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      1 /*
      2  * Copyright (C) 2010 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 #include "ABitReader.h"
     18 
     19 #include <media/stagefright/foundation/ADebug.h>
     20 
     21 namespace android {
     22 
     23 ABitReader::ABitReader(const uint8_t *data, size_t size)
     24     : mData(data),
     25       mSize(size),
     26       mReservoir(0),
     27       mNumBitsLeft(0) {
     28 }
     29 
     30 ABitReader::~ABitReader() {
     31 }
     32 
     33 void ABitReader::fillReservoir() {
     34     CHECK_GT(mSize, 0u);
     35 
     36     mReservoir = 0;
     37     size_t i;
     38     for (i = 0; mSize > 0 && i < 4; ++i) {
     39         mReservoir = (mReservoir << 8) | *mData;
     40 
     41         ++mData;
     42         --mSize;
     43     }
     44 
     45     mNumBitsLeft = 8 * i;
     46     mReservoir <<= 32 - mNumBitsLeft;
     47 }
     48 
     49 uint32_t ABitReader::getBits(size_t n) {
     50     CHECK_LE(n, 32u);
     51 
     52     uint32_t result = 0;
     53     while (n > 0) {
     54         if (mNumBitsLeft == 0) {
     55             fillReservoir();
     56         }
     57 
     58         size_t m = n;
     59         if (m > mNumBitsLeft) {
     60             m = mNumBitsLeft;
     61         }
     62 
     63         result = (result << m) | (mReservoir >> (32 - m));
     64         mReservoir <<= m;
     65         mNumBitsLeft -= m;
     66 
     67         n -= m;
     68     }
     69 
     70     return result;
     71 }
     72 
     73 void ABitReader::skipBits(size_t n) {
     74     while (n > 32) {
     75         getBits(32);
     76         n -= 32;
     77     }
     78 
     79     if (n > 0) {
     80         getBits(n);
     81     }
     82 }
     83 
     84 void ABitReader::putBits(uint32_t x, size_t n) {
     85     CHECK_LE(n, 32u);
     86 
     87     while (mNumBitsLeft + n > 32) {
     88         mNumBitsLeft -= 8;
     89         --mData;
     90         ++mSize;
     91     }
     92 
     93     mReservoir = (mReservoir >> n) | (x << (32 - n));
     94     mNumBitsLeft += n;
     95 }
     96 
     97 size_t ABitReader::numBitsLeft() const {
     98     return mSize * 8 + mNumBitsLeft;
     99 }
    100 
    101 const uint8_t *ABitReader::data() const {
    102     return mData - (mNumBitsLeft + 7) / 8;
    103 }
    104 
    105 NALBitReader::NALBitReader(const uint8_t *data, size_t size)
    106     : ABitReader(data, size),
    107       mNumZeros(0) {
    108 }
    109 
    110 bool NALBitReader::atLeastNumBitsLeft(size_t n) const {
    111     // check against raw size and reservoir bits first
    112     size_t numBits = numBitsLeft();
    113     if (n > numBits) {
    114         return false;
    115     }
    116 
    117     ssize_t numBitsRemaining = n - mNumBitsLeft;
    118 
    119     size_t size = mSize;
    120     const uint8_t *data = mData;
    121     int32_t numZeros = mNumZeros;
    122     while (size > 0 && numBitsRemaining > 0) {
    123         bool isEmulationPreventionByte = (numZeros >= 2 && *data == 3);
    124 
    125         if (*data == 0) {
    126             ++numZeros;
    127         } else {
    128             numZeros = 0;
    129         }
    130 
    131         if (!isEmulationPreventionByte) {
    132             numBitsRemaining -= 8;
    133         }
    134 
    135         ++data;
    136         --size;
    137     }
    138 
    139     return (numBitsRemaining <= 0);
    140 }
    141 
    142 void NALBitReader::fillReservoir() {
    143     CHECK_GT(mSize, 0u);
    144 
    145     mReservoir = 0;
    146     size_t i = 0;
    147     while (mSize > 0 && i < 4) {
    148         bool isEmulationPreventionByte = (mNumZeros >= 2 && *mData == 3);
    149 
    150         if (*mData == 0) {
    151             ++mNumZeros;
    152         } else {
    153             mNumZeros = 0;
    154         }
    155 
    156         // skip emulation_prevention_three_byte
    157         if (!isEmulationPreventionByte) {
    158             mReservoir = (mReservoir << 8) | *mData;
    159             ++i;
    160         }
    161 
    162         ++mData;
    163         --mSize;
    164     }
    165 
    166     mNumBitsLeft = 8 * i;
    167     mReservoir <<= 32 - mNumBitsLeft;
    168 }
    169 
    170 }  // namespace android
    171