[Ironpython-users] IronPython float_info values (was: IronPython always in 32-bit mode on 64bit machine even when running ipy64.exe)

[Markus Schaber]

Hi,

Maybe we'd use some conditional initializiation, checking for the properties of the number, like the following:

        // The definition of Epsion and MinValue differ between .NET and Python/C,
        // so we need to define our own values.
        // Approx. -2.2204460492503131e-16 - the byte order reversed value is approx.
        // 2.2290265677773679e-319, so this code delivers the correct value independently
        // of the byte order of the machine.
        private static readonly double EPSILON = Math.Max(
            System.BitConverter.Int64BitsToDouble(0x3cb0000000000000),
            System.BitConverter.Int64BitsToDouble(0x000000000000b03c));
        // Approx. 2.2250738585072014e-308 - the byte-order reversed value is approx.
        // 2.0236928853657458e-320, so this code delviers the correct value independently
        // of the byte order of the machine.
        private static readonly double MIN = Math.Max(
            System.BitConverter.Int64BitsToDouble(0x0010000000000000),
            System.BitConverter.Int64BitsToDouble(0x0000000000001000));

        public static floatinfo float_info = new floatinfo(Double.MaxValue, 1024, 308, MIN, -1021, -307, 15, 53, EPSILON, 2, 1);

This trick relies on the fact that for the given values, the reversed byte order produces an zero-Exponent, which are denormalized numbers, and in both cases, the wanted number is a normalized one which (by definition) is larger than the denormalized one.

This code is as elegant as checking for the endianness explicitly, and we are even safe for machines where the integer and float endianness are different (see https://en.wikipedia.org/wiki/Endianness#Floating-point_and_endianness - although I doubt that those hardware is relevant for our user base...) :)



Best regards

Markus Schaber

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Von: Slide [mailto:slide.o.mix at gmail.com]
Gesendet: Mittwoch, 8. Mai 2013 22:44
An: Jeff Hardy
Cc: Markus Schaber; Curt Hagenlocher; ironpython-users at python.org
Betreff: Re: [Ironpython-users] IronPython float_info values (was: IronPython always in 32-bit mode on 64bit machine even when running ipy64.exe)

Unless Microsoft really wants pain and anguish, they are likely running in little endian mode. I've never run across an ARM setup that actually runs in big endian (nor do I want to), so I'm pretty sure its little endian. I'd be more than willing to test an app on my phone since Windows Phone is crap anyway, so you couldn't damage it any worse than it is now :-)

Alex

On Wed, May 8, 2013 at 12:54 PM, Jeff Hardy <jdhardy at gmail.com<mailto:jdhardy at gmail.com>> wrote:
On Wed, May 8, 2013 at 9:15 AM, Markus Schaber <m.schaber at codesys.com<mailto:m.schaber at codesys.com>> wrote:
> Hi,
>
>
>
> The main problem for now is that I can't test whatever solution we find,
> because I don't have access to any hardware with non-intel Byte Order and a
> Microsoft .NET. (I don't want to rely on Mono for this test...)
Is ARM big-endian? If so, any Windows 8 ARM tablet (i.e. Surface RT)
or Windows Phone should do. Heck, even the emulator might do. It
shouldn't be too hard to whip up an app that prints those two values,
and I think Alex has a Windows Phone if he'd be willing to test it.

If ARM is little-endian (or Windows/ARM runs in little-endian mode)
then I don't think it matters; we'd have to try Mono on a PowerPC or
something like that.

- Jeff



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