/* 有關(guān)比特流的操作 */

/* Heavily modified since it is now only used to write bits to a buffer. */

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "bitstream.h"		/* bit stream module */
#include "common.h"		/* common module */


#define BYTE_NUMBIT 8		/* bits in byte (char) */
#define LONG_NUMBIT 32		/* bits in unsigned long */
#define bit2byte(a) (((a)+BYTE_NUMBIT-1)/BYTE_NUMBIT)
#define byte2bit(a) ((a)*BYTE_NUMBIT)


BsBitStream *BsOpenWrite(int size)
{
	BsBitStream *bs;

	bs = malloc(sizeof(BsBitStream));
	bs->size = size;
	bs->numBit = 0;
	bs->currentBit = 0;
	bs->data = malloc(bit2byte(size));

	return bs;
}

void BsClose(BsBitStream *bs)
{
	free(bs->data);
	free(bs);
}

long BsBufferNumBit (BsBitStream *bs)
{
	return bs->numBit;
}

int BsWriteByte (BsBitStream *stream,
				 unsigned long data,
				 int numBit)
{
	long numUsed,idx;

	idx = (stream->currentBit / BYTE_NUMBIT) % bit2byte(stream->size);
	numUsed = stream->currentBit % BYTE_NUMBIT;
	if (numUsed == 0)
		stream->data[idx] = 0;
	stream->data[idx] |= (data & ((1<<numBit)-1)) <<
		BYTE_NUMBIT-numUsed-numBit;
	stream->currentBit += numBit;
	stream->numBit = stream->currentBit;

	return 0;
}

int BsPutBit (BsBitStream *stream,
			  unsigned long data,
			  int numBit)
{
	int num,maxNum,curNum;
	unsigned long bits;

	if (numBit == 0)
		return 0;

	/* write bits in packets according to buffer byte boundaries */
	num = 0;
	maxNum = BYTE_NUMBIT - stream->currentBit % BYTE_NUMBIT;
	while (num < numBit) {
		curNum = min(numBit-num,maxNum);
		bits = data>>numBit-num-curNum;
		if (BsWriteByte(stream,bits,curNum)) {
			return 1;
		}
		num += curNum;
		maxNum = BYTE_NUMBIT;
	}

	return 0;
}