optimize and if statement

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Victor
Victor 2014-1-24
评论： Victor 2014-1-24
I am running code that runs through a loop millions of times. I am trying to make the loop as effect as possible. The loop cannot be arrayed as future values depend on previous values. I used the profiler to see what was taking the most time in the loop. The line that is taking the the most time is an if statement:
if abs((a-b)/b) <.000001
Is there any way to speed this line up? change in the structure of the if or change in the way the condition is evaluated?

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回答（2 个）

Walter Roberson
Walter Roberson 2014-1-24
if b * 0.999999 < a & a < b * 1.000001
better recheck as it is pretty late at night for me.
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Victor
Victor 2014-1-24
Thanks for the reply. I tried your suggestion and it appears to take longer.

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David Sanchez
David Sanchez 2014-1-24
You can try with different combinations like:
if abs((a-b)/b)*10^6 <1
if -1<(a-b)*10^6/b && (a-b)*10^6/b <1
if -.000001<(a-b)/b && (a-b)/b <.000001
if abs((a-b)/b) <1/1000000
if -b<(a-b)*10^6 && (a-b)*10^6 <b
but the time taken to check the condition is very similar in all of them. I think you can't hardly improve much the speed of that line.

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