On Tue, Jun 26, 2012 at 1:11 AM, Sean Corfield <seancorfi...@gmail.com> wrote:
> On Mon, Jun 25, 2012 at 9:19 PM, Cedric Greevey <cgree...@gmail.com> wrote:
>> user=> 1e309
>> Infinity
>
> FWIW, on 1.4.0 I get:
>
> user=> 1e309
> CompilerException java.lang.RuntimeException: Unable to resolve
> symbol: Infinity in this context, compiling:(NO_SOURCE_PATH:1)
That's *really* broken.
Unfortunately, digging deeper I found that the 1023 exponent limit is
2^1023, not 10^1023, which means it really is around 309. I've had to
reimplement some stuff using BigDecimals and to write these, since
there seem to be no corresponding methods built into Java anywhere:
(defn log [x]
(if (instance? BigDecimal x)
(let [s (.scale x)]
(+ (Math/log (.scaleByPowerOfTen x s)) (* (- s) (Math/log 10.0))))
(Math/log x)))
(defn log10 [x]
(/ (log x) (Math/log 10.0)))
(defn exp [x]
(let [r (Math/exp x)]
(if (.isInfinite r)
(let [p10 (int (/ x (Math/log 10.0)))]
(.scaleByPowerOfTen (bigdec (Math/exp (- x (* p10 (Math/log
10.0))))) p10))
r)))
These seem to work fine, where extended precision isn't really needed,
only large exponents. However, I've run into another problem, which is
that when doubles and BigDecimals mix 1.3 seems to convert to doubles.
This appears to contradict part of
http://dev.clojure.org/display/doc/Documentation+for+1.3+Numerics
specifically "When different types of numbers are used in a math
operation, the result will be the larger or more general of the two
types."
That doesn't seem to hold when the types are double and BigDecimal,
for some reason. Is there any setting I can change (analogous to
with-precision) to force BigDecimal contagion? I considered using
those icky primed operators, but for some reason /' seems to be
missing from the set and I need division...
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