4.7.3. __builtin_constant_p
This builtin function determines if a value is known to be
constant at compile-time.
Note
This builtin function is a GNU compiler extension that is
supported by the ARM compiler.
Supported in GNU mode only.
int __builtin_constant_p(...)
Where:
...is the argument whose value is to be tested.
__builtin_constant_p returns the integer
1 if the argument is known to be a compile-time constant and 0 if
it is not known to be a compile-time constant.
A return value of 0 does not indicate that the value is not
a constant, but that the compiler cannot prove it is a constant
with the specified value of the -O option.
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