[Bug: 21.4.19] Bruised floating point numbers from string-to-int

[Raymond Toy]

>>>>> "sjt" == Stephen J Turnbull <stephen at xemacs.org> writes:

>>>>> "Raymond" == Raymond Toy <raymond.toy at ericsson.com> writes:
    Raymond> If you don't get 1.0, you have a badly broken system, if
    Raymond> you are using IEEE 754.  0.125 and 0.875 can be
    Raymond> represented exactly, and so can their sum.  If you don't
    Raymond> get 1.0, then your reader is broken or your printer.  Or,
    Raymond> perhaps, + is broken. :-)

    sjt> But what if I get 1.000?  Where is something broken?  My point is that
    sjt> a conscientious human presented with the problem

Oops.  Sorry.  I misinterpreted what you wanted.  The true answer is
exactly 1, but you wanted it printed out with trailing zeroes.

    sjt> Yup.  `string-to-int' is an alias for `string-to-number',
    sjt> which is (ultimately) just a wrapper around the platform's
    sjt> printf implementation.
    sjt> What you get is what you get.

    Raymond> But it is possible to do a better job.
    Raymond> CMUCL prints "8.18e-1" exactly like that.

    sjt> Which is *arguably wrong* because you've lost a digit of precision.  I
    sjt> really don't think *Rodney* can win this way.  Yes, *we* could get
    sjt> prettier output for the occasional number, but he's working with
    sjt> tables.

I think this is a similar confusion on my part.  I meant that the
result is printed as 0.818 instead of 0.8179999...

    sjt> Microsoft's apparent do, Unices don't.  Not worth our effort to
    sjt> replace them, I suggest, unless somebody != me :-) wants to look up
    sjt> the various algorithms *and* present the rationales, *and* document
    sjt> the algorithms so people know what to expect, *as well as* update our

The algorithm for printing floating point numbers accurately is
available in C on the web, along with a document describing the
algorithm.  (Look for Dybvig.)

But I don't use xemacs for floating point work so I have no intentions
of doing this either. :-)

Ray