SSE比较本质-如何从比较中获得1或0？ [英] SSE Comparison Intrinsics - How to get 1 or 0 from a comparison?

问题描述

我正在尝试使用SSE内在函数编写等价的if语句。

I am trying to write the equivalent of an if statement with SSE intrinsics.

我正在使用 __ m128 _mm_cmplt_ps（__ m128 a，__m128 b ）进行比较< b，如果比较分别为true或false，则返回 0xffffffff 或 0x0 。我想将这些值转换为1和0。为此，实现逻辑和 __ m128 _mm_and_ps（__ m128 c，__m128 d）是否正确？ ，其中 c 是转换的结果， d 是例如 0xffffffff ？

I am using __m128 _mm_cmplt_ps(__m128 a, __m128 b) to do the comparison a < b, and this returns 0xffffffff or 0x0 if the comparison was respectively true or false. I would like to convert these values into 1 and 0. In order to do this, is it correct to implement the logical "and" __m128 _mm_and_ps(__m128 c , __m128 d), where c is the result of the conversion and d is, e.g., 0xffffffff?

谢谢您的关注。

推荐答案

您正在比较要获得 1 或 0 ，然后乘以另一个数字。基本上就是这样：

You're comparing to get a 1 or a 0, then multiplying by another number. That is essentially this:

c = (a < b) * d;

与此相同：

c = 0;
if (a < b)
    c = d;

这也称为有条件移动。

如果这就是您想要的，那么您就不需要 0 或 1 。

If that's what you want, then you don't need the 0 or the 1. Just AND the result of the compare directly with the number you will multiply with.

__m128 c = _mm_cmplt_ps(a,b);
c = _mm_and_ps(c,d);

之所以有用，是因为比较结果全部返回了 0 或所有 1 。因此，将它们与结果进行与运算将使其为零，或完全保留该结果。

This works because the comparison returns either all 0's or all 1's. So ANDing them with the result will either zero it, or keep it entirely.

这是有意设计的。不需要乘法。

It was intentionally designed that way. There's no need for a multiplication.

这篇关于SSE比较本质-如何从比较中获得1或0？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！