Is it possible to raise a Decimal to an integer power in .NET?

Question

I'm in .NET (C#), and I have a piece of code that basically does the following:

decimal value = decimal.Parse(s);
long result = (long)(value * 10000M);

However, I can't use 10000 directly since the number of decimal places is variable (in this case, it's stored as 4). Is there a way I can use this 4 to get to 10000M?

I was thinking on something like Math.Pow, but it doesn't seem to be available for decimal types. I was also thinking on a simple function that does multiplication in a loop, but if something already exists in the .NET framework, then I'd rather use that.

You can use `Math.Pow` and then case the result to `decimal`. — MarcinJuraszek, Apr 13 '15 at 00:59
@Kevin, you're right. Maybe it's simpler than I thought initially — Arturo Torres Sánchez, Apr 13 '15 at 01:03
@ArturoTorresSánchez because even if it existed it wouldn't make sense http://stackoverflow.com/questions/6425501/is-there-a-math-api-for-powdecimal-decimal — Xi Sigma, Apr 13 '15 at 01:05

score 2 · Answer 1 · answered Apr 13 '15 at 02:07

Here's a simple method to raise a decimal to a non-negative integer power.

public static decimal Pow( decimal x, int n )
{
    if( n < 0 )
    {
        throw new ArgumentOutOfRangeException( "n" );
    }

    decimal result = 1;
    decimal multiplier = x;

    while( n > 0 )
    {
        if( ( n & 1 ) > 0 ) result *= multiplier;
        multiplier *= multiplier;
        n >>= 1;
    }

    return result;
}

druidicwyrm · Answer 2 · 2015-04-13T02:00:23.537

1

I don't like to use Math.Pow because it uses a generic math equation, and so is often slower (unless you are using fractional exponents which it looks like you are not). Instead I would write an extension method like this:

public static long ToPower(this decimal val, int pow)
{
    decimal ret = 1;
    for(int i = 0; i < pow; i++)
        ret *= val;
    return (long)ret;
}

Which can be called like:

myDecimal.ToPower(4);

EDIT: I just ran a test to validate times. It seems that Math.Pow is now faster than a basic loop for any integer power above 50. The times are minimal, but often times when I am doing power math, I am doing a lot of calculations.

If you are doing this calculation a few times, then there is no need to use anything but Math.Pow as the performance changes are minimal.

edited Apr 13 '15 at 02:00

answered Apr 13 '15 at 01:10

druidicwyrm

480
2
11

The question was about doing it with decimals. – siride Apr 13 '15 at 01:47
I updated the code to use a decimal for the value. However, that was a rather trivial change. The code only shows taking a decimal to an integer power, and that seems to be what the OP is asking for. – druidicwyrm Apr 13 '15 at 02:00
I didn't downvote. That was just my most reasonable guess as to the downvote. – siride Apr 13 '15 at 13:17
I see. I wasn't upset, just confused really. Thanks for the suggestion though. – druidicwyrm Apr 13 '15 at 14:36

score 1 · Answer 3 · answered Apr 13 '15 at 04:56

1

Just cast it to a decimal after raising it to the power.

decimal value = decimal.Parse(s);
int power = 4;
long result = (long)(value * (decimal)Math.Pow(10, power));

answered Apr 13 '15 at 04:56

Alex Wiese

8,142
6
42
71

Is it possible to raise a Decimal to an integer power in .NET?

3 Answers3