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Re: Help with BCD conversion

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 Roedy Green wrote:
> The original IBM 360 style packed two decimal digits per nibble into
> an 8 bit byte. It was stored big-endian. The last nibble encoded the

That's BCD packed. There's also BCD unpacked.

> sign, using one of the hex digits A-F. A, C, E, and F indicate
> positive values, and B and D indicate negative values. Seems to me C,
> D and F were preferred.
> 
> IIRC there was no explicit length encoding.  That was either
> determined in the instruction code or by banging into the sign nibble.

There's no explicit length encoding in Java's 'BigDecimal' either. There's 
no reason to expect one.

> If there were an even number of digits, it was padded out with a left
> zero.
> 
> OP wants to simulate this on Java without the sign.  It could be done
> with a String, left zero padded to an even number of digits, which is
> a trivial problem. It could be done with a byte array, two digits per
> byte. The end result could be an int or long. You could start with a
> String, int or long.  I wanted OP to be aware of the possible choices
> and pick the best for his purposes before nailing down code.
> 
> This nibble packing is very similar to converting a Hex string to an
> int. 
> 
> The core packing code is something like this
> int lowNibble = ...
> int highNibble = ...
> int combinedbyte = highNibble << 8 | lowNibble;
> 
> You probably don't want to use the byte type because it sign extends.
> I have yet to find a need for signed bytes.  I wish Java had made
> bytes unsigned. It would have saved so many hair follicles.

That's not a reason not to use the byte type. You just have to compensate 
for it. Don't throw the baby out with the bath water.

> The code OP presented with case clauses is fundamentally incorrect in
> that it treats each of the cases as different. They are not, and
> should be handled by the same code.I think that is mainly why everyone
> has been reluctant to delve into it.

Amen to that.

-- 
Lew

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Thread

Help with BCD conversion HarishD <harishdeshpande@gmail.com> - 2012-02-17 15:21 -0800
  Re: Help with BCD conversion Roedy Green <see_website@mindprod.com.invalid> - 2012-02-17 15:33 -0800
    Re: Help with BCD conversion HarishD <harishdeshpande@gmail.com> - 2012-02-17 15:39 -0800
    Re: Help with BCD conversion HarishD <harishdeshpande@gmail.com> - 2012-02-17 15:47 -0800
      Re: Help with BCD conversion markspace <-@.> - 2012-02-18 08:24 -0800
        Re: Help with BCD conversion Roedy Green <see_website@mindprod.com.invalid> - 2012-02-18 09:06 -0800
          Re: Help with BCD conversion Lew <lewbloch@gmail.com> - 2012-02-18 10:25 -0800
            Re: Help with BCD conversion HarishD <harishdeshpande@gmail.com> - 2012-02-20 06:35 -0800
              Re: Help with BCD conversion Lew <noone@lewscanon.com> - 2012-02-20 11:52 -0800
        Re: Help with BCD conversion Lew <lewbloch@gmail.com> - 2012-02-18 10:21 -0800

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