Make sure frexp() returns correct for argument 0.0

[gromacs.git] / src / gromacs / simd / impl_x86_mic / impl_x86_mic_simd_float.h

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#ifndef GMX_SIMD_IMPL_X86_MIC_SIMD_FLOAT_H
#define GMX_SIMD_IMPL_X86_MIC_SIMD_FLOAT_H

#include "config.h"

#include <cassert>
#include <cstdint>

#include <immintrin.h>

#include "gromacs/math/utilities.h"

namespace gmx
{

class SimdFloat
{
public:
    SimdFloat() {}

    SimdFloat(float f) : simdInternal_(_mm512_set1_ps(f)) {}

    // Internal utility constructor to simplify return statements
    SimdFloat(__m512 simd) : simdInternal_(simd) {}

    __m512 simdInternal_;
};

class SimdFInt32
{
public:
    SimdFInt32() {}

    SimdFInt32(std::int32_t i) : simdInternal_(_mm512_set1_epi32(i)) {}

    // Internal utility constructor to simplify return statements
    SimdFInt32(__m512i simd) : simdInternal_(simd) {}

    __m512i simdInternal_;
};

class SimdFBool
{
public:
    SimdFBool() {}

    SimdFBool(bool b) : simdInternal_(_mm512_int2mask(b ? 0xFFFF : 0)) {}

    // Internal utility constructor to simplify return statements
    SimdFBool(__mmask16 simd) : simdInternal_(simd) {}

    __mmask16 simdInternal_;
};

class SimdFIBool
{
public:
    SimdFIBool() {}

    SimdFIBool(bool b) : simdInternal_(_mm512_int2mask(b ? 0xFFFF : 0)) {}

    // Internal utility constructor to simplify return statements
    SimdFIBool(__mmask16 simd) : simdInternal_(simd) {}

    __mmask16 simdInternal_;
};

static inline SimdFloat gmx_simdcall simdLoad(const float* m, SimdFloatTag = {})
{
    assert(std::size_t(m) % 64 == 0);
    return { _mm512_load_ps(m) };
}

static inline void gmx_simdcall store(float* m, SimdFloat a)
{
    assert(std::size_t(m) % 64 == 0);
    _mm512_store_ps(m, a.simdInternal_);
}

static inline SimdFloat gmx_simdcall simdLoadU(const float* m, SimdFloatTag = {})
{
    return { _mm512_loadunpackhi_ps(_mm512_loadunpacklo_ps(_mm512_undefined_ps(), m), m + 16) };
}

static inline void gmx_simdcall storeU(float* m, SimdFloat a)
{
    _mm512_packstorelo_ps(m, a.simdInternal_);
    _mm512_packstorehi_ps(m + 16, a.simdInternal_);
}

static inline SimdFloat gmx_simdcall setZeroF()
{
    return { _mm512_setzero_ps() };
}

static inline SimdFInt32 gmx_simdcall simdLoad(const std::int32_t* m, SimdFInt32Tag)
{
    assert(std::size_t(m) % 64 == 0);
    return { _mm512_load_epi32(m) };
}

static inline void gmx_simdcall store(std::int32_t* m, SimdFInt32 a)
{
    assert(std::size_t(m) % 64 == 0);
    _mm512_store_epi32(m, a.simdInternal_);
}

static inline SimdFInt32 gmx_simdcall simdLoadU(const std::int32_t* m, SimdFInt32Tag)
{
    return { _mm512_loadunpackhi_epi32(_mm512_loadunpacklo_epi32(_mm512_undefined_epi32(), m), m + 16) };
}

static inline void gmx_simdcall storeU(std::int32_t* m, SimdFInt32 a)
{
    _mm512_packstorelo_epi32(m, a.simdInternal_);
    _mm512_packstorehi_epi32(m + 16, a.simdInternal_);
}

static inline SimdFInt32 gmx_simdcall setZeroFI()
{
    return { _mm512_setzero_si512() };
}


template<int index>
static inline std::int32_t gmx_simdcall extract(SimdFInt32 a)
{
    int r;
    _mm512_mask_packstorelo_epi32(&r, _mm512_mask2int(1 << index), a.simdInternal_);
    return r;
}

