Scodec : Decoding Packed-Decimal

[Olivier Girardot]

Hi everyone (this is copied from the scodec mailing-list), 

I'm trying to decode packed-decimal (c.f. https://en.wikipedia.org/wiki/Binary-coded_decimal ) 

One simple example is something like that : 

   println(Codec.decode(hex"9321".bits)(uint4 ~~ uint4 ~~ uint4 ~~ uint4))

with the result being : 

   Successful(DecodeResult((9,3,2,1),BitVector(empty)))

I would like to be able to create a Codec or helper function where I can only specify the number of 4-bits, I want to parse and get the associated Long.

Like that : 

   > println(Codec.decode(hex"9321".bits)(packedDecimalCodec(4)))

   Successful(DecodeResult((9321),BitVector(empty)))

I'm kind of stuck here, and I'd really appreciate your help.

Regards, 

Olivier.

[chris...@gmail.com]

I did something similar to this here.  It differs slightly in that I'm also decoding the number of times to run a given codec from the input bytes.  If you remove the size encoding/decoding stuff, it should do what you want.

[Olivier Girardot]

Nice, Thanks !

I didn't notice the decoding context, any other snippet or examples, that I could leverage to better get my hands around this ?

Regards, 

Olivier.

[Michael Pilquist]

By the way, just last night I deprecated DecodingContext, as ever since the refactor in 1.7.0, it is completely redundant with Decoder’s flatMap method, which Codec inherits. So for example, code like this:

(for {

  a <- DecodingContext(codecA)

  b <- DecodingContext(codecB)

} yield a + b).decode(bits)

Is equivalent to:

(for {

  a <-codecA

  b <-codecB

} yield a + b).decode(bits)

Cheers,

Michael

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[chris...@gmail.com]

I learned about the decoding context from here.   Even though the decoding context is going away, apparently, you still might find it useful. Working through the 3 parts of this tutorial made working with scodec much easier for me.

[Olivier Girardot]

So to decode "n" times a uint4 

I guess I'd just need to do as much for comprehension ?