When used in a C or C++ expression, an __fp16 type is promoted to
single precision. Subsequent promotion to double precision can occur if required by one
of the operands.
A single precision value can be converted to __fp16. A double
precision value is converted to single precision and then to __fp16,
that could involve double rounding. This reflects the lack of direct double-to-16-bit
conversion in the ARM architecture.
When using fpmode=fast, no floating-point exceptions are raised when
converting to and from half-precision floating-point format.
Function formal arguments cannot be of type __fp16. However,
pointers to variables of type __fp16 can be used as function formal
argument types.
__fp16 values can be passed as actual function arguments. In this
case, they are converted to single-precision values.
__fp16 cannot be specified as the return type of a function.
However, a pointer to an __fp16 type can be used as a return
type.
An __fp16 value is converted to a single-precision or
double-precision value when used as a return value for a function that returns a
float or double.
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