omxVCM4P2_DecodeVLCZigzag_IntraDCVLC.c revision 0c1bc742181ded4930842b46e9507372f0b1b963 
1/**
2 *
3 * File Name:  omxVCM4P2_DecodeVLCZigzag_IntraDCVLC.c
4 * OpenMAX DL: v1.0.2
5 * Revision:   9641
6 * Date:       Thursday, February 7, 2008
7 *
8 * (c) Copyright 2007-2008 ARM Limited. All Rights Reserved.
9 *
10 *
11 *
12 * Description:
13 * Contains modules for zigzag scanning and VLC decoding
14 * for intra block.
15 *
16 */
17
18#include "omxtypes.h"
19#include "armOMX.h"
20#include "omxVC.h"
21
22#include "armVC.h"
23#include "armCOMM_Bitstream.h"
24#include "armCOMM.h"
25#include "armVCM4P2_Huff_Tables_VLC.h"
26#include "armVCM4P2_ZigZag_Tables.h"
27
28
29
30
31/**
32 * Function:  omxVCM4P2_DecodeVLCZigzag_IntraDCVLC   (6.2.5.2.2)
33 *
34 * Description:
35 * Performs VLC decoding and inverse zigzag scan of AC and DC coefficients
36 * for one intra block.  Two versions of the function (DCVLC and ACVLC) are
37 * provided in order to support the two different methods of processing DC
38 * coefficients, as described in [ISO14496-2], subclause 7.4.1.4,  Intra DC
39 * Coefficient Decoding for the Case of Switched VLC Encoding.
40 *
41 * Input Arguments:
42 *
43 *   ppBitStream - pointer to the pointer to the current byte in the
44 *            bitstream buffer
45 *   pBitOffset - pointer to the bit position in the current byte referenced
46 *            by *ppBitStream.  The parameter *pBitOffset is valid in the
47 *            range [0-7].
48 *            Bit Position in one byte:  |Most      Least|
49 *                    *pBitOffset        |0 1 2 3 4 5 6 7|
50 *   predDir - AC prediction direction; used to select the zigzag scan
51 *            pattern; takes one of the following values:
52 *            -  OMX_VC_NONE - AC prediction not used;
53 *                             performs classical zigzag scan.
54 *            -  OMX_VC_HORIZONTAL - Horizontal prediction;
55 *                             performs alternate-vertical zigzag scan;
56 *            -  OMX_VC_VERTICAL - Vertical prediction;
57 *                             performs alternate-horizontal zigzag scan.
58 *   shortVideoHeader - binary flag indicating presence of
59 *            short_video_header; escape modes 0-3 are used if
60 *            shortVideoHeader==0, and escape mode 4 is used when
61 *            shortVideoHeader==1.
62 *   videoComp - video component type (luminance or chrominance) of the
63 *            current block
64 *
65 * Output Arguments:
66 *
67 *   ppBitStream - *ppBitStream is updated after the block is decoded such
68 *            that it points to the current byte in the bit stream buffer
69 *   pBitOffset - *pBitOffset is updated such that it points to the current
70 *            bit position in the byte pointed by *ppBitStream
71 *   pDst - pointer to the coefficient buffer of current block; must be
72 *            4-byte aligned.
73 *
74 * Return Value:
75 *
76 *    OMX_Sts_NoErr - no error
77 *    OMX_Sts_BadArgErr - bad arguments, if:
78 *    -    At least one of the following pointers is NULL:
79 *         ppBitStream, *ppBitStream, pBitOffset, pDst
80 *    -    *pBitOffset exceeds [0,7]
81 *    -    preDir exceeds [0,2]
82 *    -    pDst is not 4-byte aligned
83 *    OMX_Sts_Err - if:
84 *    -    In DecodeVLCZigzag_IntraDCVLC, dc_size > 12
85 *    -    At least one of mark bits equals zero
86 *    -    Illegal stream encountered; code cannot be located in VLC table
87 *    -    Forbidden code encountered in the VLC FLC table.
88 *    -    The number of coefficients is greater than 64
89 *
90 */
91
92OMXResult omxVCM4P2_DecodeVLCZigzag_IntraDCVLC(
93     const OMX_U8 ** ppBitStream,
94     OMX_INT * pBitOffset,
95     OMX_S16 * pDst,
96     OMX_U8 predDir,
97     OMX_INT shortVideoHeader,
98     OMXVCM4P2VideoComponent videoComp
99)
100{
101    /* Dummy initilaization to remove compilation error */
102    OMX_S8  DCValueSize = 0;
103    OMX_U16 powOfSize, fetchDCbits;
104    OMX_U8 start = 1;
105
106    /* Argument error checks */
107    armRetArgErrIf(ppBitStream == NULL, OMX_Sts_BadArgErr);
108    armRetArgErrIf(*ppBitStream == NULL, OMX_Sts_BadArgErr);
109    armRetArgErrIf(pBitOffset == NULL, OMX_Sts_BadArgErr);
110    armRetArgErrIf(pDst == NULL, OMX_Sts_BadArgErr);
111    armRetArgErrIf(!armIs4ByteAligned(pDst), OMX_Sts_BadArgErr);
112    armRetArgErrIf((*pBitOffset < 0) || (*pBitOffset > 7), OMX_Sts_BadArgErr);
113    armRetArgErrIf((predDir > 2), OMX_Sts_BadArgErr);
114
115    /* Insert the code into the bitstream */
116    if (videoComp == OMX_VC_LUMINANCE)
117    {
118        DCValueSize = armUnPackVLC32(ppBitStream,
119                            pBitOffset, armVCM4P2_aIntraDCLumaIndex);
120    }
121    else if (videoComp == OMX_VC_CHROMINANCE)
122    {
123        DCValueSize = armUnPackVLC32(ppBitStream,
124                            pBitOffset, armVCM4P2_aIntraDCChromaIndex);
125    }
126    armRetDataErrIf(DCValueSize == -1, OMX_Sts_Err);
127    armRetDataErrIf(DCValueSize > 12, OMX_Sts_Err);
128
129
130    if (DCValueSize == 0)
131    {
132        pDst[0] = 0;
133    }
134    else
135    {
136        fetchDCbits = (OMX_U16) armGetBits(ppBitStream, pBitOffset, \
137                                           DCValueSize);
138
139        if ( (fetchDCbits >> (DCValueSize - 1)) == 0)
140        {
141            /* calulate pow */
142            powOfSize = (1 << DCValueSize);
143
144            pDst[0] =  (OMX_S16) (fetchDCbits ^ (powOfSize - 1));
145            pDst[0] = -pDst[0];
146        }
147        else
148        {
149            pDst[0] = fetchDCbits;
150        }
151
152        if (DCValueSize > 8)
153        {
154            /* reading and checking the marker bit*/
155            armRetDataErrIf (armGetBits(ppBitStream, pBitOffset, 1) == 0, \
156                             OMX_Sts_Err);
157        }
158    }
159
160    return armVCM4P2_DecodeVLCZigzag_Intra(
161                ppBitStream,
162                pBitOffset,
163                pDst,
164                predDir,
165                shortVideoHeader,
166                start);
167}
168
169/* End of file */
170
171