H.264句法和语法总结（十四）CAVLC 残差句法

residual_block_cavlc( coeffLevel, maxNumCoeff ) {  C      Descriptor

    for( i = 0; i < maxNumCoeff; i++ )          

        coeffLevel[ i ] = 0     

    // coeff_token      指明了非零系数的个数，拖尾系数的个数。      

    coeff_token 

    if( TotalCoeff( coeff_token ) > 0 ) {          

        if( TotalCoeff( coeff_token ) > 10    &&    TrailingOnes( coeff_token ) <

3 )

            suffixLength = 1          

        else          

            suffixLength = 0          

        for( i = 0; i < TotalCoeff( coeff_token ); i++ )          

            if( i < TrailingOnes( coeff_token ) ) {           

                // trailing_ones_sign_flag  拖尾系数的符号

                    -     如果trailing_ones_sign_flag = 0,  相应的拖尾系数是+1。

                    -     否则，trailing_ones_sign_flag =1，相应的拖尾系数是-1。 

                trailing_ones_sign_flag  

                level[ i ] = 1 – 2 * trailing_ones_sign_flag          

            } else {          

                // level_prefix and level_suffix  非零系数值的前缀和后缀。 

                level_prefix 

                levelCode = ( level_prefix << suffixLength )          

                if( suffixLength > 0    | |    level_prefix >= 14 ) {          

                    level_suffix  

                    levelCode += level_suffix          

                }          

                if( level_prefix    = =    15    &&    suffixLength    = =    0 )          

                    levelCode += 15          

                if( i    = =    TrailingOnes( coeff_token )    &&    

                      TrailingOnes( coeff_token ) < 3 )

                    levelCode += 2          

                if( levelCode % 2    = =    0 )          

                    level[ i ] = ( levelCode + 2 ) >> 1          

                else          

                    level[ i ] = ( –levelCode – 1 ) >> 1          

                if( suffixLength    = =    0 )          

                    suffixLength = 1          

                if( Abs( level[ i ] )    >    ( 3 << ( suffixLength – 1 ) )    &&    

                      suffixLength < 6 )

                    suffixLength++          

            }          

        if( TotalCoeff( coeff_token ) < maxNumCoeff ) {          

            // total_zeros    系数中 0 的总个数。

            total_zeros   

            zerosLeft = total_zeros          

        } else          

            zerosLeft = 0          

        for( i = 0; i < TotalCoeff( coeff_token ) – 1; i++ ) {          

            if( zerosLeft > 0 ) {          

                run_before   

                run[ i ] = run_before          

            } else          

                run[ i ] = 0          

            zerosLeft = zerosLeft – run[ i ]          

        }          

        run[ TotalCoeff( coeff_token ) – 1 ] = zerosLeft          

        coeffNum = -1          

        for( i = TotalCoeff( coeff_token ) – 1; i >= 0; i-- ) {          

            coeffNum += run[ i ] + 1          

            coeffLevel[ coeffNum ] = level[ i ]            

        }          

    }          

}