OpenEuphoria

Re: Passing Floats by Value

• Posted by David Guy <dguy at MINDSPRING.COM> Jan 20, 2000
• 500 views

On Wed, 19 Jan 2000 21:13:26 -0500, Robert Craig <rds at ATTCANADA.NET> wrote:

>David Guy writes:
>> How do I pass a 4-byte floating point value from
>> Euphoria to a C routine?
>
>Euphoria only supports passing floating-point atoms to C routines
>in the form of C doubles (8 bytes). From my experience,
>it's extremely rare that a C routine will pass float arguments
>(4-bytes), and even if it did, I believed (until now) that most,
>if not all, C compilers automatically promote float arguments
>to double before passing them. I suppose I could support
>passing atoms as C floats in the next release.
>
>Meanwhile, here's a kludge that you can try.
>- convert each argument, a, as:
>         a = bytes_to_int(atom_to_float32(a))
>
>- define the C function in Euphoria as if it takes C_INT's
>  as arguments
>
>- pass each argument, a, as a C_INT

You're kludge works! :)

If I "link" to the routine in either of the following ways:

  constant m_myFunc = define_c_proc(m_DLL, "_myFunc@8", {C_FLOAT, C_FLOAT})
    or
  constant m_myFunc = define_c_proc(m_DLL, "_myFunc@8", {C_INT, C_INT})

and then call the routine like so:

  c_proc(m_myFunc,
    {bytes_to_int(atom_to_float32(1.0)),
     bytes_to_int(atom_to_float32(1.0))} )

the following prints out:

 1.000000 1.000000


As to supporting the passing of atoms as C floats,...YES please do!
It would be nice if when a float was specified, a float was passed. :)
It can't be that difficult for Euphoria to convert an atom down to a float
before passing it, and I'm sure it would be much faster, and certainly
cleaner and more straight forward, than the above kludge.

Thanks for the help,
David Guy