int H3_EXPORT()

in src/h3lib/lib/algos.c [452:532]
50 lines of code
13 McCabe index (conditional complexity)

int H3_EXPORT(hexRangeDistances)(H3Index origin, int k, H3Index* out,
                                 int* distances) {
    // Return codes:
    // 1 Pentagon was encountered
    // 2 Pentagon distortion (deleted k subsequence) was encountered
    // Pentagon being encountered is not itself a problem; really the deleted
    // k-subsequence is the problem, but for compatibility reasons we fail on
    // the pentagon.

    // k must be >= 0, so origin is always needed
    int idx = 0;
    out[idx] = origin;
    if (distances) {
        distances[idx] = 0;
    }
    idx++;

    if (H3_EXPORT(h3IsPentagon)(origin)) {
        // Pentagon was encountered; bail out as user doesn't want this.
        return HEX_RANGE_PENTAGON;
    }

    // 0 < ring <= k, current ring
    int ring = 1;
    // 0 <= direction < 6, current side of the ring
    int direction = 0;
    // 0 <= i < ring, current position on the side of the ring
    int i = 0;
    // Number of 60 degree ccw rotations to perform on the direction (based on
    // which faces have been crossed.)
    int rotations = 0;

    while (ring <= k) {
        if (direction == 0 && i == 0) {
            // Not putting in the output set as it will be done later, at
            // the end of this ring.
            origin =
                h3NeighborRotations(origin, NEXT_RING_DIRECTION, &rotations);
            if (origin == 0) {  // LCOV_EXCL_BR_LINE
                // Should not be possible because `origin` would have to be a
                // pentagon
                return HEX_RANGE_K_SUBSEQUENCE;  // LCOV_EXCL_LINE
            }

            if (H3_EXPORT(h3IsPentagon)(origin)) {
                // Pentagon was encountered; bail out as user doesn't want this.
                return HEX_RANGE_PENTAGON;
            }
        }

        origin = h3NeighborRotations(origin, DIRECTIONS[direction], &rotations);
        if (origin == 0) {  // LCOV_EXCL_BR_LINE
            // Should not be possible because `origin` would have to be a
            // pentagon
            return HEX_RANGE_K_SUBSEQUENCE;  // LCOV_EXCL_LINE
        }
        out[idx] = origin;
        if (distances) {
            distances[idx] = ring;
        }
        idx++;

        i++;
        // Check if end of this side of the k-ring
        if (i == ring) {
            i = 0;
            direction++;
            // Check if end of this ring.
            if (direction == 6) {
                direction = 0;
                ring++;
            }
        }

        if (H3_EXPORT(h3IsPentagon)(origin)) {
            // Pentagon was encountered; bail out as user doesn't want this.
            return HEX_RANGE_PENTAGON;
        }
    }
    return HEX_RANGE_SUCCESS;
}