Decimal.compareOp

typeof(this) compareOp(
          const  typeof(
          this)  rhs,
          ref  DecimalContext ctx)

const @safe pure nothrow @nogc

IEEE compare under an explicit context: returns -1, 0 or 1 as a decimal value, or a quiet NaN carrying the left operand's sign when either operand is NaN (signaling NaNs signal INVALID_OPERATION); numerical comparison otherwise (±∞ and ±0 per the usual total rules on numbers).