'Returns a multiplied by b, plus c.
The first two operands are multiplied together, using multiply,
the third operand is then added to the result of that
multiplication, using add, all with only one final rounding.
>>> ExtendedContext.fma(Decimal(\'3\'), Decimal(\'5\'), Decimal(\'7\'))
Decimal(\'22\')
>>> ExtendedContext.fma(Decimal(\'3\'), Decimal(\'-5\'), Decimal(\'7\'))
Decimal(\'-8\')
>>> ExtendedContext.fma(Decimal(\'888565290\'), Decimal(\'1557.96930\'), Decimal(\'-86087.7578\'))
Decimal(\'1.38435736E+12\')
>>> ExtendedContext.fma(1, 3, 4)
Decimal(\'7\')
>>> ExtendedContext.fma(1, Decimal(3), 4)
Decimal(\'7\')
>>> ExtendedContext.fma(1, 3, Decimal(4))
Decimal(\'7\')'

def fma(self, a, b, c):

    a = _convert_other(a, raiseit=True)
    return a.fma(b, c, context=self)
