From: peter.noreply@tin.it
On Mon, 14 Jul 2025 06:04:13 GMT
anton@mips.complang.tuwien.ac.at (Anton Ertl) wrote:
> dxf writes:
> >On 13/07/2025 7:01 pm, Anton Ertl wrote:
> >> ...
> >> For Forth, Inc. and MPE AFAIK their respective IA-32 Forth system
> >> was the only one with hardware FP for many years, so there
> >> probably was little pressure from users for bit-identical results
> >> with, say, SPARC, because they did not have a Forth system that
> >> ran on SPARC.
> >
> >What do you mean by "bit-identical results"? Since SSE2 comes
> >without transcendentals (or basics such as FABS and FNEGATE) and
> >implementers are expected to supply their own, if anything, I expect
> >results across platforms and compilers to vary.
>
> There are operations for which IEEE 754 specifies the result to the
> last bit (except that AFAIK the representation of NaNs is not
> specified exactly), among them F+ F- F* F/ FSQRT, probably also
> FNEGATE and FABS. It does not specify the exact result for
> transcendental functions, but if your implementation performs the same
> bit-exact operations for computing a transcendental function on two
> IEEE 754 compliant platforms, the result will be bit-identical (if it
> is a number). So just use the same implementations of transcentental
> functions, and your results will be bit-identical; concerning the
> NaNs, if you find a difference, check if the involved values are NaNs.
>
> - anton
This of course excludes the use of libm or other math libraries provided
by the distribution. They will change between releases.
I have with success used fdlibm, that is the base for many others. I
gives max 1 ulp rounding error. I have now also tested the core-math
project https://gitlab.inria.fr/core-math/core-math This gives
correctly rounded functions at the cost of being 10 times the compiled
size! A complete library with trig, log, pow etc comes in at 500k.
Peter
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