How to convert 160 digit binary string to 20 byte array?

Question

I have a binary string containing 160 digit. I have tried:

new BigInteger("0000000000000000000000000000000000000000000000010000000000000000000000000000001000000000010000011010000000000000000000000000000000000000000000000000000000000000", 2).toByteArray()

but it returns the 15 bytes array with removed leading 0 bytes.

I would like reserve those leading 0 bytes, keep it 20 bytes.

I know some other ways to accomplish that, but I would like to know is there any easier way might just need few lines of code.

You can extend your array by `8-currentSize` elements with value = 0 on the left side — sasha.sochka, Jul 11 '13 at 07:42
@anubhava It's implied by OP's line of code: `binStr = "0011010111...11"; array = {120, -145, ..., 20}`. — Marko Topolnik, Jul 11 '13 at 07:52
You still can't store 160 bits in 8 bytes - you need 20 bytes. — Ingo, Jul 11 '13 at 07:52
You could use System.arraycopy to copy to copy to 8 byte array — Bruce Martin, Jul 11 '13 at 07:57
8 bytes only hold 64 bits, as @Ingo said you need 20 bytes for 160 bits. — Christoffer Hammarström, Jul 11 '13 at 08:25
Here is the binStr 0000000000000000000000000000000000000000000000010000000000000000000000000000001000000000010000011010000000000000000000000000000000000000000000000000000000000000 — Arst, Jul 11 '13 at 09:44

Ingo · Answer 1 · 2013-07-11T08:23:58.060

1

Why not simply:

public static byte[] convert160bitsToBytes(String binStr) {
    byte[] a = new BigInteger(binStr, 2).toByteArray();
    byte[] b = new byte[20];
    int i = 20 - a.length;
    int j = 0;
    if (i < 0) throw new IllegalArgumentException("string was too long");
    for (; j < a.length; j++,i++) {
        b[i] = a[j];
    }
    return b;
}

edited Jul 11 '13 at 08:23

answered Jul 11 '13 at 08:01

Ingo

36,037
5
53
100

score 1 · Answer 2 · answered Jul 11 '13 at 10:05

Something like this code should work for you:

byte[] src = new BigInteger(binStr, 2).toByteArray();
byte[] dest = new byte[(binStr.length()+7)/8]; // 20 bytes long for String of 160 length
System.arraycopy(src, 0, dest, 20 - src.length, src.length);
// testing
System.out.printf("Bytes: %d:%s%n", dest.length, Arrays.toString(dest));

OUTPUT:

Bytes: 20:[0, 0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 65, -96, 0, 0, 0, 0, 0, 0, 0]

How to convert 160 digit binary string to 20 byte array?

2 Answers2