将有符号字节转换为无符号半字节

Question

So I have asmall problem here, and I have no clue what could be wrong. Thats why I'm asking if this (what I'll show you now) ist correct. I'm turning Binary Files into Byte Lists, so that I can turn those bytes into half bytes. For Example: If I get 96 as decimal number (60 as hexadecimal) I want to get 6 and 0 out of it. The same thing with 127 (hex:7F) - I want to get 7 and 15. To achieve this I wrote the following code: You'll notice, that I need "unsigned bytes" for this in order to work

System.out.println((byte) ((UnsignedByte.unsignedToBytes(b) - (UnsignedByte.unsignedToBytes(b) % 16)) / 16));
System.out.println((byte) (UnsignedByte.unsignedToBytes(b) % 16));

public static int unsignedToBytes(byte b) {
    return b & 0xFF;
}

Am I doing something wrong or is this not a Problem?

Answer 1

Use bit shifting and bitwise operations:

• To get the lower four bits, use lowerNibble = wholeByte & 0x0F
• To get the upper four bits, use upperNibble = (wholeByte >> 4) & 0x0F

This disregards the sign, because the upper portion of the number is truncated off by & 0x0F .