On Tue, May 05, 2020 at 01:03:31AM +0200, m...@iae.nl wrote: > On 2020-05-04 17:24, Anton Ertl wrote: > > One issue is how to deal with -infinity (e.g., the result of -1e 0e f/). > > Previously Gforth 0.7.2+glibc produced "-inf" and f1=0 (positive), > > f2=0 (not valid); other libc implementations might lead to different > > results. > > > > gforth 0.7.9_20200423 uses an ecvt_r supplied by us and produces > > "-inf" and f1=-1 (negative), f2=0 (not valid); the new REPRESENT > > currently works in the same way (except that it gives you "-infinity", > > space permitting). > > > > In both systems F. and FS. outputs -in. > > > > iForth behaves like gforth 0.7.2. > > > > VFX produces "Inf" and f1=-1, f2=0. > > > > The VFX behaviour looks like the most sensible one to me, but it might > > affect code that uses REPRESENT; we can change our own code > > accordingly, but what about your code? Do you have code that uses > > REPRESENT and that has been designed for a specific behaviour when > > getting -infinity? > > ( Bernd clarified f1 and f2. ) > > > VFX produces "Inf" and f1=-1, f2=0. > > I think I will fix iForth (in due time) to give "-INF", f1=-1 f2=-1. > It does not make sense to me to claim f2=0 when the item has a sign and > gives valid output for many operations.
I think that putting the sign in f1, not in the string is most appropriate, because that's the same as for finite numbers (-1e produces "10..." and f1=-1). As for f2, with IEEE arithmetic there is no number that's strictly invalid; IEEE 754 defines a meaning for every bit pattern. So what should we return as f2? 1) Always return -1? That's not useful, and contrary to existing practice. 2) Return -1 for finite and infinite numbers, and 0 for NaNs. That's arguable, but contrary to existing practice. Moreover, what would be the use of this behaviour? 3) Return -1 for finite numbers, and 0 for infinities and NaNs. That's existing practice, and is useful for indicating that the that the string result consists of digits and that the n (exponent) result of REPRESENT is actually meaningful. - anton
