path: root/src/corelib/global/qfloat16.cpp

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#include "qfloat16.h"
#include "private/qsimd_p.h"
#include <cmath> // for fpclassify()'s return values

QT_BEGIN_NAMESPACE

/*!
    \headerfile <QFloat16>
    \title 16-bit Floating Point Support
    \ingroup funclists
    \brief The <QFloat16> header file provides 16-bit floating point support.

    This header file provides support for half-precision (16-bit) floating
    point data with the class \c qfloat16.  It is fully compliant with IEEE
    754 as a storage type.  This implies that any arithmetic operation on a
    \c qfloat16 instance results in the value first being converted to a
    \c float.  This conversion to and from \c float is performed by hardware
    when possible, but on processors that do not natively support half-precision,
    the conversion is performed through a sequence of lookup table operations.

    \c qfloat16 should be treated as if it were a POD (plain old data) type.
    Consequently, none of the supported operations need any elaboration beyond
    stating that it supports all arithmetic operators incident to floating point
    types.

    \since 5.9
*/

/*!
    \macro QT_NO_FLOAT16_OPERATORS
    \relates <QFloat16>
    \since 5.12.4

    Defining this macro disables the arithmetic operators for qfloat16.

    This is only necessary on Visual Studio 2017 (and earlier) when including
    \c {<QFloat16>} and \c{<bitset>} in the same translation unit, which would
    otherwise cause a compilation error due to a toolchain bug (see
    [QTBUG-72073]).
*/

/*!
    \fn bool qIsInf(qfloat16 f)
    \relates <QFloat16>

    Returns true if the \c qfloat16 \a {f} is equivalent to infinity.

    \sa qIsInf
*/

/*!
    \fn bool qIsNaN(qfloat16 f)
    \relates <QFloat16>

    Returns true if the \c qfloat16 \a {f} is not a number (NaN).

    \sa qIsNaN
*/

/*!
    \fn bool qIsFinite(qfloat16 f)
    \relates <QFloat16>

    Returns true if the \c qfloat16 \a {f} is a finite number.

    \sa qIsFinite
*/

/*!
    \internal
    \since 5.14
    bool qfloat16::isInf() const noexcept

    Tests whether this \c qfloat16 value is an infinity.

    \sa qIsInf()
*/

/*!
    \internal
    \since 5.14
    bool qfloat16::isNaN() const noexcept

    Tests whether this \c qfloat16 value is "not a number".

    \sa qIsNaN()
*/

/*!
    \since 5.14
    bool qfloat16::isNormal() const noexcept

    Tests whether this \c qfloat16 value is finite and in normal form.

    \sa qFpClassify()
*/

/*!
    \internal
    \since 5.14
    bool qfloat16::isFinite() const noexcept

    Tests whether this \c qfloat16 value is finite.

    \sa qIsFinite()
*/

/*!
    \since 5.15
    \fn qfloat16::copySign(qfloat16 sign) const noexcept

    Returns a qfloat16 with the sign of \a sign but the rest of its value taken
    from this qfloat16. Serves as qfloat16's equivalent of std::copysign().
*/

/*!
    \internal
    \since 5.14
    Implements qFpClassify() for qfloat16.

    \sa qFpClassify()
*/
int qfloat16::fpClassify() const noexcept
{
    return isInf() ? FP_INFINITE : isNaN() ? FP_NAN
        : !(b16 & 0x7fff) ? FP_ZERO : isNormal() ? FP_NORMAL : FP_SUBNORMAL;
}

/*! \fn int qRound(qfloat16 value)
    \relates <QFloat16>

    Rounds \a value to the nearest integer.

    \sa qRound
*/

/*! \fn qint64 qRound64(qfloat16 value)
    \relates <QFloat16>

    Rounds \a value to the nearest 64-bit integer.

    \sa qRound64
*/

/*! \fn bool qFuzzyCompare(qfloat16 p1, qfloat16 p2)
    \relates <QFloat16>

    Compares the floating point value \a p1 and \a p2 and
    returns \c true if they are considered equal, otherwise \c false.

    The two numbers are compared in a relative way, where the
    exactness is stronger the smaller the numbers are.
 */

#if QT_COMPILER_SUPPORTS(F16C)
static inline bool hasFastF16()
{
    // All processors with F16C also support AVX, but YMM registers
    // might not be supported by the OS, or they might be disabled.
    return qCpuHasFeature(F16C) && qCpuHasFeature(AVX);
}

extern "C" {
#ifdef QFLOAT16_INCLUDE_FAST
#  define f16cextern    static
#else
#  define f16cextern    extern
#endif

f16cextern void qFloatToFloat16_fast(quint16 *out, const float *in, qsizetype len) noexcept;
f16cextern void qFloatFromFloat16_fast(float *out, const quint16 *in, qsizetype len) noexcept;

#undef f16cextern
}

#elif defined(__ARM_FP16_FORMAT_IEEE) && defined(__ARM_NEON__)
static inline bool hasFastF16()
{
    return true;
}

static void qFloatToFloat16_fast(quint16 *out, const float *in, qsizetype len) noexcept
{
    __fp16 *out_f16 = reinterpret_cast<__fp16 *>(out);
    qsizetype i = 0;
    for (; i < len - 3; i += 4)
        vst1_f16(out_f16 + i, vcvt_f16_f32(vld1q_f32(in + i)));
    SIMD_EPILOGUE(i, len, 3)
        out_f16[i] = __fp16(in[i]);
}

static void qFloatFromFloat16_fast(float *out, const quint16 *in, qsizetype len) noexcept
{
    const __fp16 *in_f16 = reinterpret_cast<const __fp16 *>(in);
    qsizetype i = 0;
    for (; i < len - 3; i += 4)
        vst1q_f32(out + i, vcvt_f32_f16(vld1_f16(in_f16 + i)));
    SIMD_EPILOGUE(i, len, 3)
        out[i] = float(in_f16[i]);
}
#else
static inline bool hasFastF16()
{
    return false;
}

static void qFloatToFloat16_fast(quint16 *, const float *, qsizetype) noexcept
{
    Q_UNREACHABLE();
}

static void qFloatFromFloat16_fast(float *, const quint16 *, qsizetype) noexcept
{
    Q_UNREACHABLE();
}
#endif
/*!
    \since 5.11
    \relates <QFloat16>

    Converts \a len floats from \a in to qfloat16 and stores them in \a out.
    Both \a in and \a out must have \a len allocated entries.
*/
Q_CORE_EXPORT void qFloatToFloat16(qfloat16 *out, const float *in, qsizetype len) noexcept
{
    if (hasFastF16())
        return qFloatToFloat16_fast(reinterpret_cast<quint16 *>(out), in, len);

    for (qsizetype i = 0; i < len; ++i)
        out[i] = qfloat16(in[i]);
}

/*!
    \since 5.11
    \relates <QFloat16>

    Converts \a len qfloat16 from \a in to floats and stores them in \a out.
    Both \a in and \a out must have \a len allocated entries.
*/
Q_CORE_EXPORT void qFloatFromFloat16(float *out, const qfloat16 *in, qsizetype len) noexcept
{
    if (hasFastF16())
        return qFloatFromFloat16_fast(out, reinterpret_cast<const quint16 *>(in), len);

    for (qsizetype i = 0; i < len; ++i)
        out[i] = float(in[i]);
}

QT_END_NAMESPACE

#include "qfloat16tables.cpp"
#ifdef QFLOAT16_INCLUDE_FAST
#  include "qfloat16_f16c.c"
#endif