（十二）子宏块预测句法
sub_mb_pred( mb_type ) {
for( mbPartIdx = 0; mbPartIdx < 4; mbPartIdx++ )
// sub_mb_type[ mbPartIdx ] 指明子宏块的预测类型，在不同的宏块类型中这个句法元素的语义不一样。
sub_mb_type[ mbPartIdx ]
for( mbPartIdx = 0; mbPartIdx < 4; mbPartIdx++ )
if( ( num_ref_idx_l0_active_minus1 > 0 | |
mb_field_decoding_flag ) &&
mb_type != P_8x8ref0 &&
sub_mb_type[ mbPartIdx ] != B_Direct_8x8 &&
SubMbPredMode( sub_mb_type[ mbPartIdx ] ) != Pred_L1 )
ref_idx_l0[ mbPartIdx ]
for( mbPartIdx = 0; mbPartIdx < 4; mbPartIdx++ )
if( (num_ref_idx_l1_active_minus1 > 0 | | mb_field_decoding_flag )
&&
sub_mb_type[ mbPartIdx ] != B_Direct_8x8 &&
SubMbPredMode( sub_mb_type[ mbPartIdx ] ) != Pred_L0 )
ref_idx_l1[ mbPartIdx ]
for( mbPartIdx = 0; mbPartIdx < 4; mbPartIdx++ )
if( sub_mb_type[ mbPartIdx ] != B_Direct_8x8 &&
SubMbPredMode( sub_mb_type[ mbPartIdx ] ) != Pred_L1 )
for( subMbPartIdx = 0;
subMbPartIdx < NumSubMbPart( sub_mb_type[ mbPartIdx ] );
subMbPartIdx++)
for( compIdx = 0; compIdx < 2; compIdx++ )
mvd_l0[ mbPartIdx ][ subMbPartIdx ][ compIdx ]
for( mbPartIdx = 0; mbPartIdx < 4; mbPartIdx++ )
if( sub_mb_type[ mbPartIdx ] != B_Direct_8x8 &&
SubMbPredMode( sub_mb_type[ mbPartIdx ] ) != Pred_L0 )
for( subMbPartIdx = 0;
subMbPartIdx < NumSubMbPart( sub_mb_type[ mbPartIdx ] );
subMbPartIdx++)
for( compIdx = 0; compIdx < 2; compIdx++ )
mvd_l1[ mbPartIdx ][ subMbPartIdx ][ compIdx ]
}
（十三）残差句法
residual( ) {
if( !entropy_coding_mode_flag )
residual_block = residual_block_cavlc
else
residual_block = residual_block_cabac
if( MbPartPredMode( mb_type, 0 ) = = Intra_16x16 )
residual_block( Intra16x16DCLevel, 16 )
for( i8x8 = 0; i8x8 < 4; i8x8++ ) /* each luma 8x8 block */
for( i4x4 = 0; i4x4 < 4; i4x4++ ) /* each 4x4 sub-block of block */
if( CodedBlockPatternLuma & ( 1 << i8x8 ) ) {
if( MbPartPredMode( mb_type, 0 ) = = Intra_16x16 )
residual_block( Intra16x16ACLevel[ i8x8 * 4 + i4x4 ], 15 )
else
residual_block( LumaLevel[ i8x8 * 4 + i4x4 ], 16 )
} else {
if( MbPartPredMode( mb_type, 0 ) = = Intra_16x16 )
for( i = 0; i < 15; i++ )
Intra16x16ACLevel[ i8x8 * 4 + i4x4 ][ i ] = 0
else
for( i = 0; i < 16; i++ )
LumaLevel[ i8x8 * 4 + i4x4 ][ i ] = 0
}
for( iCbCr = 0; iCbCr < 2; iCbCr++ )
if( CodedBlockPatternChroma & 3 ) /* chroma DC residual present */
residual_block( ChromaDCLevel[ iCbCr ], 4 )
else
for( i = 0; i < 4; i++ )
ChromaDCLevel[ iCbCr ][ i ] = 0
for( iCbCr = 0; iCbCr < 2; iCbCr++ )
for( i4x4 = 0; i4x4 < 4; i4x4++ )
if( CodedBlockPatternChroma & 2 )
/* chroma AC residual present */
residual_block( ChromaACLevel[ iCbCr ][ i4x4 ], 15 )
else
for( i = 0; i < 15; i++ )
ChromaACLevel[ iCbCr ][ i4x4 ][ i ] = 0
}
（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 ]
}
}
}