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evsource
Joined: 21 Nov 2006
Posts: 129
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| float to int question |
 Posted: Tue Sep 01, 2009 6:23 pm |
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Hi,
I know I can cast a float to an int, e.g:
| Code: |
int the_int;
float the_float;
the_float = 8.5;
the_int = (int) the_float;
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... and the result will be "8".
However, if I have a float variable that is percentages, and want to do a fast conversion on a 18F chip to an int, how can I do that?
If I cast the float to an int, anything below 100% will be 0. Sure, I can multiply by 100, then cast to an int, but on a 18F chip at 40mHz, that's going to cost me about 35us ... too long.
Any suggestions? |
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vinniewryan
Joined: 29 Jul 2009
Posts: 154
Location: at work
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| Posted: Tue Sep 01, 2009 6:40 pm |
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You could do | Code: | | the_int=(100 - the_float) |
which would return a value you can work with, if indeed 100% is the greatest value the_float will hold. |
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evsource
Joined: 21 Nov 2006
Posts: 129
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| Posted: Tue Sep 01, 2009 9:39 pm |
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| vinniewryan wrote: | You could do | Code: | | the_int=(100 - the_float) |
which would return a value you can work with, if indeed 100% is the greatest value the_float will hold. |
Hmm... I'm not sure that's what I'm after.
e.g.
| Code: |
the_float = 0.08; // 8%
the_int = (int)(100 - the_float); |
the_int will be "99" if I understand things correctly. The desired result is "8".
Just some background, the value that is a float needs to be transmitted over a serial communications line. I know I could do fixed-point arithmetic to avoid using the float altogether, but it seems like the right thing to do in code, using the float. But to transmit it, I only want to send one byte, since all I want in the transmitted data is 0-100%, in integer increments.
I was just curious if there was a way to get the float into an integer in less than 35us on a 40mHz 18F chip. |
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vinniewryan_guest
Guest
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| Posted: Wed Sep 02, 2009 12:03 am |
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Oh I see, I didn't realize you would be working with numbers less than 1. Now that I think about it, it was just an overall thoughtless answer.
I can't think of any other methods of rounding a percent to a whole number without multiplying. Sorry. |
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