Martin Husemann <martin%duskware.de@localhost> 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 implementation? > - 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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