static inline SimdFloat gmx_simdcall operator&(SimdFloat a, SimdFloat b)
{
    return { _mm512_castsi512_ps(_mm512_and_epi32(_mm512_castps_si512(a.simdInternal_),
                                                  _mm512_castps_si512(b.simdInternal_))) };
}

static inline SimdFloat gmx_simdcall andNot(SimdFloat a, SimdFloat b)
{
    return { _mm512_castsi512_ps(_mm512_andnot_epi32(_mm512_castps_si512(a.simdInternal_),
                                                     _mm512_castps_si512(b.simdInternal_))) };
}

static inline SimdFloat gmx_simdcall operator|(SimdFloat a, SimdFloat b)
{
    return { _mm512_castsi512_ps(_mm512_or_epi32(_mm512_castps_si512(a.simdInternal_),
                                                 _mm512_castps_si512(b.simdInternal_))) };
}

static inline SimdFloat gmx_simdcall operator^(SimdFloat a, SimdFloat b)
{
    return { _mm512_castsi512_ps(_mm512_xor_epi32(_mm512_castps_si512(a.simdInternal_),
                                                  _mm512_castps_si512(b.simdInternal_))) };
}

static inline SimdFloat gmx_simdcall operator+(SimdFloat a, SimdFloat b)
{
    return { _mm512_add_ps(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFloat gmx_simdcall operator-(SimdFloat a, SimdFloat b)
{
    return { _mm512_sub_ps(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFloat gmx_simdcall operator-(SimdFloat x)
{
    return { _mm512_addn_ps(x.simdInternal_, _mm512_setzero_ps()) };
}

static inline SimdFloat gmx_simdcall operator*(SimdFloat a, SimdFloat b)
{
    return { _mm512_mul_ps(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFloat gmx_simdcall fma(SimdFloat a, SimdFloat b, SimdFloat c)
{
    return { _mm512_fmadd_ps(a.simdInternal_, b.simdInternal_, c.simdInternal_) };
}

static inline SimdFloat gmx_simdcall fms(SimdFloat a, SimdFloat b, SimdFloat c)
{
    return { _mm512_fmsub_ps(a.simdInternal_, b.simdInternal_, c.simdInternal_) };
}

static inline SimdFloat gmx_simdcall fnma(SimdFloat a, SimdFloat b, SimdFloat c)
{
    return { _mm512_fnmadd_ps(a.simdInternal_, b.simdInternal_, c.simdInternal_) };
}

static inline SimdFloat gmx_simdcall fnms(SimdFloat a, SimdFloat b, SimdFloat c)
{
    return { _mm512_fnmsub_ps(a.simdInternal_, b.simdInternal_, c.simdInternal_) };
}

static inline SimdFloat gmx_simdcall rsqrt(SimdFloat x)
{
    return { _mm512_rsqrt23_ps(x.simdInternal_) };
}

static inline SimdFloat gmx_simdcall rcp(SimdFloat x)
{
    return { _mm512_rcp23_ps(x.simdInternal_) };
}

static inline SimdFloat gmx_simdcall maskAdd(SimdFloat a, SimdFloat b, SimdFBool m)
{
    return { _mm512_mask_add_ps(a.simdInternal_, m.simdInternal_, a.simdInternal_, b.simdInternal_) };
}

static inline SimdFloat gmx_simdcall maskzMul(SimdFloat a, SimdFloat b, SimdFBool m)
{
    return { _mm512_mask_mul_ps(_mm512_setzero_ps(), m.simdInternal_, a.simdInternal_, b.simdInternal_) };
}

static inline SimdFloat gmx_simdcall maskzFma(SimdFloat a, SimdFloat b, SimdFloat c, SimdFBool m)
{
    return { _mm512_mask_mov_ps(_mm512_setzero_ps(), m.simdInternal_,
                                _mm512_fmadd_ps(a.simdInternal_, b.simdInternal_, c.simdInternal_)) };
}

static inline SimdFloat gmx_simdcall maskzRsqrt(SimdFloat x, SimdFBool m)
{
    return { _mm512_mask_rsqrt23_ps(_mm512_setzero_ps(), m.simdInternal_, x.simdInternal_) };
}

static inline SimdFloat gmx_simdcall maskzRcp(SimdFloat x, SimdFBool m)
{
    return { _mm512_mask_rcp23_ps(_mm512_setzero_ps(), m.simdInternal_, x.simdInternal_) };
}

