Extract mantissa and exponent from `x`

. For each component the mantissa
returned is a float with magnitude in the interval [1/2, 1) or 0. Each component of
`x`

equals mantissa returned * 2^{exp}.

The built-in math functions are not affected by the prevailing rounding mode in the calling environment, and always return the same value as they would if called with the round to nearest even rounding mode.

An application that wants to use half
and half* n*
types will need to include the

```
#pragma OPENCL EXTENSION
cl_khr_fp16 : enable
```

directive.
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