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Re: Support for non-default rounding modes in the softfloat layer

Martin Husemann <> writes:

> On Tue, Apr 30, 2013 at 01:28:47PM +0200, ????? ???????????? wrote:
>> A lot of scientific software uses non-default rounding modes as
>> optimisation short cut. but then this is software which runs on high
>> end hardware a la SPARC T5, SPARC64, NEC SX9 or the very latest
>> IA32/AMD64 hardware.
> Ok, but the basic questions are:
>  - does it switch between non standard rounding modes often?

Does the standard specify a default, or is that up to the

>  - does it use different rounding modes in different threads?

My guess from limited experience is that a single big program has a
planned rounding mode and it just gets set once for the program.

> But, what I wonder most:
>  - would the per-thread rounding mode penalty even matter if doing softfloat?

Probably not.  But can you point to something in standards or existing
practice that makes per-thread rounding mode make any sense at all?
This discussion is the first I've heard of the concept.

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