Round 函数
velox/functions/prestosql/Arithmetic.h
template <typename T>
struct RoundFunction {
template <typename TInput>
FOLLY_ALWAYS_INLINE void
call(TInput& result, const TInput& a, const int32_t b = 0) {
result = round(a, b);
}
};
/// Round function
/// When AlwaysRoundNegDec is false, presto semantics is followed which does not
/// round negative decimals for integrals and round it otherwise
/// Note that is is likely techinically impossible for this function to return
/// expected results in all cases as the loss of precision plagues it on both
/// paths: factor multiplication for large numbers and addition of truncated
/// number to the rounded fraction for small numbers
