Reducing large numbers in Unity3D. How to do it?

Question

C++ / C#

There is a number of type decimal in C#.
Conditionally 1,000,000,000,000
It is desirable to display it in the form of 1T (Trilion), while it is desirable that there be the possibility of such a display:
1,250,000,000,000 = 1.25T
I have already rummaged through many articles, but have not found a solution.
How can such a reduction be implemented?
1000 = 1K || 1 250 = 1.25K
1 000 000 = 1M || 1,250,000 = 1.25M
etc.
Everything I could find, but it doesn't work very well.

char[] names = { 'K', 'M', 'B', 'T', ...};
    private string __CutDigit(string digit)
    {
        var dotIdx = digit.IndexOf('.');
        if (dotIdx < 0) dotIdx = digit.Length;
        var triples = dotIdx / 3;
        var num = dotIdx % 3;

        return digit.Substring(0, num) + '.' + digit[num] + names[triples];
    }

Answer 1

static string[] names = { "", "K", "M", "B", "T" };
  
static string FormatMoney(decimal digit)
{
  int n = 0;
  while (n + 1 < names.Length && digit >= 100m)
  {
    digit /= 1000m;
    n++;
  }
  return string.Format("{0}{1}", digit, names[n]);
}

Counting digit >= 100m can result in numbers like 0.11K or 0.25M.
If fractional numbers are needed only greater than 1, then the comparison must be done with 1000.