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Re: Implementor support for the binary interchange formats

IBM zSeries supports binary128 in hardware as well as binary32, binary64, decimal64 and decimal128. Almost all architected arithmetic operations are completely executed in hardware with the exception of conversions between decimal and binary floating-point formats and a divide-to-integer operation. The binary dataflow is optimized for binary64 requiring multiple passes for binary128, but all controlled by hardware. The decimal dataflow is wider and directly supports decimal128.

Eric Schwarz


stds-754@xxxxxxxx wrote on 03/01/2011 04:44:56 AM:

> From: "Hossam A. H. Fahmy" <hfahmy@xxxxxxxxxxxxxxxxxxxxxxx>

> To: Charles Stevens <charles.stevens@xxxxxxxx>
> Cc: marius.cornea@xxxxxxxxx, IEEE 754 <stds-754@xxxxxxxxxxxxxxxxx>
> Date: 03/01/2011 04:51 AM
> Subject: Re: Implementor support for the binary interchange formats
> Sent by: stds-754@xxxxxxxx
> Dear all,

> 2011/2/28 Charles Stevens <charles.stevens@xxxxxxxx>
> I'm not talking about the binary ENCODING (e.g., "decimal128 using
> binary encoding"); already understood there were implementations
> providing that.
> What I'm talking about is "binary128 format" ITSELF, specifically as
> distinct from decimal128 using EITHER encoding. 

> I didn't see an answer to your question yet so here is my answer.
> All the HARDWARE for general purpose computers that I know of and
> used does NOT have binary128 directly in the processor. That means
> Intel, AMD, and Sun processors. I am almost sure that it is the same
> case for IBM, HP, and Fujitsu but I will leave it to those working
> at such companies or using those platforms to confirm it.
> Most processors (for general purpose computers) support binary64
> directly in the hardware (registers, adders, datapath, rounding
> logic, ...) and can provide binary32 as well since it is just a
> narrower format. Binary128 is a new feature added in IEEE754-2008
> just as the decimal64 and decimal128 are new features. Hence, some
> HW providers may opt to support binary128 directly in their future processors.
> However, binary128 may be supported now on these platforms via low
> level software libraries or microcode that use the underlying
> hardware designed for the 64 bits width and provide the correct
> result but with a longer execution time compared to binary64.
> I hope this answers your question.
> With that said, I also note that decimal is not much different. IBM
> and SilMinds are the only two companies that provide hardware units
> for decimal and both use DPD. As far as I know, (Michel please
> confirm or deny), IBM's HW has direct support for decimal64 while
> decimal128 needs similar low level SW to give the correct  answers.
> SilMinds has direct decimal128 and decimal64 in their HW accelerator cards.
> --
> Hossam

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