Extract non-zero byte from _m128i

[Ravi_K_]

Hi, I have 4 _m128i 64byte elements which can contain 0 or non-zero (+ve, -ve) values. I want to extract non-zero values from them. I looked at _mm_extract_epi8/_mmextract_epi16 but the syntax is int _mm_extract_epi16 (__m128i a, int imm) where imm is the index, hence I have to loop to get non-zero values. Any intrinsics functions that can be used to avoid loop will be helpful. Inputs appreciated. Thanks.

[andysem]

I'm thinking _mm_cmpeq_epi8, _mm_movemask_epi8 and then dispatch through a table of pointers to series of _mm_extract_epi8. But I'm not sure this approach will be beneficial compared to a regular std::find_if in memory.

[jimdempseyatthecove]

Ravi,

Can you describe in more detail (widen the scope of your description) of what you are trying to do?

IOW are you intending to squish out the 0's of 4 x _mm_epi8 registers (to left, to right, across registers), or is this a squish of a larger number of bytes in memory?

Jim Dempsey

[Ravi_K_]

Thanks andysem for your inputs, will look into it. Jim, I want to use it for ipv6 source/destination address and mask and want to implement TCAM like Longest-Prefix-Match behavior. Thanks.