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
41 getbits_crc
42
43 Input
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
52 calculate_crc
53
54 Input
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
getbits_crc(tmp3Bits * inputStream,int32 neededBits,uint32 * crc,uint32 crc_enabled)123 uint32 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
calculate_crc(uint32 data,uint32 length,uint32 * crc)141 void 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