[Armedbear-devel] EQUALP raises type-error comparing large bignums to floats (patch attached)

[Erik Huelsmann]

Hi Massimiliano,

On Tue, Jan 27, 2015 at 11:38 PM, Massimiliano Ghilardi <
massimiliano.ghilardi+abcl at gmail.com> wrote:

> On 01/26/15 07:40, Mark Evenson wrote:
>
>>
>>  On 25 Jan 2015, at 20:19, Massimiliano Ghilardi <
>>> massimiliano.ghilardi+abcl at gmail.com> wrote:
>>>
>>> Massimiliano Ghilardi
>>>
>>
>> Nice fix.  Promoted as [14749][].
>>
>> Need to release a abcl-1.3.2 real soon now…
>>
>> [14749]: http://abcl.org/trac/changeset/14749
>>
>
> Thanks Mark.
>
> My patch stops EQUALP from signaling errors on "impossible"
> bignum-to-float comparisons, i.e. between floats and bignums larger than
> the biggest representable floats.
>
> Anyway, it does not fix an existing bug for "possible" comparisons, i.e.
> between floats and bignums in the range representable by floats.
>
> The usual CLHS
> file:///home/max/SW/lisp/docs-lisp/HyperSpec/Body/f_equalp.htm#equalp
> tells that EQUALP on two numbers is the same as =.
>
> There are cases where ABCL does not follow it:
>
> CL-USER> (= most-positive-single-float 340282346638528859811704183484
> 516925440)
> T
>
> CL-USER> (equalp most-positive-single-float 340282346638528859811704183484
> 516925440)
> T ;; correct :)
>
> CL-USER> (= most-positive-single-float 340282346638528859811704183484
> 516925439)
> NIL
>
> EQUALP behaves differently from =, because (EQUALP bignum float) converts
> the bignum to float, losing precision:
>
> CL-USER> (equalp most-positive-single-float 340282346638528859811704183484
> 516925439)
> T ;; incorrect :(
>
>
>
> Digging more reveals further inconsistencies...
>
> CL-USER> (= 1.0 #C(1.0 0.0))
> T
>
> CL-USER> (equalp 1.0 #C(1.0 0.0))
> NIL ;; again :(
>
> The fix is conceptually simple: for all the number tower, EQUALP must use
> the same algorithm as =, with the only difference that it must never throw.
>
> I am not sure which Java method implements the function =
> so I don't dare yet to write a patch. Maybe isEqualTo() ?
>

Right on the mark! See Primitives.java#L1235 and
compiler-pass2.lisp:p2-numeric-comparison ; the former for interpreted
code, the latter for compiled code.

Thanks for taking the time to submit patches!

-- 
Bye,

Erik.

http://efficito.com -- Hosted accounting and ERP.
Robust and Flexible. No vendor lock-in.
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