bitbuffer.h revision 41050cdb033641ddf26831d9272c0930f7b40a2d 
1/*
2 ** Copyright 2003-2010, VisualOn, Inc.
3 **
4 ** Licensed under the Apache License, Version 2.0 (the "License");
5 ** you may not use this file except in compliance with the License.
6 ** You may obtain a copy of the License at
7 **
8 **     http://www.apache.org/licenses/LICENSE-2.0
9 **
10 ** Unless required by applicable law or agreed to in writing, software
11 ** distributed under the License is distributed on an "AS IS" BASIS,
12 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 ** See the License for the specific language governing permissions and
14 ** limitations under the License.
15 */
16/*******************************************************************************
17	File:		bitbuffer.h
18
19	Content:	Bit Buffer Management structure and functions
20
21*******************************************************************************/
22
23#ifndef BITBUFFER_H
24#define BITBUFFER_H
25
26#include "typedef.h"
27
28
29enum direction
30{
31  forwardDirection,
32  backwardDirection
33};
34
35
36/*!
37   The pointer 'pReadNext' points to the next available word, where bits can be read from. The pointer
38   'pWriteNext' points to the next available word, where bits can be written to. The pointer pBitBufBase
39   points to the start of the bitstream buffer and the pointer pBitBufEnd points to the end of the bitstream
40   buffer. The two pointers are used as lower-bound respectively upper-bound address for the modulo addressing
41   mode.
42
43   The element cntBits contains the currently available bits in the bit buffer. It will be incremented when
44   bits are written to the bitstream buffer and decremented when bits are read from the bitstream buffer.
45*/
46struct BIT_BUF
47{
48  UWord8 *pBitBufBase;          /*!< pointer points to first position in bitstream buffer */
49  UWord8 *pBitBufEnd;           /*!< pointer points to last position in bitstream buffer */
50
51  UWord8 *pWriteNext;           /*!< pointer points to next available word in bitstream buffer to write */
52
53  UWord32 cache;
54
55  Word16  wBitPos;              /*!< 31<=wBitPos<=0*/
56  Word16  cntBits;              /*!< number of available bits in the bitstream buffer
57                                     write bits to bitstream buffer  => increment cntBits
58                                     read bits from bitstream buffer => decrement cntBits */
59  Word16  size;                 /*!< size of bitbuffer in bits */
60  Word16  isValid;              /*!< indicates whether the instance has been initialized */
61}; /* size Word16: 8 */
62
63/*! Define pointer to bit buffer structure */
64typedef struct BIT_BUF *HANDLE_BIT_BUF;
65
66
67HANDLE_BIT_BUF CreateBitBuffer(HANDLE_BIT_BUF hBitBuf,
68                               UWord8 *pBitBufBase,
69                               Word16  bitBufSize);
70
71
72void DeleteBitBuffer(HANDLE_BIT_BUF *hBitBuf);
73
74
75Word16 GetBitsAvail(HANDLE_BIT_BUF hBitBuf);
76
77
78Word16 WriteBits(HANDLE_BIT_BUF hBitBuf,
79                 Word32 writeValue,
80                 Word16 noBitsToWrite);
81
82void ResetBitBuf(HANDLE_BIT_BUF hBitBuf,
83                 UWord8 *pBitBufBase,
84                 Word16  bitBufSize);
85
86#define GetNrBitsAvailable(hBitBuf) ( (hBitBuf)->cntBits)
87#define GetNrBitsRead(hBitBuf)       ((hBitBuf)->size-(hBitBuf)->cntBits)
88
89#endif /* BITBUFFER_H */
90