将 __m128i 中的每个 DW 右移不同的量 [英] Shift right every DW in a __m128i by a different amount

问题描述

我想将 __m128i 寄存器的每个元素右移不同的量.我知道如果我们想像下面这样左移，我知道这是可能的:

I want to shift right every element of a __m128i register by a different amount.I know this is possible by multiplication if we want to shift left like below:

__m128i mul_constant = _mm_set_epi32(8, 4, 2, 1);
__m128i left_vshift = _mm_mullo_epi32(R, mul_constant);

但是，如果我们想把它右移，有什么解决办法?

But, what is the solution if we want to shift it right?

推荐答案

我终于做到了如下:将每个字节向左移动不同的量，然后将 32 位右移 3 位得到了我想要的结果.

I finally did it like below: Shifting every byte by a different amount to left and then a 32-bit right shift by 3 gave me what I wanted.

 R = _mm_mullo_epi32(R, _mm_set_epi32(1, 2, 4, 8));
 R = _mm_srli_epi32(R, 3);

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