逻辑运算符要明智吗？

Question

I'm working on a puzzle right now....trying to write if (x==5 || x==7) With bitwise operations (in C). Been working on it for a while....can't figure it out.

Any help would be appreciated! Thanks

Ps this isn't homework...trying to study for a test.

EDIT so the format would be something like if (x _ _) with a bitwise operation in the blanks

SORRY need to specify, can only be two characters (operator or numeric value) So %8 for example

Answer 1

7d = 111b and 5d = 101b

So bit 0 must be on, bit 1 is don't care, bit 2 must be on and bits 3-31 must be off. So, mask out bit 1 and test for 101b

so your test becomes ((x & ~2) == 5)

Then ask Bing or wikipedia about "Karnaugh Maps" so you can do your own expression reduction.

Tom's answer below is also correct and is simpler. You could write

((x & 5) == 5)

and this is slightly faster. Perhaps I should have used a Karnaugh map!

Answer 2

您可以将其与“ 101”进行“与”运算，则5和7的结果相同，即101。