Re: Parsing timestamps?

On 14/07/2025 4:04 pm, 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.

So in mandating bit-identical results, not only in calculations but also
input/output, IEEE 754 is all about giving the illusion of truth in
floating-point when, if anything, they should be warning users don't be
fooled.