ypedef struct Block16x16
{
    BYTE data[16][16];
} Block16x16;

typedef struct MV
{
    BYTE x;
    BYTE y;
} MV;

//Compute_SAD
// computes sad value between two blocks
//Input   16x16 block1
//Output  16x16 block2
//return  int sadValue
int Compute_SAD(BYTE block1[16][16], BYTE block2[16][16])
{
    int sadValue = 0;
    for (int i = 0; i < 16; i++)
    {
        for (int j = 0; j < 16; j++)
        {
            BYTE value1 = block1[i][j];
            BYTE value2 = block2[i][j];
            sadValue += abs(value1 - value2);
        }
    }
    return sadValue;
}

//startI, startJ are assumed to be multiples of 16
Block16x16 get16x16Block(BYTE *frame, int frameWidth, int startI, int startJ)
{
    Block16x16 block;
    for (int j = 0; j < 16; j++)
    {
        for (int i = 0; i < 16; i++)
        {
            block.data[i][j] = *(frame + (startI + i) + (startJ + j) * frameWidth);
        }
    }
    return block;
}

// Compute_MV
// computes motionVectors
// Input   16*16 block
// frame  redframe[YFrame,UFrame,VFrame]
// output returns motion vectors like {0,1}
MV Compute_MV(Block16x16 block, BYTE *frame)
{
    int offset = 0;
    int maxWidth = Y_frame_width;
    int maxHeight = Y_frame_height;
    int minValue = 65535;
    BYTE minI = 0, minJ = 0;

    for (int macroblock_Ypos = 0; macroblock_Ypos < maxHeight; macroblock_Ypos += 16)
    {
        for (int macroblock_Xpos = 0; macroblock_Xpos < maxWidth; macroblock_Xpos += 16)
        {
            Block16x16 frameBlock = get16x16Block(frame, maxWidth, macroblock_Xpos, macroblock_Ypos);
            int sad = Compute_SAD(block.data, frameBlock.data);
            if (sad < minValue)
            {
                minI = macroblock_Xpos;
                minJ = macroblock_Ypos;
                minValue = sad;
            }
        }
    }

    MV mv = {(MyDataSize)(minI/16), (MyDataSize)(minJ/16)};
    return mv;
}