I too was looking for a fast way to convert decimal number to another base in the range of [2..36] so I developed the following code. Its simple to follow and uses a Stringbuilder object as a proxy for a character buffer that we can index character by character. The code appears to be very fast compared to alternatives and a lot faster than initialising individual characters in a character array.
For your own use you might prefer to: 1/ Return a blank string rather than throw an exception. 2/ remove the radix check to make the method run even faster 3/ Initialise the Stringbuilder object with 32 '0's and remove the the line result.Remove( 0, i );. This will cause the string to be returned with leading zeros and further increase the speed. 4/ Make the Stringbuilder object a static field within the class so no matter how many times the DecimalToBase method is called the Stringbuilder object is only initialised the once. If you do this change 3 above would no longer work.
I hope someone finds this useful :)
AtomicParadox
static string DecimalToBase(int number, int radix)
{
// Check that the radix is between 2 and 36 inclusive
if ( radix < 2 || radix > 36 )
throw new ArgumentException("ConvertToBase(int number, int radix) - Radix must be between 2 and 36.");
// Create a buffer large enough to hold the largest int value represented in binary digits
StringBuilder result = new StringBuilder(" "); // 32 spaces
// The base conversion calculates the digits in reverse order so use
// an index to point to the last unused space in our buffer
int i = 32;
// Convert the number to the new base
do
{
int remainder = number % radix;
number = number / radix;
if(remainder <= 9)
result[--i] = (char)(remainder + '0'); // Converts [0..9] to ASCII ['0'..'9']
else
result[--i] = (char)(remainder + '7'); // Converts [10..36] to ASCII ['A'..'Z']
} while ( number > 0 );
// Remove the unwanted padding from the front of our buffer and return the result
// Note i points to the last unused character in our buffer
result.Remove( 0, i );
return (result.ToString());
}