sht3x-test.c

#include <math.h>
#include <stdio.h>
#include <stdlib.h>

// esp8266 code size using double's: 223 bytes
// esp8266 code size using floats: 204 bytes
float datasheet_calc(int stemp) {
        float temp = (stemp * 175.0f) / 65535.0f - 45.0f;
        return temp;
}

// esp8266 code size 199 bytes
float simplified_calc(int stemp) {
        stemp = ((4375 * stemp) >> 14) - 4500;
        float temp = (float)stemp / 100.0f;
        return temp;
}

// esp8266 code size 199 bytes
float improved_int_calc(int stemp) {
        const int i_scale = 128;
        stemp = (((i_scale/4 * 175) * stemp) >> 14) - (i_scale * 45);
        float temp = (float)stemp / (float) i_scale;
        return temp;
}

int main()
{
        float maxdiff_simplified = 0.0f;
        float maxdiff_improved = 0.0f;

        for (int i = (-40 + 45) * 375; i < /*65536*/ (90+45) * 375; ++i) {
                float ds_temp = datasheet_calc(i);
                float im_temp = improved_int_calc(i);
                float sc_temp = simplified_calc(i);

                //printf("%d: comparing %f with %f = %f\n",
                //      i, ds_temp, sc_temp, fabsf(ds_temp - sc_temp));

                if (fabs(ds_temp - sc_temp) > maxdiff_simplified) {
                        maxdiff_simplified = fabsf(ds_temp - sc_temp);
                }

                if (fabs(ds_temp - im_temp) > maxdiff_improved) {
                        maxdiff_improved = fabsf(ds_temp - im_temp);
                }

        }

        printf("maxdiff_simplified = %f maxdiff_improved = %f\n", maxdiff_simplified, maxdiff_improved);

        return 0;
}