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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: binary128 implementation
Date: Fri, 24 May 2024 23:29:13 +0000
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BGB-Alt wrote:

Don't you EVER snip useless crap off the top of your posts ??

> In my case, BGBCC supports __int128 operations whether or not the ALUX 
> instructions are enabled (along with _BitInt, *1).

I am guessing that your CPU does not do 128, 256, 384 bit calculations
natively, but the compiler supports those by emitting sequences of 
instructions.

> *1:
>    _BitInt(56)  x0;  //maps to 64-bit
>    _BitInt(64)  x1;  //maps to 64-bit
>    _BitInt(80)  x2;  //maps to 128-bit
>    _BitInt(128) x3;  //maps to 128-bit
>    _BitInt(160) x4;  //maps to 256-bit
>    _BitInt(256) x5;  //maps to 256-bit
>    _BitInt(272) x6;  //maps to 384-bit
>    ...
> All sizes beyond 256 bit mapping to the next integer multiple of 128 
> bits. The 256-bit type is special, in that it has its own dedicated 
> logic, but exists via the _BitInt type. For 384 and beyond, generic 
> logic is used that deals with any size value, but is slower.

> Can note that in my implementation, BitInt does not enforce modulo 
> behavior in the case of overflow (it is modulo only to the size of the 
> container; enforcing odd-bit modulo behavior would add a fair bit of 
> cost to using them).

The multi-precision arithmetic in My 66000 supports rather arbitrary 
width calculations, although only those 256-bits and smaller can be 
considered fast and/or efficient. In addition, both signed and 
unsigned multi-precision arithmetic is available.


>> Terje
>>