[英]Find min/max value from a __m128i
I want to find the minimum/maximum value into an array of byte using SIMD operations. 我想使用SIMD操作在字节数组中找到最小/最大值。 So far I was able to go through the array and store the minimum/maximum value into a __m128i variable, but it means that the value I am looking for is mixed among others (15 others to be exact). 到目前为止,我能够通过数组并将最小/最大值存储到__m128i变量中,但这意味着我正在寻找的值与其他值混合在一起(确切地说是15个其他值)。
I've found these discussions here and here for integer, and this page for float, but I don't understand how works _mm_shuffle*. 我在这里和这里找到了这些讨论的整数, 这个页面用于浮点数,但我不明白如何工作_mm_shuffle *。 So my questions are: 所以我的问题是:
Here is an example for horizontal max for uint8_t
: 以下是uint8_t
水平最大值示例:
#include "tmmintrin.h" // requires SSSE3
__m128i _mm_hmax_epu8(const __m128i v)
{
__m128i vmax = v;
vmax = _mm_max_epu8(vmax, _mm_alignr_epi8(vmax, vmax, 1));
vmax = _mm_max_epu8(vmax, _mm_alignr_epi8(vmax, vmax, 2));
vmax = _mm_max_epu8(vmax, _mm_alignr_epi8(vmax, vmax, 4));
vmax = _mm_max_epu8(vmax, _mm_alignr_epi8(vmax, vmax, 8));
return vmax;
}
The max value will be returned in all elements. 最大值将在所有元素中返回。 If you need the value as a scalar then use _mm_extract_epi8
. 如果您需要将值作为标量,请使用_mm_extract_epi8
。
It should be fairly obvious how to adapt this for min, and for signed min/max. 应该相当明显如何适应min,以及签名的min / max。
Alternatively, convert to words and use phminposuw
(not tested) 或者,转换为单词并使用phminposuw
(未测试)
int hminu8(__m128i x)
{
__m128i l = _mm_unpacklo_epi8(x, _mm_setzero_si128());
__m128i h = _mm_unpackhi_epi8(x, _mm_setzero_si128());
l = _mm_minpos_epu16(l);
h = _mm_minpos_epu16(h);
return _mm_extract_epi16(_mm_min_epu16(l, h), 0);
}
By my quick count, the latency is a bit worse than a min/shuffle cascade, but the throughput a bit better. 根据我的快速计算,延迟比min / shuffle级联稍差,但吞吐量稍微好一些。 The linked answer with phminposuw
is probably better though. 与phminposuw
相关的答案可能更好。 Adapted for unsigned bytes (but not tested) 适用于无符号字节(但未经过测试)
uint8_t hminu8(__m128i x)
{
x = _mm_min_epu8(x, _mm_srli_epi16(x, 8));
x = _mm_minpos_epu16(x);
return _mm_cvtsi128_si32(x);
}
You could use it for max too, but with a bit of overhead: complement the input and result. 您也可以将它用于最大值,但有一点开销:补充输入和结果。
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