RS41ng/src/locator.c

// Based on HamLib's locator routines
// OK1TE 2018-10

#include "locator.h"

const static uint8_t loc_char_range[] = {18, 10, 24, 10, 24, 10};
const float precision = 1E+7f;

void locator_from_lonlat(int32_t longitude, int32_t latitude, uint8_t pair_count, char *locator)
{
    for (uint8_t x_or_y = 0; x_or_y < 2; ++x_or_y) {
        float ordinate = ((x_or_y == 0) ? (longitude / 2.0f) / precision : latitude / precision) + 90;
        uint32_t divisions = 1;

        for (uint8_t pair = 0; pair < pair_count; pair++) {
            divisions *= loc_char_range[pair];
            const float square_size = 180.0f / divisions;

            uint8_t locvalue = (uint8_t) (ordinate / square_size);
            ordinate -= square_size * (float) locvalue;
            locvalue += (loc_char_range[pair] == 10) ? '0' : 'A';
            locator[pair * 2 + x_or_y] = locvalue;
        }
    }

    locator[pair_count * 2] = 0;
}