Re: Parsing timestamps?

On Mon, 14 Jul 2025 06:04:13 GMT
anton@mips.complang.tuwien.ac.at (Anton Ertl) wrote:

dxf <dxforth@gmail.com> 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