The built-in function `signbit`

tests for sign bit.
For the forms not dependent on the
cl_khr_fp16
extension, the scalar
version of the function returns a 1 if the sign bit in the float is set else returns
0. The vector version of the function returns the following for each component in
float`n`

: -1 (i.e. all bits set) if the sign bit in the
float is set else returns 0.

For the forms enmabled by the
cl_khr_fp16
extension,
the function returns a 1 if the sign bit in the half is set else returns
0. The vector version of the function returns the following for each component in
half`n`

: -1 (i.e. all bits set) if the sign bit in the
half is set else returns 0.

If an implementation extends this specification to support IEEE-754 flags or
exceptions, then all built-in relational functions shall proceed without raising the
`invalid`

floating-point exception when one or more of the operands
are NaNs.

The built-in relational functions are extended with cl_khr_fp16 to include versions that take half, and half{2|3|4|8|16} as arguments.

The function returns a 0 if the specified relation is `false`

and a 1
if the specified relation is `true`

for scalar argument types. These
functions shall return a 0 if the specified relation is `false`

and a -
1 (i.e. all bits set) if the specified relation is `true`

for vector
argument types.

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