Quantize
Returns the arithmetic value of the first parameter, with the exponent adjusted to match the second parameter, using a specified rounding mode.
_Decimal64 __d64_quantize (_Decimal64, _Decimal64, long rounding_mode);
_Decimal128 __d128_quantize (_Decimal128, _Decimal128, long rounding_mode);
These functions temporarily override the rounding mode in effect for the current operation.