[ieeefp-tests-devel] Re: [ieeefp-tests-cvs] CVS update: ieeefp-tests/ieeefp-tests.lisp

[Raymond Toy]

>>>>> "Christophe" == Christophe Rhodes <csr21 at cam.ac.uk> writes:

    Christophe> Raymond Toy <rtoy at common-lisp.net> writes:
    >> o Add support for hypot.  This is used to test Lisp's ABS function on
    >> complex values.

    Christophe> Cool.  I have ucblib-style input files for trunc()/FTRUNCATE in single
    Christophe> and double precision.  Do you think they should go into ucb/ucblib/,
    Christophe> or should we treat that as pristine and place additions somewhere
    Christophe> else?

My preference is to keep ucblib pristine.  But if you don't that's ok.

    Christophe> Perhaps this allows me to bring up a couple of ideas for things which
    Christophe> should live in the IEEE754 package?  Ideas:
    Christophe>   * specialised condition types: IEEE754:DIVISION-BY-ZERO and
    Christophe>     friends.  The standard document says that it would be nice for
    Christophe>     programs to be able to find the faulting instruction and the
    Christophe>     operands from the handler; it would be nice to attempt to support
    Christophe>     this, at least for the IEEE-specified operations (+, -, *, /, sqrt
    Christophe>     and round-to-integer);

This is a good idea.  CMUCL/sparc already supports this, I think, but
doesn't give the address of the faulting instruction, although it
could.

It's a problem with x86 since the exceptions happen at the NEXT FP
instruction, so the operands could have been destroyed before then.  I
think I tried to implement this for x86 long ago, but it didn't seem
to work very well for some reason that I can't recall.

    Christophe>   * functions to get at the individual bits in the fields:
    Christophe>     IEEE:DOUBLE-FLOAT-EXPONENT and friends.  (I'm aware that the
    Christophe>     exponent field is biased; that makes design interesting)

Provide both, perhaps?  I note that cmucl's idea of the bias value is
off by one from the bias value I see in most documents about IEEE754.

    Christophe>   * (maybe) implementations of functions which don't have any
    Christophe>     corresponding analogue in CL: IEEE754:LOG10?  IEEE754:HYPOT?
    Christophe>     Maybe inspiration could be drawn from the C99 and C0X standards in
    Christophe>     this regard.

Yes.  From a peek at glibc's log10, it looks reasonably
straight-forward.  I think hypot could be done using complex-sqrt
that's already in cmucl/sbcl.  At least the hypot tests all pass, and
we use complex-sqrt for abs of a complex number.

Should we provide for nextafter and copysign?  Well, copysign is the
same as Lisp's float-sign, with the args in the opposite order.
There's also scalb (basically scale-float) and log2.  We should
provide those as well, I guess.

Ray