Re: convert byte array to hex string using BigInteger

lipska the kat <"nospam at neversurrender dot co dot uk">
Fri, 21 Jun 2013 08:17:54 +0100
On 20/06/13 21:39, Lew wrote:

lipska the kat wrote:

Laura Schmidt wrote:

rossum wrote:

This is a case of RTFM. The Javadocs for BigInteger(byte[]) tell you
that it expects the byte array in two's complement representation, so
a leading 1 bit is interpreted as a negative number. You need a
different constructor:

    public BigInteger(int signum, byte[] magnitude)

You are right, sorry.

Now I get a hex string without sign. But now the decode method does not
return the original bytes anymore:

   private byte [] hex_decode (String val)
    BigInteger b = new BigInteger (val,16);
    byte [] t = b.toByteArray();

    return (t);

There is no other constructor for byte arrays.
And I don't really understand why it doesn't return the original byte

I'm not sure what all this twos compliment stuff is about

That's spelled "two's-complement".

twos compliment is just a number representation scheme

And the purpose of that constructor is just to convert a representation
in that scheme to the correct number.

There should be no need to 'convert' anything

If there isn't, then don't use that constructor.

How incredibly interesting.


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