SSE 乘法 16 x uint8_t [英] SSE multiplication 16 x uint8_t

问题描述

我想用 SSE4 乘以具有 16 个无符号 8 位整数的 __m128i 对象，但我只能找到一个用于乘以 16 位整数的内在函数.有没有_mm_mult_epi8之类的东西?

I want to multiply with SSE4 a __m128i object with 16 unsigned 8 bit integers, but I could only find an intrinsic for multiplying 16 bit integers. Is there nothing such as _mm_mult_epi8?

推荐答案

MMX/SSE/AVX 中没有 8 位乘法.但是，您可以使用 16 位乘法来模拟 8 位乘法内在函数，如下所示:

There is no 8-bit multiplication in MMX/SSE/AVX. However, you can emulate 8-bit multiplication intrinsic using 16-bit multiplication as follows:

inline __m128i _mm_mullo_epi8(__m128i a, __m128i b)
{
    __m128i zero = _mm_setzero_si128();
    __m128i Alo = _mm_cvtepu8_epi16(a);
    __m128i Ahi = _mm_unpackhi_epi8(a, zero);
    __m128i Blo = _mm_cvtepu8_epi16(b);
    __m128i Bhi = _mm_unpackhi_epi8(b, zero);
    __m128i Clo = _mm_mullo_epi16(Alo, Blo);
    __m128i Chi = _mm_mullo_epi16(Ahi, Bhi);
    __m128i maskLo = _mm_set_epi8(0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 14, 12, 10, 8, 6, 4, 2, 0);
    __m128i maskHi = _mm_set_epi8(14, 12, 10, 8, 6, 4, 2, 0, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80);
    __m128i C = _mm_or_si128(_mm_shuffle_epi8(Clo, maskLo), _mm_shuffle_epi8(Chi, maskHi));

     return C;
}

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