static inline SimdFloat gmx_simdcall abs(SimdFloat x)
{
    return { _mm512_castsi512_ps(_mm512_andnot_epi32(_mm512_castps_si512(_mm512_set1_ps(GMX_FLOAT_NEGZERO)),
                                                     _mm512_castps_si512(x.simdInternal_))) };
}

static inline SimdFloat gmx_simdcall max(SimdFloat a, SimdFloat b)
{
    return { _mm512_gmax_ps(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFloat gmx_simdcall min(SimdFloat a, SimdFloat b)
{
    return { _mm512_gmin_ps(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFloat gmx_simdcall round(SimdFloat x)
{
    return { _mm512_round_ps(x.simdInternal_, _MM_FROUND_TO_NEAREST_INT, _MM_EXPADJ_NONE) };
}

static inline SimdFloat gmx_simdcall trunc(SimdFloat x)
{
    return { _mm512_round_ps(x.simdInternal_, _MM_FROUND_TO_ZERO, _MM_EXPADJ_NONE) };
}

template<MathOptimization opt = MathOptimization::Safe>
static inline SimdFloat gmx_simdcall frexp(SimdFloat value, SimdFInt32* exponent)
{
    __m512  rExponent;
    __m512i iExponent;
    __m512  result;

    if (opt == MathOptimization::Safe)
    {
        // For the safe branch, we use the masked operations to only assign results if the
        // input value was nonzero, and otherwise set exponent to 0, and the fraction to the input (+-0).
        __mmask16 valueIsNonZero =
                _mm512_cmp_ps_mask(_mm512_setzero_ps(), value.simdInternal_, _CMP_NEQ_OQ);
        rExponent = _mm512_mask_getexp_ps(_mm512_setzero_ps(), valueIsNonZero, value.simdInternal_);
        iExponent = _mm512_cvtfxpnt_round_adjustps_epi32(rExponent, _MM_FROUND_TO_NEAREST_INT,
                                                         _MM_EXPADJ_NONE);
        iExponent = _mm512_mask_add_epi32(iExponent, valueIsNonZero, iExponent, _mm512_set1_epi32(1));

        // Set result to input value when the latter is +-0
        result = _mm512_mask_getmant_ps(value.simdInternal_, valueIsNonZero, value.simdInternal_,
                                        _MM_MANT_NORM_p5_1, _MM_MANT_SIGN_src);
    }
    else
    {
        rExponent = _mm512_getexp_ps(value.simdInternal_);
        iExponent = _mm512_cvtfxpnt_round_adjustps_epi32(rExponent, _MM_FROUND_TO_NEAREST_INT,
                                                         _MM_EXPADJ_NONE);
        iExponent = _mm512_add_epi32(iExponent, _mm512_set1_epi32(1));
        result    = _mm512_getmant_ps(value.simdInternal_, _MM_MANT_NORM_p5_1, _MM_MANT_SIGN_src);
    }

    exponent->simdInternal_ = iExponent;

    return { result };
}

template<MathOptimization opt = MathOptimization::Safe>
static inline SimdFloat gmx_simdcall ldexp(SimdFloat value, SimdFInt32 exponent)
{
    const __m512i exponentBias = _mm512_set1_epi32(127);
    __m512i       iExponent    = _mm512_add_epi32(exponent.simdInternal_, exponentBias);

    if (opt == MathOptimization::Safe)
    {
        // Make sure biased argument is not negative
        iExponent = _mm512_max_epi32(iExponent, _mm512_setzero_epi32());
    }

    iExponent = _mm512_slli_epi32(iExponent, 23);

    return { _mm512_mul_ps(value.simdInternal_, _mm512_castsi512_ps(iExponent)) };
}

static inline float gmx_simdcall reduce(SimdFloat a)
{
    return _mm512_reduce_add_ps(a.simdInternal_);
}

