What does this x86 SSE code do?

Question

I see this piece of code in OpenCV.

__m128i delta = _mm_set1_epi8(-128),
        t = _mm_set1_epi8((char)threshold),
        K16 = _mm_set1_epi8((char)K);
(void)K16;
(void)delta;
(void)t;

Can someone explain to me what it does ? All I got is what the sse functions do but what happens in next three line is unclear

You mean, "Why are all the variables being used as `(void)v`?" — user2864740, Jun 10 '14 at 00:11
possible duplicate of [Why cast an unused value to void?](http://stackoverflow.com/questions/4647665/why-cast-an-unused-value-to-void) — Paul R, Jun 10 '14 at 05:56
It's possible they're used as some sort of optimization barriers? — Drew McGowen, Jun 10 '14 at 15:54
Git history comment for the changeset that introduce those says "warnings under windows". So, the intention would have been to quiet unused value warning. — SleuthEye, Jun 11 '14 at 02:16

score 0 · Answer 1 · answered Jun 10 '14 at 00:12

0

Sets the 128 bit value to the signed char input in 8-bit strides: http://msdn.microsoft.com/en-us/library/6e14xhyf(v=vs.90).aspx

answered Jun 10 '14 at 00:12

user3712302

26
1

2

Oh, sorry I misread your question. The void casts might be there to stop the compiler from complaining about those vars being unused. Are they used further on in the code? – user3712302 Jun 10 '14 at 00:14
2

Yes they are used. (Refer to fast.cpp if you have opencv code) – adikshit Jun 10 '14 at 00:21

What does this x86 SSE code do?

1 Answers1