Extract 4 SSE integers to 4 chars

Question

Suppose I have a __m128i containing 4 32-bit integer values.

Is there some way I can store it inside a char[4], where the lower char from each int value is stored in a char value?

Desired result:

           r1          r2          r3          r4
__m128i    0x00000012  0x00000034  0x00000056  0x00000078

  |
  V

char[4]    0x12        0x34        0x56        0x78

SSE2 and below is preferred. Compiling on MSVC++.

Marat Dukhan · Accepted Answer · 2013-10-06T20:50:40.190

4

With SSE2 you can use the following code:

char[4] array;
x = _mm_packs_epi32(x, x);
x = _mm_packus_epi16(x, x);
*((int*)array) = _mm_cvtsi128_si32(x);

edited Oct 06 '13 at 20:50

answered Oct 06 '13 at 20:10

Marat Dukhan

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Should that not say `*(int*)` instead of just `(int*)`? – us2012 Oct 06 '13 at 20:11

score 2 · Answer 2 · edited May 23 '17 at 12:16

2

Just for completeness, with SSSE3 you can do it with only one shuffling operation using _mm_shuffle_epi8. See here. You do consume one register more though, it depends on what is more important for you.

edited May 23 '17 at 12:16

Community

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answered Mar 20 '15 at 13:32

Antonio

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Unfortunately the OP wants this to work on SSE2, but yes, with SSSE3 it's much easier. – Paul R Mar 20 '15 at 14:02
@PaulR Yes, I should have pointed out that was SSSE3, and I had missed that line from OP. Thanks! – Antonio Mar 20 '15 at 14:11

Extract 4 SSE integers to 4 chars

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