1package com.googlecode.mp4parser.boxes.mp4.objectdescriptors;
2
3import java.nio.ByteBuffer;
4
5public class BitWriterBuffer {
6
7    private ByteBuffer buffer;
8    int initialPos;
9    int position = 0;
10
11    public BitWriterBuffer(ByteBuffer buffer) {
12        this.buffer = buffer;
13        this.initialPos = buffer.position();
14    }
15
16    public void writeBits(int i, int numBits) {
17        assert i <= ((1 << numBits)-1): String.format("Trying to write a value bigger (%s) than the number bits (%s) allows. " +
18                "Please mask the value before writing it and make your code is really working as intended.", i, (1<<numBits)-1);
19
20        int left = 8 - position % 8;
21        if (numBits <= left) {
22            int current = (buffer.get(initialPos + position / 8));
23            current = current < 0 ? current + 256 : current;
24            current += i << (left - numBits);
25            buffer.put(initialPos + position / 8, (byte) (current > 127 ? current - 256 : current));
26            position += numBits;
27        } else {
28            int bitsSecondWrite = numBits - left;
29            writeBits(i >> bitsSecondWrite, left);
30            writeBits(i & (1 << bitsSecondWrite) - 1, bitsSecondWrite);
31        }
32        buffer.position(initialPos + position / 8 + ((position % 8 > 0) ? 1 : 0));
33    }
34
35
36}
37