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CCS math functions bug?

 
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autobots
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CCS math functions bug?
PostPosted: Tue Dec 29, 2009 9:02 pm     Reply with quote
I'm using the maths function in my programs, but I found out there is a bug in some math functions.
So I purposely check it by just simply print out like this:
Code:
printf("%.4f\r\n",cos(0.7854));

the result I get is 0.7071, but result from my calculator is 0.9999.
as well as tan(0.7854) = 1 (in CCS).

Can I know what is the problem there?
I am using compiler version V4.088.
PCM programmer



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PostPosted: Tue Dec 29, 2009 9:19 pm     Reply with quote
The CCS manual says this:
Quote:

Syntax:
val = cos (rad)

Parameters:
rad is a float representing an angle in Radians -2pi to 2pi.
Value is a float.
mbradley



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PostPosted: Tue Dec 29, 2009 9:20 pm     Reply with quote
This is correct, cos(0.7854) = .7071

You might be using Degrees on your calculator, not Radians. Switch your calculator over to Radians, and try again.

Try this: cos(0.7854/57.2957795)

simple macro:

#define deg2rad(d) (d / 57.2957795)
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Michael Bradley
www.mculabs.com
Open Drivers and Projects
a
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PostPosted: Tue Dec 29, 2009 9:51 pm     Reply with quote
ok..sorry my mistaken..
thanks for the reply.
Smile
Ttelmah
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PostPosted: Wed Dec 30, 2009 6:11 am     Reply with quote
As a 'comment', make the macro:
Code:


#define deg2rad(d) (d * 0.01745329)


This is a general rule', that multiplication, is always faster than division (applies even on the fast maths hardware on a PC, by a couple of clock cycles), but on the PIC, the difference really 'matters'. On a PIC16, using a multiplication, rather than a division, halves the time. In a PIC18 (wth the hardware multiplier), it improves things by a factor of nearly 4*.....
So it is worth getting into the habit, when dealing with constants like this, of always generating the 'reciprocal' value, and multiplying, rather than using division. Smile

Best Wishes (and Happy New Year).
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