int H3_EXPORT()

in src/h3lib/lib/algos.c [572:638]
44 lines of code
13 McCabe index (conditional complexity)

int H3_EXPORT(hexRing)(H3Index origin, int k, H3Index* out) {
    // Short-circuit on 'identity' ring
    if (k == 0) {
        out[0] = origin;
        return 0;
    }
    int idx = 0;
    // Number of 60 degree ccw rotations to perform on the direction (based on
    // which faces have been crossed.)
    int rotations = 0;
    // Scratch structure for checking for pentagons
    if (H3_EXPORT(h3IsPentagon)(origin)) {
        // Pentagon was encountered; bail out as user doesn't want this.
        return HEX_RANGE_PENTAGON;
    }

    for (int ring = 0; ring < k; 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)) {
            return HEX_RANGE_PENTAGON;
        }
    }

    H3Index lastIndex = origin;

    out[idx] = origin;
    idx++;

    for (int direction = 0; direction < 6; direction++) {
        for (int pos = 0; pos < k; pos++) {
            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
            }

            // Skip the very last index, it was already added. We do
            // however need to traverse to it because of the pentagonal
            // distortion check, below.
            if (pos != k - 1 || direction != 5) {
                out[idx] = origin;
                idx++;

                if (H3_EXPORT(h3IsPentagon)(origin)) {
                    return HEX_RANGE_PENTAGON;
                }
            }
        }
    }

    // Check that this matches the expected lastIndex, if it doesn't,
    // it indicates pentagonal distortion occurred and we should report
    // failure.
    if (lastIndex != origin) {
        return HEX_RANGE_PENTAGON;
    } else {
        return HEX_RANGE_SUCCESS;
    }
}