使用SSE的水平最小和最大 [英] Horizontal minimum and maximum using SSE

问题描述

我有一个使用SSE进行很多工作的函数，分析器向我显示，我用来计算水平最小和最大水平的代码部分大部分时间都在消耗.

I have a function using SSE to do a lot of stuff, and the profiler shows me that the code portion I use to compute the horizontal minimum and maximum consumes most of the time.

例如，我一直在使用以下实现作为最低要求:

I have been using the following implementation for the minimum for instance:

static inline int16_t hMin(__m128i buffer) {
    buffer = _mm_min_epi8(buffer, _mm_shuffle_epi8(buffer, m1));
    buffer = _mm_min_epi8(buffer, _mm_shuffle_epi8(buffer, m2));
    buffer = _mm_min_epi8(buffer, _mm_shuffle_epi8(buffer, m3));
    buffer = _mm_min_epi8(buffer, _mm_shuffle_epi8(buffer, m4));
    return ((int8_t*) ((void *) &buffer))[0];
}

如您所见，我需要计算16个1字节整数的最小值和最大值.

I need to compute the minimum and the maximum of 16 1-byte integers, as you see.

任何好的建议都会受到高度赞赏:)

Any good suggestions are highly appreciated :)

谢谢

推荐答案

我建议进行两项更改:

• 用_mm_cvtsi128_si32替换((int8_t*) ((void *) &buffer))[0].

• 用_mm_shuffle_epi32/_mm_shufflelo_epi16替换_mm_shuffle_epi8，它们在最新的AMD处理器和Intel Atom上具有较低的延迟，并且可以节省内存加载操作:

• Replace ((int8_t*) ((void *) &buffer))[0] with _mm_cvtsi128_si32.

• Replace _mm_shuffle_epi8 with _mm_shuffle_epi32/_mm_shufflelo_epi16 which have lower latency on recent AMD processors and Intel Atom, and will save you memory load operations:

static inline int16_t hMin(__m128i buffer)
{
    buffer = _mm_min_epi8(buffer, _mm_shuffle_epi32(buffer, _MM_SHUFFLE(3, 2, 3, 2)));
    buffer = _mm_min_epi8(buffer, _mm_shuffle_epi32(buffer, _MM_SHUFFLE(1, 1, 1, 1)));
    buffer = _mm_min_epi8(buffer, _mm_shufflelo_epi16(buffer, _MM_SHUFFLE(1, 1, 1, 1)));
    buffer = _mm_min_epi8(buffer, _mm_srli_epi16(buffer, 8));
    return (int8_t)_mm_cvtsi128_si32(buffer);
}

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