Code Composer and MSP430FR5969 - problem with the calculations

Wojciech Dudek

Other Parts Discussed in Thread: MSP430FR5969

Hi,

Can someone explain my whats going on with the Code Composer Studio?

Im did this code to show the problem. Calculations are wrong, and I don't know whats going on. This works on MSP430FR5969 launchpad.

#include <msp430.h>

long double a,b,c;
int test;

int main(void) {
	WDTCTL = WDTPW | WDTHOLD;

	a = 32768 / 572;
	b = a / 2;
	c = b * 60;

	test = ((32768/572)/2)*60;

	while(1);
}

I guess that CC is configurated wrong, what should I do to see right calculations?

over 8 years ago

0 zrno soli over 8 years ago

Guru 34483 points

First result (related to a, b, c) is done by floating point numbers / operators. Second result (related to test) is done by integer numbers / operators. Because of this there is difference between 1.71e+03 and 1680.

0 Wojciech Dudek over 8 years ago in reply to zrno soli

Prodigy 90 points

I know that, but it looks like results are somehow rounded. Variable test should be 1718.6013986 with double and 1718 in integer, not 1710 and 1680. What should I do to get results I want?

0 Chester Gillon over 8 years ago

Guru 92251 points

Wojciech Dudek said:
a = 32768 / 572;

Since the constants in that expression are implicitly integer the compiler has performed an integer division and stored the result of the integer division (57) in a.

Try making the constants explicitly double:

	a = 32768.0 / 572.0;

0 Wojciech Dudek over 8 years ago in reply to Chester Gillon

Prodigy 90 points

Now it's fine, thank you very much. :)

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Code Composer and MSP430FR5969 - problem with the calculations