[GitHub] [avro] ziggythehamster edited a comment on pull request #840: [AVRO-2677] Added decimal encoding and decoding logic

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ziggythehamster edited a comment on pull request #840:
URL: https://github.com/apache/avro/pull/840#issuecomment-640154458


   Here's the Java decoder: https://github.com/apache/avro/blob/93ec41bacf678a875d3696dec72a84901482602a/lang/java/avro/src/main/java/org/apache/avro/Conversions.java#L82-L88
   
   and the Java encoder: https://github.com/apache/avro/blob/93ec41bacf678a875d3696dec72a84901482602a/lang/java/avro/src/main/java/org/apache/avro/Conversions.java#L90-L95
   
   and since I'm not a Java programmer, I looked at the docs for Java BigDecimal and see this statement:
   
   > The value of the number represented by the BigDecimal is therefore (unscaledValue × 10-scale).
   
   Excellent, because Ruby's [BigDecimal#split](https://ruby-doc.org/stdlib-2.7.1/libdoc/bigdecimal/rdoc/BigDecimal.html#method-i-split) method will give you the significant digits and exponent which I think is the same.
   
   Of course, you now need to figure out what Java's BigInteger `toByteArray` is doing exactly, and [here's the docs for that](https://docs.oracle.com/javase/8/docs/api/java/math/BigInteger.html#toByteArray--). Almost a decade ago, someone on Stack Overflow worked on a [version of this](https://stackoverflow.com/questions/5284369/ruby-return-byte-array-containing-twos-complement-representation-of-bignum-fi)... and it's been longer than that since I took any CS classes, so hopefully someone with a bit more freshness there can take this information and run with it :).
   
   Finally, once you've got the array of integers, you'll need to use [Array#pack](https://ruby-doc.org/core-2.7.1/Array.html#method-i-pack) to make it a string. I think you need the pattern `C*`.


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