// Picky, picky, picky:
// icc-16 complains about "Illegal value of immediate argument to intrinsic"
// unless we use
// 1) Ordered-quiet for ==
// 2) Unordered-quiet for !=
// 3) Ordered-signaling for < and <=

static inline SimdFBool gmx_simdcall operator==(SimdFloat a, SimdFloat b)
{
    return { _mm512_cmp_ps_mask(a.simdInternal_, b.simdInternal_, _CMP_EQ_OQ) };
}

static inline SimdFBool gmx_simdcall operator!=(SimdFloat a, SimdFloat b)
{
    return { _mm512_cmp_ps_mask(a.simdInternal_, b.simdInternal_, _CMP_NEQ_UQ) };
}

static inline SimdFBool gmx_simdcall operator<(SimdFloat a, SimdFloat b)
{
    return { _mm512_cmp_ps_mask(a.simdInternal_, b.simdInternal_, _CMP_LT_OS) };
}

static inline SimdFBool gmx_simdcall operator<=(SimdFloat a, SimdFloat b)
{
    return { _mm512_cmp_ps_mask(a.simdInternal_, b.simdInternal_, _CMP_LE_OS) };
}

static inline SimdFBool gmx_simdcall testBits(SimdFloat a)
{
    return { _mm512_test_epi32_mask(_mm512_castps_si512(a.simdInternal_),
                                    _mm512_castps_si512(a.simdInternal_)) };
}

static inline SimdFBool gmx_simdcall operator&&(SimdFBool a, SimdFBool b)
{
    return { _mm512_kand(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFBool gmx_simdcall operator||(SimdFBool a, SimdFBool b)
{
    return { _mm512_kor(a.simdInternal_, b.simdInternal_) };
}

static inline bool gmx_simdcall anyTrue(SimdFBool a)
{
    return _mm512_mask2int(a.simdInternal_) != 0;
}

static inline SimdFloat gmx_simdcall selectByMask(SimdFloat a, SimdFBool m)
{
    return { _mm512_mask_mov_ps(_mm512_setzero_ps(), m.simdInternal_, a.simdInternal_) };
}

static inline SimdFloat gmx_simdcall selectByNotMask(SimdFloat a, SimdFBool m)
{
    return { _mm512_mask_mov_ps(a.simdInternal_, m.simdInternal_, _mm512_setzero_ps()) };
}

static inline SimdFloat gmx_simdcall blend(SimdFloat a, SimdFloat b, SimdFBool sel)
{
    return { _mm512_mask_blend_ps(sel.simdInternal_, a.simdInternal_, b.simdInternal_) };
}

static inline SimdFInt32 gmx_simdcall operator&(SimdFInt32 a, SimdFInt32 b)
{
    return { _mm512_and_epi32(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFInt32 gmx_simdcall andNot(SimdFInt32 a, SimdFInt32 b)
{
    return { _mm512_andnot_epi32(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFInt32 gmx_simdcall operator|(SimdFInt32 a, SimdFInt32 b)
{
    return { _mm512_or_epi32(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFInt32 gmx_simdcall operator^(SimdFInt32 a, SimdFInt32 b)
{
    return { _mm512_xor_epi32(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFInt32 gmx_simdcall operator+(SimdFInt32 a, SimdFInt32 b)
{
    return { _mm512_add_epi32(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFInt32 gmx_simdcall operator-(SimdFInt32 a, SimdFInt32 b)
{
    return { _mm512_sub_epi32(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFInt32 gmx_simdcall operator*(SimdFInt32 a, SimdFInt32 b)
{
    return { _mm512_mullo_epi32(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFIBool gmx_simdcall operator==(SimdFInt32 a, SimdFInt32 b)
{
    return { _mm512_cmp_epi32_mask(a.simdInternal_, b.simdInternal_, _MM_CMPINT_EQ) };
}

static inline SimdFIBool gmx_simdcall testBits(SimdFInt32 a)
{
    return { _mm512_test_epi32_mask(a.simdInternal_, a.simdInternal_) };
}

static inline SimdFIBool gmx_simdcall operator<(SimdFInt32 a, SimdFInt32 b)
{
    return { _mm512_cmp_epi32_mask(a.simdInternal_, b.simdInternal_, _MM_CMPINT_LT) };
}

static inline SimdFIBool gmx_simdcall operator&&(SimdFIBool a, SimdFIBool b)
{
    return { _mm512_kand(a.simdInternal_, b.simdInternal_) };
}

static inline SimdFIBool gmx_simdcall operator||(SimdFIBool a, SimdFIBool b)
{
    return { _mm512_kor(a.simdInternal_, b.simdInternal_) };
}

static inline bool gmx_simdcall anyTrue(SimdFIBool a)
{
    return _mm512_mask2int(a.simdInternal_) != 0;
}

