Slow compares with int16's

[evsource]

I'm trying to speed up a section of code, and noticed that the following surprised me with the number of instructions it involves:

[vinniewryan]

That's just what it takes, as far as I know from how the condition works, it's comparing each bit from the highest of the int16 to the lowest, so it will compare each bit until it reaches the conclusion to the condition.

If firstvar is significantly greater than secondvar, it may be faster to use the following:

instead of:
if(first_variable > second_variable) //this should check each bit backwards until it reaches 'second_variable'

use:
if(second_variable < first_variable) //this should check each bit backwards until it reaches 'first variable'

Otherwise if you can use int8 instead of int16, it will also speed things up.
_________________
Vinnie Ryan

[Ttelmah]

It is basically 'what it takes'.
It doesn't do any form of bitwise comparison, it just performs a 16bit subtraction. However it is already quite efficient, in that lumps of the code are skipped if they "can't" apply.
Where you can save cycles, is in where the values are stored.
Nearly half the code, is basically switching banks to address the two values.
Two things apply. You will save a couple of instructions straight away, if the two values are in the same bank (declare them together). You can save more, by ensuring that they are in the bottom bank. Basically as a general 'layout' thing, declare the values which have the biggest effect on your code timing 'early' in your variable declarations. A search here, will find threads about the effect on speed of variable declaration order.

Best Wishes

[sjb]

Well, I get...

[Ttelmah]

As I said, memory placement.
The big difference here, is that your two variables are adjacent, right at the bottom of memory.
So, if I simply declare two variables at the start of the code, placing them nice and low in memory, I get: