Simple Sum - One negative, one positive

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BatVink

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Posted: 29th Mar 2016 21:12

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I am making a simple check to see if value a is negative while value b is positive, or vice versa. Is there any better way than this...

if (a < 0 and b > 0) or (a > 0 and b < 0)
// do something

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Paronamixxe

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Posted: 29th Mar 2016 21:28 Edited at: 29th Mar 2016 21:29

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I don't know if it's better, but maybe...

+ Code Snippet

If ( ( a / Abs ( a ) ) + ( b / Abs ( b ) ) ) = 0 Then // do something

Might be something? At the very least it only checks one equation.

cheers

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Matty H

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Posted: 29th Mar 2016 21:38

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if you multiply a negative number with a positive number then the answer will always be negative. Two positives or two negatives multiplied are always positive .

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BatVink

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Posted: 30th Mar 2016 08:31

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Thanks

I think Matty's solution is the most efficient, and it is one of those moments...why didn't I think of that?

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nickele upgraded

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Posted: 30th Mar 2016 09:08

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Sorry for interrupting , but if we use something like:
if ((a && b) >> 31) then **do something**
wouldn't it be a little bit faster (because of the bitwise operation)?
That's because if a,b are integers, then the expression logically ANDs the two values and takes the most significant bit (shifting 31 times to right).
If a,b have different signs, the result is always 1.

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nickele upgraded

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Posted: 30th Mar 2016 09:11

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Apologies for the inaccuracy.
I meant something like:
if ((a * b) >> 31)
Apologies again.

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baxslash

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Posted: 30th Mar 2016 11:47

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if a*b<0 should be fast enough most of the time... unless this is being used thousands of times per loop is it worth worrying about?

Using AppGameKit V2 Tier 1

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BatVink

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Posted: 30th Mar 2016 13:12

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Quote: "unless this is being used thousands of times per loop is it worth worrying about?"

valid point

I'm aiming at very low specced devices (think fruit-desert based devices

) and trying to keep to 60FPS as it is a reaction based app.
But I'm always keen to find efficient ways to do things.

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