static inline SimdFInt32 gmx_simdcall selectByMask(SimdFInt32 a, SimdFIBool m)
{
    return { _mm512_mask_mov_epi32(_mm512_setzero_epi32(), m.simdInternal_, a.simdInternal_) };
}

static inline SimdFInt32 gmx_simdcall selectByNotMask(SimdFInt32 a, SimdFIBool m)
{
    return { _mm512_mask_mov_epi32(a.simdInternal_, m.simdInternal_, _mm512_setzero_epi32()) };
}

static inline SimdFInt32 gmx_simdcall blend(SimdFInt32 a, SimdFInt32 b, SimdFIBool sel)
{
    return { _mm512_mask_blend_epi32(sel.simdInternal_, a.simdInternal_, b.simdInternal_) };
}

static inline SimdFInt32 gmx_simdcall cvtR2I(SimdFloat a)
{
    return { _mm512_cvtfxpnt_round_adjustps_epi32(a.simdInternal_, _MM_FROUND_TO_NEAREST_INT,
                                                  _MM_EXPADJ_NONE) };
}

static inline SimdFInt32 gmx_simdcall cvttR2I(SimdFloat a)
{
    return { _mm512_cvtfxpnt_round_adjustps_epi32(a.simdInternal_, _MM_FROUND_TO_ZERO, _MM_EXPADJ_NONE) };
}

static inline SimdFloat gmx_simdcall cvtI2R(SimdFInt32 a)
{
    return { _mm512_cvtfxpnt_round_adjustepi32_ps(a.simdInternal_, _MM_FROUND_TO_NEAREST_INT,
                                                  _MM_EXPADJ_NONE) };
}

static inline SimdFIBool gmx_simdcall cvtB2IB(SimdFBool a)
{
    return { a.simdInternal_ };
}

static inline SimdFBool gmx_simdcall cvtIB2B(SimdFIBool a)
{
    return { a.simdInternal_ };
}


template<MathOptimization opt = MathOptimization::Safe>
static inline SimdFloat gmx_simdcall exp2(SimdFloat x)
{
    return { _mm512_exp223_ps(_mm512_cvtfxpnt_round_adjustps_epi32(
            x.simdInternal_, _MM_ROUND_MODE_NEAREST, _MM_EXPADJ_24)) };
}

template<MathOptimization opt = MathOptimization::Safe>
static inline SimdFloat gmx_simdcall exp(SimdFloat x)
{
    const __m512 argscale    = _mm512_set1_ps(1.44269504088896341F);
    const __m512 invargscale = _mm512_set1_ps(-0.69314718055994528623F);

    if (opt == MathOptimization::Safe)
    {
        // Set the limit to gurantee flush to zero
        const SimdFloat smallArgLimit(-88.f);
        // Since we multiply the argument by 1.44, for the safe version we need to make
        // sure this doesn't result in overflow
        x = max(x, smallArgLimit);
    }

    __m512 xscaled = _mm512_mul_ps(x.simdInternal_, argscale);
    __m512 r       = _mm512_exp223_ps(
            _mm512_cvtfxpnt_round_adjustps_epi32(xscaled, _MM_ROUND_MODE_NEAREST, _MM_EXPADJ_24));

    // exp2a23_ps provides 23 bits of accuracy, but we ruin some of that with our argument
    // scaling. To correct this, we find the difference between the scaled argument and
    // the true one (extended precision arithmetics does not appear to be necessary to
    // fulfill our accuracy requirements) and then multiply by the exponent of this
    // correction since exp(a+b)=exp(a)*exp(b).
    // Note that this only adds two instructions (and maybe some constant loads).

    // find the difference
    x = _mm512_fmadd_ps(invargscale, xscaled, x.simdInternal_);
    // x will now be a _very_ small number, so approximate exp(x)=1+x.
    // We should thus apply the correction as r'=r*(1+x)=r+r*x
    r = _mm512_fmadd_ps(r, x.simdInternal_, r);
    return { r };
}

static inline SimdFloat gmx_simdcall log(SimdFloat x)
{
    return { _mm512_mul_ps(_mm512_set1_ps(0.693147180559945286226764F),
                           _mm512_log2ae23_ps(x.simdInternal_)) };
}

} // namespace gmx

#endif // GMX_SIMD_IMPL_X86_MIC_SIMD_FLOAT_H