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*To*: Aubrey Jaffer <agj@xxxxxxxxxxxx>, <sperber@xxxxxxxxxxxxxxxxxxxxxxxxxxx>*Subject*: Re: Nitpick with FLOOR etc.*From*: Paul Schlie <schlie@xxxxxxxxxxx>*Date*: Sat, 16 Jul 2005 04:38:16 -0400*Cc*: <srfi-70@xxxxxxxxxxxxxxxxx>*Delivered-to*: srfi-70@xxxxxxxxxxxxxxxxx*In-reply-to*: <20050716020125.0F8911B77B4@xxxxxxxxxxxxxxxx>*User-agent*: Microsoft-Entourage/11.1.0.040913

> | From: Michael Sperber <sperber@xxxxxxxxxxxxxxxxxxxxxxxxxxx> > | Huh. I was kind of expecting you to remove the "integers" sentence. :-) > > That is also a reasonable approach. > > | What are the return values for infinities supposed to be? > > From a mathematical point of view, it seems like a slippery slope. > Often, the result of ROUND, CEILING, FLOOR, or TRUNCATE is passed to > INEXACT->EXACT. If infinities are the only non-integers allowed to be > returned from these functions, should infinities be the only inexacts > allowed to be returned from `INEXACT->EXACT'? > > | Are these procedures allowed to signal an error in those cases? > > As SRFI-70 is now I believe the answer can be yes; because infinities > are non-integers and there is no closest integer. But if an > implementation lacks inexact bignums, then there is a closest integer, > namely the largest magnitude inexacts! > > If the stipulation that inexacts args produce inexacts results takes > priority over finding the closest integer, then only inexact integers > are eligible. For an implementation having IEEE-754 64.bit flonum > inexacts: > > procedure #i-/0 #i+/0 > ========= ===== ===== > > floor error 179.76931348623157e306 > > ceiling -179.76931348623157e306 error > > truncate -179.76931348623157e306 179.76931348623157e306 > > round -179.76931348623157e306 179.76931348623157e306 - are you proposing that a run-time error must be signaled; or more reasonably only that it may, and/or alternatively return -1/0 +1/0 ? [which I tend to view as being equivalent to #i-/0, #i+/0] - what about -0/1, +0/1 ? - should (= (floor x) (/ (ceiling (/ x))) [or reasonable approximation] ?

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