使用__m64数据类型实现if-else [英] Implementing if-else with __m64 data types

问题描述

我如何使用if- else并在下面的代码段中处理第2步中的Adjust ??

how do i use if- else and treat Adjust in step 2 for the snippet codes below?

.h file
 class tom
{
.
.
.
protected:
    static const int Adjust[6];

protected:
    int _mode;

    int _q;
    int _qm;
    int _qe;
    int _f;
    int _scale
};

.cpp file
const int tom::Adjust[6] =
{
    107,
    916,
    182,
    362,
    192,
    282
};

tom::tom()
{

    _q          = 1;
     _qm        =_q % 6;
    _qe         = _q/6;
    _f          = (1 << (15+_qe))/6;
    _scale  = 15+_qe;
}

void tom::calculate(void* ptr)
{
    short* block = (short *)ptr;
    int j;

     __m64*block1 = (__m64*)block;
     __m64 s0,s1,s2,s3,x0,x1,x2,x3;
      j=0;
        //step 1
s0 =_mm_add_pi16(block1[j],block1[j+3]);
s3 =_mm_sub_pi16(block1[j],block1[j+3]);
s1 =_mm_add_pi16(block1[j+1],block1[j+2]);
s2 =_mm_sub_pi16(block1[j+1],block1[j+2]);

      // step 2
 x0 =_mm_add_pi16(s0,s1);
 if(x0 < 0)
block[j] = (short)(-( (((-x0) * Adjust[_qm]) + _f) >> _scale ));
else
block[j] = (short)( ((x0 * Adjust[_qm]) + _f) >> _scale );
.
.
.
.

_mm_empty();

}

推荐答案

对我来说，您的目标不是很清楚，因为x0是用于存储4个整数(每个16位)，我想代码段中的if-else表示类似:如何对这4个数字中的每个进行这种条件计算" .
如果这是您的要求，可以使用以下公式解决问题:

short s = 1 - (n >> 15) * 2

其中n是short;如果n >= 0，s的值为1，如果n < 0

It''s not so clear for me what is your target, however, as x0 is an _m64 variable used to store 4 integers (16 bit each one), I suppose that with the if-else in your snippet, you mean something like: "how to do this kind of conditional calculation for each of the 4 numbers".
If this is your requirement, pheraps you can work around this formula:

short s = 1 - (n >> 15) * 2

Where n is a short; the value of s will be 1 if n >= 0 and -1 if n < 0

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