};
}

template <typename T, typename TI>
HWY_API Vec1<TI> TableLookupBytesOr0(const Vec1<T> in, const Vec1<TI> indices) {
  uint8_t in_bytes[sizeof(T)];
  uint8_t idx_bytes[sizeof(T)];
  uint8_t out_bytes[sizeof(T)];
  CopyBytes<sizeof(T)>(&in, &in_bytes);
  CopyBytes<sizeof(T)>(&indices, &idx_bytes);
  for (size_t i = 0; i < sizeof(T); ++i) {
    out_bytes[i] = idx_bytes[i] & 0x80 ? 0 : in_bytes[idx_bytes[i]];
  }
  TI out;
  CopyBytes<sizeof(TI)>(&out_bytes, &out);
  return Vec1<TI>{out};
}

// ------------------------------ ZipLower

HWY_API Vec1<uint16_t> ZipLower(const Vec1<uint8_t> a, const Vec1<uint8_t> b) {
  return Vec1<uint16_t>(static_cast<uint16_t>((uint32_t(b.raw) << 8) + a.raw));
}
HWY_API Vec1<uint32_t> ZipLower(const Vec1<uint16_t> a,
                                const Vec1<uint16_t> b) {
  return Vec1<uint32_t>((uint32_t(b.raw) << 16) + a.raw);
}
HWY_API Vec1<uint64_t> ZipLower(const Vec1<uint32_t> a,
                                const Vec1<uint32_t> b) {
  return Vec1<uint64_t>((uint64_t(b.raw) << 32) + a.raw);
}
HWY_API Vec1<int16_t> ZipLower(const Vec1<int8_t> a, const Vec1<int8_t> b) {
  return Vec1<int16_t>(static_cast<int16_t>((int32_t(b.raw) << 8) + a.raw));
}
HWY_API Vec1<int32_t> ZipLower(const Vec1<int16_t> a, const Vec1<int16_t> b) {
  return Vec1<int32_t>((int32_t(b.raw) << 16) + a.raw);
}
HWY_API Vec1<int64_t> ZipLower(const Vec1<int32_t> a, const Vec1<int32_t> b) {
  return Vec1<int64_t>((int64_t(b.raw) << 32) + a.raw);
}

template <typename T, typename TW = MakeWide<T>, class VW = Vec1<TW>>
HWY_API VW ZipLower(Sisd<TW> /* tag */, Vec1<T> a, Vec1<T> b) {
  return VW(static_cast<TW>((TW{b.raw} << (sizeof(T) * 8)) + a.raw));
}

// ================================================== MASK

template <typename T>
HWY_API bool AllFalse(Sisd<T> /* tag */, const Mask1<T> mask) {
  return mask.bits == 0;
}

template <typename T>
HWY_API bool AllTrue(Sisd<T> /* tag */, const Mask1<T> mask) {
  return mask.bits != 0;
}

// `p` points to at least 8 readable bytes, not all of which need be valid.
template <typename T>
HWY_API Mask1<T> LoadMaskBits(Sisd<T> /* tag */,
                              const uint8_t* HWY_RESTRICT bits) {
  return Mask1<T>::FromBool((bits[0] & 1) != 0);
}

// `p` points to at least 8 writable bytes.
template <typename T>
HWY_API size_t StoreMaskBits(Sisd<T> d, const Mask1<T> mask, uint8_t* bits) {
  *bits = AllTrue(d, mask);
  return 1;
}

template <typename T>
HWY_API size_t CountTrue(Sisd<T> /* tag */, const Mask1<T> mask) {
  return mask.bits == 0 ? 0 : 1;
}

template <typename T>
HWY_API intptr_t FindFirstTrue(Sisd<T> /* tag */, const Mask1<T> mask) {
  return mask.bits == 0 ? -1 : 0;
}

// ------------------------------ Compress, CompressBits

template <typename T>
HWY_API Vec1<T> Compress(Vec1<T> v, const Mask1<T> /* mask */) {
  // Upper lanes are undefined, so result is the same independent of mask.
  return v;
}

template <typename T>
HWY_API Vec1<T> Compress(Vec1<T> v, const uint8_t* HWY_RESTRICT /* bits */) {
  return v;
}

// ------------------------------ CompressStore

template <typename T>
HWY_API size_t CompressStore(Vec1<T> v, const Mask1<T> mask, Sisd<T> d,
                             T* HWY_RESTRICT unaligned) {
  StoreU(Compress(v, mask), d, unaligned);
  return CountTrue(d, mask);
}

// ------------------------------ CompressBlendedStore

template <typename T>
HWY_API size_t CompressBlendedStore(Vec1<T> v, const Mask1<T> mask, Sisd<T> d,
                                    T* HWY_RESTRICT unaligned) {
  if (!mask.bits) return 0;
  StoreU(v, d, unaligned);
  return 1;
}

// ------------------------------ CompressBitsStore

template <typename T>
HWY_API size_t CompressBitsStore(Vec1<T> v, const uint8_t* HWY_RESTRICT bits,
                                 Sisd<T> d, T* HWY_RESTRICT unaligned) {
  const Mask1<T> mask = LoadMaskBits(d, bits);
  StoreU(Compress(v, mask), d, unaligned);
  return CountTrue(d, mask);
}

// ------------------------------ ReorderWidenMulAccumulate (MulAdd, ZipLower)

HWY_API Vec1<float> ReorderWidenMulAccumulate(Sisd<float> /* tag */,
                                              Vec1<bfloat16_t> a,
                                              Vec1<bfloat16_t> b,
                                              const Vec1<float> sum0,
                                              Vec1<float>& /* sum1 */) {
  return MulAdd(Vec1<float>(F32FromBF16(a.raw)),
                Vec1<float>(F32FromBF16(b.raw)), sum0);
}

// ================================================== REDUCTIONS

// Sum of all lanes, i.e. the only one.
template <typename T>
HWY_API Vec1<T> SumOfLanes(Sisd<T> /* tag */, const Vec1<T> v) {
  return v;
}
template <typename T>
HWY_API Vec1<T> MinOfLanes(Sisd<T> /* tag */, const Vec1<T> v) {
  return v;
}
template <typename T>
HWY_API Vec1<T> MaxOfLanes(Sisd<T> /* tag */, const Vec1<T> v) {
  return v;
}

// ================================================== Operator wrapper

template <class V>
HWY_API V Add(V a, V b) {
  return a + b;
}
template <class V>
HWY_API V Sub(V a, V b) {
  return a - b;
}

template <class V>
HWY_API V Mul(V a, V b) {
  return a * b;
}
template <class V>
HWY_API V Div(V a, V b) {
  return a / b;
}

template <class V>
V Shl(V a, V b) {
  return a << b;
}
template <class V>
V Shr(V a, V b) {
  return a >> b;
}

template <class V>
HWY_API auto Eq(V a, V b) -> decltype(a == b) {
  return a == b;
}
template <class V>
HWY_API auto Ne(V a, V b) -> decltype(a == b) {
  return a != b;
}
template <class V>
HWY_API auto Lt(V a, V b) -> decltype(a == b) {
  return a < b;
}

template <class V>
HWY_API auto Gt(V a, V b) -> decltype(a == b) {
  return a > b;
}
template <class V>
HWY_API auto Ge(V a, V b) -> decltype(a == b) {
  return a >= b;
}

template <class V>
HWY_API auto Le(V a, V b) -> decltype(a == b) {
  return a <= b;
}

// NOLINTNEXTLINE(google-readability-namespace-comments)
}  // namespace HWY_NAMESPACE
}  // namespace hwy
HWY_AFTER_NAMESPACE();