Dear Forum,
I have experienced some strange behaviour using float/double values in a formula calculation.
Using the same static double values the result may differ each time I run the calculation?
I'm using a LPC824 (Cortex M0) with no FPU and KEIL-MDK. No MicroLIB and default compiler version 5
I'm aware of the usage of double/float precision issue. But this problem is when using the same values, the result is different each time I run a calculation.
I have a voltage (double) from a ADC, that is run through a formula, that uses 7 coefs (double).
The formula is this:
dResult = V0[paramIndex] + ( (dTemp-T0[paramIndex])*(P1[paramIndex]+(dTemp-T0[paramIndex])*(P2[paramIndex]+(dTemp-T0[paramIndex])*(P3[paramIndex]+P4[paramIndex]*(dTemp-T0[paramIndex]))))/( 1+(dTemp-T0[paramIndex])*(q1[paramIndex]+q2[paramIndex]*(dTemp-T0[paramIndex]))));
V0[], T0[], P1[], P2[], P3[], P4[], q1[] and q2[] contains static double values. So they do neve change.
dTemp is the double value (voltage) passed to the function containing the formula.
If I also keep the dTemp stable (fixed static value of 27.8125) the dResult is different each time I run the formula. If I use the value of 27.7812 it is the same value each time.
Why do I see this behavior? Why is the result not the same each time?
Thomas
The result posted by LPC User using the LPC845 gives the correct value?
Are you asking if my result is correct? I don't know. As I said before, I didn't try to understand the calculation.
The value shown is the dCalculation. I didn't report the intermediate values.
Yes, you result are the correct ones. My is a bit of.
But it seems to be related to setting the LPC824 into low power mode.