[英]Combine 4 bytes into one in Java
Here is the code: 这是代码:
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Map;
public class Shiftcodes {
private Map<byte[], Byte> shiftMap;
public byte genoByte(byte b1, byte b2, byte b3, byte b4) {
return (byte) (
(b1 << 6)
| (b2 << 4)
| (b3 << 2)
| b4);
}
public static void main(String[] args) throws IOException {
Shiftcodes shiftcodes = new Shiftcodes();
byte b = shiftcodes.genoByte((byte) 0x01, (byte) 0x11, (byte) 0x00, (byte) 0x10);
FileOutputStream fileOutputStream = new FileOutputStream("/tmp/x.bin");
fileOutputStream.write(new byte[] {b});
}
}
It's assumed that the bits of each byte are all zero, except the rightmost two bits, which can be 0 or 1. So I changed the code a little: 假定每个字节的位都为零,除了最右边的两位可以为0或1。因此,我对代码进行了一些更改:
public class Shiftcodes {
private Map<byte[], Byte> shiftMap;
public byte genoByte(byte b1, byte b2, byte b3, byte b4) {
return (byte) (
((b1 & 0x11) << 6)
| ((b2 & 0x11) << 4)
| ((b3 & 0x11) << 2)
| b4);
}
public static void main(String[] args) throws IOException {
Shiftcodes shiftcodes = new Shiftcodes();
byte b = shiftcodes.genoByte((byte) 0x01, (byte) 0x11, (byte) 0x00, (byte) 0x10);
FileOutputStream fileOutputStream = new FileOutputStream("/tmp/x.bin");
fileOutputStream.write(new byte[] {b});
}
}
But in both cases I am getting what I expected (01110010): 但是在两种情况下,我都达到了我的期望(01110010):
xxd -b x.bin
0000000: 01010000 P
Why? 为什么?
The rightmost two bits would be 0x3
not 0x11
. 最右边的两位将是
0x3
而不是0x11
。 0x11
is 00010001 in binary rather than 00000011. 0x11
二进制0x11
是00010001,而不是00000011。
return (byte) (
((b1 & 0x3) << 6)
| ((b2 & 0x3) << 4)
| ((b3 & 0x3) << 2)
| b4);
You mistake hex literals
for binary literals
: 您将
hex literals
误认为是binary literals
:
0x11; // Hex 11, Dec 17, Bits 00010001
0b11; // Hex 3, Dec 3, Bits 00000011
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