src/vs/editor/common/model/prefixSumComputer.ts/PrefixSumComputer/getPrefixSum
class PrefixSumComputer:	public getPrefixSum(index: number): number {
		if (index < 0) {
			return 0;
		}

		index = toUint32(index);
		return this._getPrefixSum(index);
	}