FW: Couple of things

[Daniel Leuck]

Forwarded...

 

Eric -  I added you to the list so you can participate in this discussion.

 

I will be flying all day tomorrow.  I'll respond after I am back and
settled.

 

  _____  

From: E M [mailto:eric at sulawesi.net] 
Sent: Saturday, November 11, 2006 11:17 PM
To: Daniel Leuck; sdl-developers at ikayzo.org
Cc: eric at sulawesi.net
Subject: RE: Couple of things

 

I am not an expert on numerical analysis, and have not worked on SDL. I
wrote some code which used and compared GMP and OpenSSL BigNum libraries,
which is my only hook into this thread...

29 decimal digits of precision is equivalent to 96 binary digits of
precision. Therefore it seems reasonable to use GMP (or appropriate
equivalent) with precision set to 0x60.

However, the exponent in GMP is always a word--32 or 64 bits, where the
"decimal" type is claiming 32 bits (128 - 96). So GMP in this case would
only be equivalent on 32 bit systems.

GMP does not claim to conform to any specific floating point standard (much
less THE gold standard  IEEE754). Nor does GMP even claim that the same
operations will give the same results on architectures with different native
word sizes.

This might be a minor point if the implementation of SDL allows platforms to
do calculations to the best of their abilities, instead of with exact
equivalency. 

Do the Java and C# implementations give the same results when operating on
128 bit fp quantities?

One route could be to restrict SDL to floats and doubles, and make this 128
bit (C#) fp operation an extension. That way the C++ port gets off the
ground without having to worry about it :)

Eric

 

> Also, there is currently no portable way to implement the 128 bit decimal
type in SDL C++, that I

> know of, short of bundling the GNU MP library.

 

That's a tough one.  Do any other list members have suggestions?  Eric?  A
description of the C# decimal type is here:
http://msdn2.microsoft.com/en-US/library/364x0z75.aspx 

 

  _____  

From: Jesse Weaver [mailto:pianohacker at gmail.com] 
Sent: Saturday, November 11, 2006 2:41 PM
To: SDL_Developers
Subject: Couple of things

 

My own two cents on a couple of things:
Has anyone done any testing to make sure that the .NET port works with Mono?
If this is a priority, I imagine it wouldn't be too much work, and I could
compile it on my machine.
Also, there is currently no portable way to implement the 128 bit decimal
type in SDL C++, that I know of, short of bundling the GNU MP library. What
should I do?

-- 
Jesse

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