[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Nitpick with FLOOR etc.

This page is part of the web mail archives of SRFI 70 from before July 7th, 2015. The new archives for SRFI 70 are here. Eventually, the entire history will be moved there, including any new messages.



> From: Paul Schlie <schlie@xxxxxxxxxxx>
>> From: Aubrey Jaffer <agj@xxxxxxxxxxxx>
>>  | Date: Tue, 02 Aug 2005 21:48:52 -0400
>>  | From: Paul Schlie <schlie@xxxxxxxxxxx>
>>  | 
>>  | > From: Aubrey Jaffer <agj@xxxxxxxxxxxx>
>>  | >  | From: Paul Schlie <schlie@xxxxxxxxxxx>
>>  | >  |
>>  | >  | - I still don't understand how it's acceptable for (/ 1/-0.0)
>>  | >  | => 0.0, as it seems neither necessary, nor desirable to
>>  | >  | propagate IEEE-754 mistake.
>>  | > 
>>  | > (limit / -/0. -1.0e222) ==> 0.0
>>  | 
>>  | - which is only the case as you don't differentiate between -0.0
>>  |   and +0.0;
>> 
>> The `limit' procedure does not call `/' at the limit point.
>> Its last call to `+' generating the return value is
>> 
>>   (+ 999.9999999999999e-225 -999.9999999999999e-225) ==> 0.0
> 
> - Therefore it would appear the implementation of limit is flawed,
>   as if it is agreed that: #i-1/0 :: -1.0/0 :: 1/-0.0 :: -Inf.0
>   then it follows that it's reciprocal must then be correspondingly
>   both infinitesimally small and negative (not positive). Apparently
>   resulting from it's implementation not treating +-0.0 as special
>   case reciprocal infinite, as in general the magnitude of the
>   deviation about a value should never be greater than the magnitude
>   of the value itself, as otherwise the limit calculation will be
>   erroneous, where the only arguable exception would be about an
>   absolute 0, where by definition any deviation about itself will
>   result in varying signed magnitudes (where absolute 0 has neither
>   a sign nor magnitude).

- more specifically, deviations about a point should only likely be
  considered generically acceptable iff they remain within the region
  of a function's continuity; where for division this deviations of
  greater magnitude than the limit point will produce errinous results.