- Qt 6.8
- Qt Core
- C++ Classes
- qfloat16
- Qt 6.8.1 Reference Documentation

# qfloat16 Class

Provides 16-bit floating point support. More...

Header: | `#include <QFloat16>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Core)` `target_link_libraries(mytarget PRIVATE Qt6::Core)`
qmake: | `QT += core`

- List of all members, including inherited members

This class is partially comparable.

This class is partially comparable with float, double, long double, qint8, quint8, qint16, quint16, qint32, quint32, long, unsigned long, qint64, and quint64.

This class is partially comparable with qint128 and quint128.

Comparison with 128-bit integral types is only supported if Qt provides these types.

## Public Functions

`(since 6.1)` | qfloat16(Qt::Initialization)
qfloat16 | copySign(qfloat16 sign) const
bool | isNormal() const

## Related Non-Members

void | qFloatFromFloat16(float *out, const qfloat16 *in, qsizetype len)
void | qFloatToFloat16(qfloat16 *out, const float *in, qsizetype len)
int | qFpClassify(qfloat16 val)
bool | qFuzzyCompare(qfloat16 p1, qfloat16 p2)
`(since 6.5.3)` size_t | qHash(qfloat16 key, size_t seed = 0)
bool | qIsFinite(qfloat16 f)
bool | qIsInf(qfloat16 f)
bool | qIsNaN(qfloat16 f)
qint64 | qRound64(qfloat16 value)
int | qRound(qfloat16 value)
QDataStream & | operator<<(QDataStream &ds, qfloat16 f)
QDataStream & | operator>>(QDataStream &ds, qfloat16 &f)

## Detailed Description

The `qfloat16` class provides support for half-precision (16-bit) floating point data. It is fully compliant with IEEE 754 as a storage type. This implies that any arithmetic operation on a `qfloat16` instance results in the value first being converted to a `float`. This conversion to and from `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.

`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.

Note: On x86 and x86-64 that to get hardware accelerated conversions you must compile with F16C or AVX2 enabled, or use qFloatToFloat16() and qFloatFromFloat16() which will detect F16C at runtime.

## Member Function Documentation

### `[explicit noexcept, since 6.1]` qfloat16::qfloat16(Qt::Initialization)

Constructs a qfloat16 without initializing the value.

This function was introduced in Qt 6.1.

### `[noexcept]` qfloat16 qfloat16::copySign(qfloat16 sign) const

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

### `[constexpr noexcept]` bool qfloat16::isNormal() const

Returns `true` if this `qfloat16` value is finite and in normal form.

See also qFpClassify().

## Related Non-Members

### `[noexcept]` void qFloatFromFloat16(float *out, const qfloat16 *in, qsizetype len)

Converts len qfloat16 from in to floats and stores them in out. Both in and out must have len allocated entries.

This function is faster than converting values one by one, and will do runtime F16C detection on x86 and x86-64 hardware.

### `[noexcept]` void qFloatToFloat16(qfloat16 *out, const float *in, qsizetype len)

Converts len floats from in to qfloat16 and stores them in out. Both in and out must have len allocated entries.

This function is faster than converting values one by one, and will do runtime F16C detection on x86 and x86-64 hardware.

### `[noexcept]` int qFpClassify(qfloat16 val)

This function overloads qFpClassify(float).

Returns the floating-point class of val.

### `[noexcept]` bool qFuzzyCompare(qfloat16 p1, qfloat16 p2)

This function overloads qFuzzyCompare(float, float).

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

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

### `[noexcept, since 6.5.3]` size_t qHash(qfloat16 key, size_t seed = 0)

Returns the hash value for the key, using seed to seed the calculation.

Note: In Qt versions before 6.5, this operation was provided by the qHash(float) overload. In Qt versions 6.5.0 to 6.5.2, this functionality was broken in various ways. In Qt versions 6.5.3 and 6.6 onwards, this overload restores the Qt 6.4 behavior.

This function was introduced in Qt 6.5.3.

### `[noexcept]` bool qIsFinite(qfloat16 f)

This function overloads qIsFinite(float).

Returns true if the `qfloat16` f is a finite number.

### `[noexcept]` bool qIsInf(qfloat16 f)

This function overloads qIsInf(float).

Returns true if the `qfloat16` f is equivalent to infinity.

### `[noexcept]` bool qIsNaN(qfloat16 f)

This function overloads qIsNaN(float).

Returns true if the `qfloat16` f is not a number (NaN).

### `[noexcept]` qint64 qRound64(qfloat16 value)

This function overloads qRound64(float).

Rounds value to the nearest 64-bit integer.

### `[noexcept]` int qRound(qfloat16 value)

This function overloads qRound(float).

Rounds value to the nearest integer.

### QDataStream &operator<<(QDataStream &ds, qfloat16 f)

Writes a floating point number, f, to the stream ds using the standard IEEE 754 format. Returns a reference to the stream.

Note: In Qt versions prior to 6.3, this was a member function on QDataStream.

### QDataStream &operator>>(QDataStream &ds, qfloat16 &f)

Reads a floating point number from the stream ds into f, using the standard IEEE 754 format. Returns a reference to the stream.

Note: In Qt versions prior to 6.3, this was a member function on QDataStream.