1 /*
2  * Copyright 2015, The Android Open Source Project
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 #define LOG_TAG "AudioSPDIF"
18 //#define LOG_NDEBUG 0
19 
20 #include <string.h>
21 #include <assert.h>
22 
23 #include <utils/Log.h>
24 #include "BitFieldParser.h"
25 
26 namespace android {
27 
BitFieldParser(uint8_t * data)28 BitFieldParser::BitFieldParser(uint8_t *data)
29  : mData(data)
30  , mBitCursor(0)
31 {
32 }
33 
~BitFieldParser()34 BitFieldParser::~BitFieldParser()
35 {
36 }
37 
readBits(uint32_t numBits)38 uint32_t BitFieldParser::readBits(uint32_t numBits)
39 {
40     ALOG_ASSERT(numBits <= 32);
41 
42     // Extract some bits from the current byte.
43     uint32_t byteCursor = mBitCursor >> 3; // 8 bits per byte
44     uint8_t byte = mData[byteCursor];
45 
46     uint32_t bitsLeftInByte = 8 - (mBitCursor & 7);
47     uint32_t bitsFromByte = (bitsLeftInByte < numBits) ? bitsLeftInByte : numBits;
48     uint32_t result = byte >> (bitsLeftInByte - bitsFromByte);
49     result &= (1 << bitsFromByte) - 1; // mask
50     mBitCursor += bitsFromByte;
51 
52     uint32_t bitsRemaining = numBits - bitsFromByte;
53     if (bitsRemaining == 0) {
54         return result;
55     } else {
56         // Use recursion to get remaining bits.
57         return (result << bitsRemaining) | readBits(bitsRemaining);
58     }
59 }
60 
61 }  // namespace android
62