x265-1.7版本-encoder/bitcost.cpp注释

注：问号以及未注释部分 会在x265-1.8版本内更新

/*****************************************************************************
 * Copyright (C) 2013 x265 project
 *
 * Authors: Steve Borho <steve@borho.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02111, USA.
 *
 * This program is also available under a commercial proprietary license.
 * For more information, contact us at license @ x265.com.
 *****************************************************************************/

#include "common.h"
#include "primitives.h"
#include "bitcost.h"

using namespace x265;
/** 函数功能             ：建立当前qp下的MVD占用的cost：λ*bits = 2^(qp/6-2) * s_bitsizes[i]
* \参数 qp               ：当前ME下的qp大小
* \返回                  ：null * */
void BitCost::setQP(unsigned int qp)
{
    if (!s_costs[qp])                  //如果当前还没有申请空间并初始化，在下面将其申请空间并初始化 s_costs,所有的me共有，每个qp只初始化一次
    {
        ScopedLock s(s_costCalcLock);  //加锁防止多线程读取脏数据

        // Now that we have acquired the lock, check again if another thread calculated
        // this row while we were blocked
        if (!s_costs[qp])
        {
            x265_emms(); // just to be safe 清除MMX寄存器中的内容，即初始化（以避免和浮点数操作发生冲突）。

            CalculateLogs(); //建立MVD估计占用bits表格,例如：当前MV.x = 3 ,则其占用bits 为 s_bitsizes[3] 2*(log2(3+1))+e-1
            s_costs[qp] = new uint16_t[4 * BC_MAX_MV + 1] + 2 * BC_MAX_MV;  //申请空间为4*32768+1  并指向当前地址2*32768
            double lambda = x265_lambda_tab[qp];  //2^(qp/6-2)

            // estimate same cost for negative and positive MVD
            for (int i = 0; i <= 2 * BC_MAX_MV; i++)
                s_costs[qp][i] = s_costs[qp][-i] = (uint16_t)X265_MIN(s_bitsizes[i] * lambda + 0.5f, (1 << 16) - 1);//其值为 s_bitsizes[i] * lambda  四舍五入取整
        }
    }

    m_cost = s_costs[qp];   //将m_cost指针指向当前qp所对应的MVD cost表（MVD为0的位置），在计算MVD的cost就是通过MVD寻址m_cost表
                            //在setMVP()中，将m_cost_mvx/m_cost_mvy赋值为MVP的cost表地址，在ME中根据MVD来寻址m_cost_mvx/m_cost_mvy，即可以得到mvx/mvy的cost
}

/***
 * Class static data and methods
 */

uint16_t *BitCost::s_costs[BC_MAX_QP]; //所有的me共有，每个qp只初始化一次

float *BitCost::s_bitsizes;//申请空间大小为 2*32768+1   MVD估计占用bits表格,例如：当前MV.x = 3 ,则其占用bits 为 s_bitsizes[3] 2*(log2(3+1))+e-1
/*
s_bitsizes[0] = e - 2   s_bitsizes[i]= 2*(log2(i+1))+e-1  log2 表示以2为底
s_bitsizes[1] = 2log2(2) + e -1
**/

Lock BitCost::s_costCalcLock;//多线程锁

/** 函数功能             ：建立MVD估计占用bits表格,例如：当前MV.x = 3 ,则其占用bits 为 s_bitsizes[3] 2*(log2(3+1))+e-1
* \返回                  ：null * */
void BitCost::CalculateLogs()
{
    if (!s_bitsizes)     //没有申请空间，在此申请,所有ME共有，所以一般只进入一次
    {
        s_bitsizes = new float[2 * BC_MAX_MV + 1];  //空间大小：32786*2+1
        s_bitsizes[0] = 0.718f;
        float log2_2 = 2.0f / log(2.0f);  // 2 x 1/log(2) double log (double); 以e为底的对数 e = 2.718281828459
        for (int i = 1; i <= 2 * BC_MAX_MV; i++)
            s_bitsizes[i] = log((float)(i + 1)) * log2_2 + 1.718f;
        /*
        s_bitsizes[0] = e - 2， s_bitsizes[i]= 2*(log2(i+1))+e-1， log2表示以2为底
        s_bitsizes[1] = 2log2(2) + e -1
        **/
    }
}
/** 函数功能   ： 释放空间内存
* \返回        ： null */
void BitCost::destroy()
{
    for (int i = 0; i < BC_MAX_QP; i++)
    {
        if (s_costs[i])
        {
            delete [] (s_costs[i] - 2 * BC_MAX_MV);

            s_costs[i] = 0;
        }
    }

    delete [] s_bitsizes;
    s_bitsizes = 0;
}