Wrong RTL instruction deleted

[Giovanni Bajo]

Robert Dewar <dewar@adacore.com> wrote:

> The corresponding Ada program:
>
>    function Foo return Float is
>       function To_Float is new Unchecked_Conversion (Unsigned_32, Float);
>       MASK : unsigned := 16#8000_0000#;
>    begin
>       return To_Float (MASK);
>    end Foo;
>
> is certainly 100% valid since the value converted is a valid
> value of the target type.

This is getting off-topic quick, but there is no easy way to do this in C++.
With GNU C/C++, you can use unions:

union IntFloat {
    unsigned int i; float f;
};

float To_Float(unsigned int mask)
{
    IntFloat if;
    if.i = mask;
    return if.f;
}

but this is actually undefined behaviour per the ISO C++ Standard. Sometimes
ago, I proposed this new syntax as an extension on comp.std.c++:

float To_Float(unsigned int mask)
{
    return reinterpret_cast<float>(mask);
}

but people didn't like it (Gaby Dos Reis among all, IIRC). The funny thing
is, I really really really really need to be able to do something like this,
and there is still no way to do this portably in C++.
-- 
Giovanni Bajo