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POClojure BigInt is not Java BigInteger
 

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    <p>I'm trying to use BigDecimals in Clojure to model (if necessary) arbitrary precision numbers. I have a strange error when I try to instantiate a BigDecimal from an unscaled value and scale factor:</p> <pre><code>user=&gt; 1.31M 1.31M (OK) user=&gt; (class 1.31M) java.math.BigDecimal (OK) user=&gt; (.unscaledValue 1.31M) 131 (OK) user=&gt; (.scale 1.31M) 2 (OK) user=&gt; (.movePointLeft (BigDecimal. 131) 2) 1.31M (OK) user=&gt; (BigDecimal. (BigInteger. "131") 2) 1.31M user=&gt; (BigDecimal. 131N 2) (WRONG!!!) IllegalArgumentException No matching ctor found for class java.math.BigDecimal clojure.lang.Reflector.invokeConstructor (Reflector.java:183) user=&gt; (BigDecimal. (BigInteger. "131") 2) 1.31M </code></pre> <p>The problem here is that the clojure big integer IS NOT a java.math.BigInteger object. Even (bigint x) doesn't work:</p> <pre><code>user=&gt; (doc bigint) ------------------------- clojure.core/bigint ([x]) Coerce to BigInt nil </code></pre> <p>And by the way BigInteger constructor doesn't directly accept numeric values. I know I could also do something like:</p> <pre><code>user=&gt; (BigDecimal. (BigInteger. (.toByteArray (.unscaledValue 1.31M))) (.scale 1.31M)) 1.31M </code></pre> <p>My question is: is there a more idiomatic way of directly manage BigInteger objects from Clojure? Or am I stuck to wrap everything in a custom library, like:</p> <pre><code>user=&gt; (defn my-bigint [x] (BigInteger. (.toString x))) #'user/my-bigint user=&gt; (my-bigint 131) 131 user=&gt; (BigDecimal. (my-bigint 131) 2) 1.31M </code></pre> <p>Thanks in advance for the help!</p> <p>UPDATE: I <strong>NEED</strong> a BigInteger for serialization purposes: my idea is to store a BigDecimal as a byte array and an integer. My problem is that in Clojure, if I want, I cannot pass the result of .unscaledValue back and forth 'cause Clojure doesn't handle BigInteger created from Integers (neither do Java, for what it matters): </p> <pre><code>user=&gt; (BigInteger. 3) IllegalArgumentException No matching ctor found for class java.math.BigInteger clojure.lang.Reflector.invokeConstructor (Reflector.java:183) </code></pre> <p>A call to .toString on the number is unuseful for the semantics of serialization (and more error prone). I would like to know if in Clojure there is an idiomatic way to write something like:</p> <pre><code>user=&gt; (bigdec 131N 2) </code></pre> <p>No .movePointLeft (creation of two different objects without benefits), no .toString (I have a number, I stringify it and then create a BigInteger, another number, from it?), no slow and indirect method: just plain BigInteger and scale value.</p> <p>Vinz</p>
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    1. USVincenzo Maggio
    1. USVincenzo Maggio
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    1. COwrap a function with bigdec source.
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    2. COIndeed my thought at the moment was to submit a patch that slighty modifies the clojure source to accept scale factor (which is the main problem). If you put this (the scale factor problem and the source code to be modified) I'll accept your answer :) (BTW, I'm starting to think this is a limitation of Java API, but it's another topic...)
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    3. COAccepted anyway, in the end your idea of bypassing BigInteger is not that bad, I'll wrap my head around it!
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