14.2.1 MPEG-4编/解码设计与剖析（10）

void decoder_mbinter(DECODER * dec, const MACROBLOCK * pMB,
const uint32_t x_pos, const uint32_t y_pos, 
const uint32_t cbp, Bitstream * bs,
const uint32_t rounding, const int ref, const int bvop)
{
uint32_t stride = dec->edged_width;
uint32_t stride2 = stride / 2;
uint32_t i;
uint8_t *pY_Cur, *pU_Cur, *pV_Cur;
int uv_dx, uv_dy;
VECTOR mv[4]; /* local copy of mvs */
/*获取指向图像空间的指针*/
pY_Cur = dec->cur.y + (y_pos << 4) * stride + (x_pos << 4);
pU_Cur = dec->cur.u + (y_pos << 3) * stride2 + (x_pos << 3);
pV_Cur = dec->cur.v + (y_pos << 3) * stride2 + (x_pos << 3);
for (i = 0; i < 4; i++)   mv[i] = pMB->mvs[i]; /*获取运动向量*/
validate_vector(mv, x_pos, y_pos, dec);       /*检查运动向量的合法性*/
/******************************运动补偿*****************************/
if ((pMB->mode != MODE_INTER4V))
{ /* 编码模式是INTER、INTER_Q、NOT_CODED、FORWARD、BACKWARD */
uv_dx = mv[0].x;
uv_dy = mv[0].y;
uv_dx = (uv_dx >> 1) + roundtab_79[uv_dx & 0x3];
uv_dy = (uv_dy >> 1) + roundtab_79[uv_dy & 0x3];
/*亮度插值*/
interpolate16x16_switch(dec->cur.y,dec->refn[ref]
.y,16*x_pos,16*y_pos,mv[0].x, mv[0].y, stride, rounding);
} 
/*色度插值 */
interpolate8x8_switch(dec->cur.u, dec->refn[ref]
.u, 8 * x_pos, 8 * y_pos,uv_dx, uv_dy, stride2, rounding);
interpolate8x8_switch(dec->cur.v, dec->refn[ref].
v, 8 * x_pos, 8 * y_pos,uv_dx, uv_dy, stride2, rounding);
/******************************运动补偿*****************************/
/*根据cbp*/
if (cbp) decoder_mb_decode(dec, cbp, bs, pY_Cur, pU_Cur, pV_Cur, pMB);
}

void decoder_mb_decode(DECODER * dec, const uint32_t cbp, Bitstream * bs,
uint8_t * pY_Cur, uint8_t * pU_Cur, uint8_t * pV_Cur,
const int reduced_resolution,const MACROBLOCK * pMB)
{
DECLARE_ALIGNED_MATRIX(block, 1, 64, int16_t, CACHE_LINE); /*系数*/
DECLARE_ALIGNED_MATRIX(data, 6, 64, int16_t, CACHE_LINE);  /*图像*/
int stride = dec->edged_width;   /*图像边扩展后的宽度*/
int next_block = stride * 8;    /*亮度的下一个块*/
const int stride2 = stride/2;    /*色度的下一个快*/
int i;
const uint32_t iQuant = pMB->quant;  /*量化步长*/
const int direction = dec->alternate_vertical_scan   2 : 0;  /*AC扫描方式*/
for (i = 0; i < 6; i++) {
if (cbp & (1 << (5 - i))) {       /*块做了编码*/
memset(block, 0, 64 * sizeof(int16_t));   /*清零*/
get_inter_block(bs, block, direction);   /*VLD熵解码*/
dequant_h263_inter (&data[i * 64], block, iQuant, NULL);/*H263反量化*/
idct(&data[i * 64]);        /*IDCT变换*/
}
}
/*根据CBP值决定是否加到当前图像*/
if (cbp & 32) transfer_16to8add(pY_Cur, &data[0 * 64], stride);
if (cbp & 16) transfer_16to8add(pY_Cur + 8, &data[1 * 64], stride);
if (cbp & 8)  transfer_16to8add(pY_Cur + next_block, &data[2 * 64], stride);
if (cbp & 4)  transfer_16to8add(pY_Cur + 8 + next_block, &data[3 * 64], stride);
if (cbp & 2)  transfer_16to8add(pU_Cur, &data[4 * 64], stride2);
if (cbp & 1)  transfer_16to8add(pV_Cur, &data[5 * 64], stride2);
}