1/* ------------------------------------------------------------------
2 * Copyright (C) 1998-2009 PacketVideo
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
13 * express or implied.
14 * See the License for the specific language governing permissions
15 * and limitations under the License.
16 * -------------------------------------------------------------------
17 */
18/*
19------------------------------------------------------------------------------
20
21   PacketVideo Corp.
22   MP3 Decoder Library
23
24   Filename: pvmp3_crc.cpp
25
26   Functions:
27        getbits_crc
28        calculate_crc
29
30     Date: 09/21/2007
31
32------------------------------------------------------------------------------
33 REVISION HISTORY
34
35
36 Description:
37
38------------------------------------------------------------------------------
39 INPUT AND OUTPUT DEFINITIONS
40
41getbits_crc
42
43Input
44    tbits *inputStream,     bit stream structure
45    int32 neededBits,       number of bits to read from the bit stream
46    uint32 *crc,            memory location holding calculated crc value
47    uint32 crc_enabled      flag to enable/disable crc checking
48
49------------------------------------------------------------------------------
50 INPUT AND OUTPUT DEFINITIONS
51
52calculate_crc
53
54Input
55    uint32 data,            data vector
56    uint32 length,          number of element upon the crc will be calculated
57    uint32 *crc,            memory location holding calculated crc value
58
59------------------------------------------------------------------------------
60 FUNCTION DESCRIPTION
61
62
63------------------------------------------------------------------------------
64 REQUIREMENTS
65
66
67------------------------------------------------------------------------------
68 REFERENCES
69
70 [1] ISO MPEG Audio Subgroup Software Simulation Group (1996)
71     ISO 13818-3 MPEG-2 Audio Decoder - Lower Sampling Frequency Extension
72
73------------------------------------------------------------------------------
74 PSEUDO-CODE
75
76 ------------------------------------------------------------------------------
77*/
78
79
80/*----------------------------------------------------------------------------
81; INCLUDES
82----------------------------------------------------------------------------*/
83
84#include "pvmp3_getbits.h"
85#include "pvmp3_crc.h"
86
87/*----------------------------------------------------------------------------
88; MACROS
89; Define module specific macros here
90----------------------------------------------------------------------------*/
91
92
93/*----------------------------------------------------------------------------
94; DEFINES
95; Include all pre-processor statements here. Include conditional
96; compile variables also.
97----------------------------------------------------------------------------*/
98
99/*----------------------------------------------------------------------------
100; LOCAL FUNCTION DEFINITIONS
101; Function Prototype declaration
102----------------------------------------------------------------------------*/
103
104/*----------------------------------------------------------------------------
105; LOCAL STORE/BUFFER/POINTER DEFINITIONS
106; Variable declaration - defined here and used outside this module
107----------------------------------------------------------------------------*/
108
109/*----------------------------------------------------------------------------
110; EXTERNAL FUNCTION REFERENCES
111; Declare functions defined elsewhere and referenced in this module
112----------------------------------------------------------------------------*/
113
114/*----------------------------------------------------------------------------
115; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES
116; Declare variables used in this module but defined elsewhere
117----------------------------------------------------------------------------*/
118
119/*----------------------------------------------------------------------------
120; FUNCTION CODE
121----------------------------------------------------------------------------*/
122
123uint32 getbits_crc(tmp3Bits *inputStream,  /* bit stream structure */
124                   int32 neededBits, /* number of bits to read from the bit stream */
125                   uint32 *crc,
126                   uint32 crc_enabled)
127{
128    uint32 bits = getNbits(inputStream, neededBits);
129
130    if (crc_enabled)
131    {
132        calculate_crc(bits, neededBits, crc);
133    }
134    return(bits);
135}
136
137/*----------------------------------------------------------------------------
138; FUNCTION CODE
139----------------------------------------------------------------------------*/
140
141void calculate_crc(uint32 data,
142                   uint32 length,
143                   uint32 *crc)
144{
145    uint32  carry;
146    uint32  masking = 1 << length;
147
148    while ((masking >>= 1))
149    {
150        carry = *crc & 0x8000;
151        *crc <<= 1;
152        if (!carry ^ !(data & masking))
153        {
154            *crc ^= CRC16_POLYNOMIAL;
155        }
156    }
157    *crc &= 0xffff;
158}
159
160
161
162