MMX 'less than' intrinsic mask

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How do I mask a less than in MMX intrinsics?
I only see "greater than" intrinsic in MMX intrinsic instructions.

C++

if (x <20)
  b =y+f;
else
  b =y;

Posted 13-Oct-10 1:50am

SMART LUBOBYA

Updated 13-Oct-10 2:16am

Sandeep Mewara

v2

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Sauro Viti · Answer 1 · 2010-10-13T02:22:00

Solution 3

If you have the "greater than" intrinsic, why don't you swap the operands?

C++

if (20 > x) // Same than x < 20 but using the greater than operator :-)
   b = y + f;
else
   b = y;

Posted 13-Oct-10 2:22am

Sauro Viti

Updated 13-Oct-10 2:49am

v4

Comments

CPallini 13-Oct-10 8:39am

Sure! My (now deleted) answer was probably driven by caffeine shortage!

LittleYellowBird 14-Oct-10 3:45am

Hi, this is not quite right as it does not take into account == 20, you either need to check for == or change 20 to 19. :)

Sauro Viti 14-Oct-10 4:41am

Sorry, but I don't agree with you: to test "x < 20" or "20 > x" is absolutely the same. What you are talking about is "x <= 20" which is the same than "21 > x"; or implementing "x < 20" as "!(x >= 20)".

LittleYellowBird · Answer 2 · 2010-10-13T02:22:00

Solution 2

Hi,

I am not very familiar with MMX intrinsics and there does not appear to be a 'less than', but surely if you check for 'greater than' and 'equal to' then the else is 'less than'?

Hope this helps :)

Posted 13-Oct-10 2:22am

LittleYellowBird

MMX 'less than' intrinsic mask

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