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Calculating Sin/Cos with GFLIB

Question asked by Andy Berger on Mar 21, 2018
Latest reply on Mar 22, 2018 by Andy Berger

I am trying to write some simple code making use of GFLIB for an ARM Cortex M4F MCU. I have successfully included the library files, and have some code making use of the GFLIB_Sin_FLT_C function from gflib_FP.h:


In the below code, I am trying to build a sine-wave array (and phase-shifted copies) and store them in current_U, current_V, and current_W.


int main(void) {
float current_U[36];
float current_V[36];
float current_W[36];
int i;

for(i=0; i<NUM_PTS; i++) {
current_U[i] = GFLIB_Sin_FLT_C(i*10*PI/180.0); // input argument in radians
current_V[i] = GFLIB_Sin_FLT_C(i*10*PI/180.0 + 2*PI/3); // phase shift by +120deg
current_W[i] = GFLIB_Sin_FLT_C(i*10*PI/180.0 - 2*PI/3); // phase shift by -120deg  



Strangely, the current_V calculation gives erroneous results:


Why would this be? Since GFLIB is a pre-compiled library, I can't examine the code that is calculating the sine value. Why would the calculation only fail for one of the function calls?