Re: Cost of handling misaligned access

On Tue, 18 Feb 2025 21:09:54 +0000, Terje Mathisen wrote:

MitchAlsup1 wrote:

On Tue, 18 Feb 2025 13:07:39 +0000, Michael S wrote:
>

On Tue, 18 Feb 2025 02:55:33 +0000
mitchalsup@aol.com (MitchAlsup1) wrote:

>
It takes Round Nearest Odd to perform Kahan-Babashuka Summation.
>

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Are you aware of any widespread hardware that supplies Round to Nearest
with tie broken to Odd? Or of any widespread language that can request
such rounding mode?

>
No, No
>

Until both, implementing RNO on niche HW looks to me as wastage of both
HW resources and of space in your datasheet.

>
They way I implement it, it is only an additional 10± gates.

>
With discrete logic, it should be identical to RNE, except for flipping
the ulp bit when deciding upon the rounding direction, right?

Yes,

With a full 4-bit lookup table you need a few more gates, but that is
still the obvious way to implement rounding in SW. (It is only ceil()
and floor() that requires the sign bit as input, the remaining rounding
modes can make do with ulp+guard+sticky.

sign+ULP+Gard+sticky is all you ever need for any rounding mode
IEEE or beyond.

Terje