H.264句法和语法总结（十四）CAVLC 残差句法

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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 ]             
        }           
    }           
}

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