Hex to Bytes, ruby and java

Question

I have the following code to convert hex string to bytes in Java:

String s = "longhex";
int len = s.length();
byte[] data = new byte[(len / 2)];
for (int i = 0; i < len; i += 2)
{
    data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i + 1), 16));
}

is this a correct way to reproduce it in ruby?

s = "longhex"
bytes = []
(0..s.length / 2 - 1).step(2).each do |i|
   bytes[i / 2] = s[i].ord << 4 + s[i + 1].ord
end

I get error when I run your java code, Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 7 — Mohanraj, Sep 13 '17 at 13:02
It's becase actual string is longer `43cfde6a0996a389cd2df5a2c5bd680d44ff77534364446f96621719c4dc3f6b88ff61304ac4856e04403e0d1df446e79592c2b80352ed06c262a3a1f75bae47` — Ilya Cherevkov, Sep 13 '17 at 13:03
So, you want to convert hex string to decimal bytes, Am I correct? — Mohanraj, Sep 13 '17 at 13:08

Aleksei Matiushkin · Accepted Answer · 2017-09-13T14:53:44.213

1

No it is not correct. << has a lower operator precedence than +. Note even in java there are parentheses around shift operator. Also, it’s not ruby, it’s c written with an almost ruby syntax.

 str.codepoints.
     each_slice(2).
     map { |f, l| (f << 4) + l }

would probably do what you want, but without seeing an expected outcome it’s hard to say.

Correct version as by Ilya is:

str.scan(/.{1}/).
    each_slice(2).
    map { |f, l| (Integer(f,16) << 4) + Integer(l,16) }

edited Sep 13 '17 at 14:53

answered Sep 13 '17 at 13:12

Aleksei Matiushkin

105,980
9
87
132

I needed to edit it a bit `s.scan(/.{1}/).each_slice(2). map { |f, l| (Integer(f,16) << 4) + Integer(l,16) }` – Ilya Cherevkov Sep 13 '17 at 14:42
@IlyaCherevkov Thanks, I have updated the answer accordingly. – Aleksei Matiushkin Sep 13 '17 at 14:54

Hex to Bytes, ruby and java

1 Answers1