upd placed my version in the description at the end
I need to convert mantissa and exponent to decimal. This is how I coded that:
// long field.Decimal.Mantissa
// sbyte field.Decimal.Exponent
decimal MDEntryPx = field.Decimal.Mantissa * (decimal)(Math.Pow(10, field.Decimal.Exponent));
field.Decimal.Mantissa
is integer
but Math.Pow(10, field.Decimal.Exponent)
is double so I afraid that I can lost precision when casting to decimal.
Should I write my own Pow
function for integer
types that will produce decimal
?
What would you suggest? I care about perfomance as I call this functions dozen of thousands times per second! So ugly but fast solutions are highly desired!
And I care about precision as I'm working with money here.
This is what I've just coded, but probably someone can suggest something better:
class Util
{
private static readonly decimal[] posPow10 = {
1M,
10M,
100M,
1000M,
10000M,
100000M,
1000000M,
10000000M,
100000000M,
1000000000M,
10000000000M,
100000000000M
};
private static readonly decimal[] negPow10 = {
1M,
0.1M,
0.01M,
0.001M,
0.0001M,
0.00001M,
0.000001M,
0.0000001M,
0.00000001M,
0.000000001M,
0.0000000001M,
0.00000000001M,
};
public static decimal Pow(decimal mantissa, sbyte exponent)
{
decimal result = mantissa;
if (exponent >= 0)
{
result *= posPow10[exponent];
} else {
result *= negPow10[-exponent];
}
return result;
}
}
There is a constructor of decimal
that does pretty much what you want. But it uses the internal representation of decimal
, which is different from your representation. The conversion should be pretty simple for numbers with negative exponent
, since you can directly translate that into the scale
parameter of the constructor. But with positive exponent
, I think you will need to do the multiplication by yourself.
Although I have no idea whether it would be actually faster than your code. And it would be certainly much less readable, so your solution might be fine.
来源:https://stackoverflow.com/questions/9993417/convert-long-mantissa-and-sbyte-exponent-to-decimal