Function normalize_index

src/arithmetic/list_funcs/list_funcs.c:202–236

normalize index returns true if 'index' is in range: [0..array_len] false otherwise idx is 0-based when non-negative or from the end of the list when negative

// idx is 0-based when non-negative
// or from the end of the list when negative
static inline bool normalize_index
(
	int32_t *index,
	int32_t arrayLen,
	bool bounds_inclusive
) {
	int32_t idx = *index;

	if(bounds_inclusive) {
		// for the index normalization calculation to be correct when index is negative
		// for example index -1 on a 6 elements array should return the last
		// element index
		// [0,1,2,3,4,5][-1] = 5
		arrayLen += 1;
	}

	//--------------------------------------------------------------------------
	// check index bounds
	//--------------------------------------------------------------------------

	// index range can be [-arrayLen, arrayLen)
	// this is because 0 = arrayLen+(-arrayLen)
	if((idx < 0 && idx + arrayLen < 0) ||
	   (idx > 0 && idx >= arrayLen)) {
		return false;
	}

	// compute index
	if(idx < 0) {
		*index = arrayLen + idx;
	}

	// index within bounds
	return true;
}

// If given an array, returns a value in a specific index in an array.
//    Valid index range is [-arrayLen, arrayLen).