// Differentially encode a sequence of numbers into V. The starting value and
// terminating 0 are not added to V, so it will have the same size as List.
+static
DiffVec &diffEncode(DiffVec &V, unsigned InitVal, ArrayRef<unsigned> List) {
assert(V.empty() && "Clear DiffVec before diffEncode.");
uint16_t Val = uint16_t(InitVal);