I've checked with a python repl, the correct value seems to be the one
using BigDecs
>>> from decimal import *
>>> Decimal('1.4411518807585587E17') / Decimal(2)
Decimal('72057594037927935')
I've submitted a bug and commented on it about BigDecimal constructors
but I may have made a mistake about which value is the correct one...
Bye,
Laurent
On 1 juin, 19:21, Tassilo Horn <tass...@member.fsf.org> wrote:
> kawas <laurent.joi...@gmail.com> writes:
>
> Hi Laurent,
>
> > (defn prime-factors [n]
> > (loop [f 2 n n res []]
> > (cond
> > (<= n 1) res
> > (zero? (rem n f)) (recur f (quot n f) (conj res f))
> > :else (recur (inc f) n res))))
>
> > Problem 1 (solved): If you use (= n 1) in the first cond clause, the
> > function may not terminate because (= 1 1.0) may be false. But we all
> > know that :)
>
> Use (== n 1) instead.
>
> > Problem 2: Now compare theses function calls
> > (prime-factors (Math/pow 2 58))
> > (prime-factors (bigdec (Math/pow 2 58)))
> > (prime-factors (bigint (bigdec (Math/pow 2 58))))
>
> > The last two function calls are really really slow.
> > - Is this only a problem of rem/quot slow on big numbers ?
>
> No, debugging it a bit it seems to be a bug in
> clojure.lang.Numbers.quotient() applied to BigDecs:
>
> user> (quot 1.4411518807585587E17 2) ;; correct with doubles
> 7.2057594037927936E16
> user> (quot 1.4411518807585587E+17M 2) ;; wrong with BigDecs
> 72057594037927935M
>
> Please file a bug report about that.
>
> Bye,
> Tassilo
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