Circular shift Int32 digits using C#

Question

Members,

What I am trying to do is to right or left shift the digits of an Int32 (not the bits!!).

So if shift the constant:

123456789

by 3

I should get

789123456

So no digits get lost, because we talk about a circular shift. After a bit of testing I've come up with this method, which works:

static uint[] Pow10 = new uint[] { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, uint.MaxValue };
    static uint RotateShift10(uint value, int shift)
    {
        int r = (int)Math.Floor(Math.Log10(value) + 1);
        while (r < shift)
            shift = shift - r;
        if (shift < 0) shift = 9 + shift;
        uint x = value / Pow10[shift];
        uint i = 0;
        while (true)
        {
            if (x < Pow10[i])
                return x + (value % Pow10[shift]) * Pow10[i];
            i += 1;
        }
    }

The way I am looking for should be an arithmetic solution, not a string conversion and then the rotation. I also assume that:

• The Int32 value has no 0-digits in it, to prevent any loss of digits.
• The Int32 is a non-negative number
• A positive Rotation integer should shift to the right, and negative one to the left.

My algorithm already does all of that, and I like to know if there are way to tweak it a bit, if there is a better arithmetic solution to the problem?

Answer 1

Because I just can't resist a 'has to have an arithmetic approach' challenge :D , fiddled around with the following:

    static uint RotateShift(uint value, int shift)
    {
        int len = (int)Math.Log10(value) + 1;
        shift %= len;
        if (shift < 0) shift += len;            
        uint pow = (uint)Math.Pow(10, shift);
        return (value % pow) * (uint)Math.Pow(10, len - shift) + value / pow;
    }

---

edit Also some test results

foreach(var val in new uint[]{123456789, 12345678})
   foreach (var shift in new[] { 3, -3, 1, -1, 11, -11, 18 })
   {
      Console.WriteLine("Value {0} Shift {1} -> {2}", val, shift, RotateShift(val, shift));
   }

Value 123456789 Shift 3 -> 789123456
Value 123456789 Shift -3 -> 456789123
Value 123456789 Shift 1 -> 912345678
Value 123456789 Shift -1 -> 234567891
Value 123456789 Shift 11 -> 891234567
Value 123456789 Shift -11 -> 345678912
Value 123456789 Shift 18 -> 123456789
Value 12345678 Shift 3 -> 67812345
Value 12345678 Shift -3 -> 45678123
Value 12345678 Shift 1 -> 81234567
Value 12345678 Shift -1 -> 23456781
Value 12345678 Shift 11 -> 67812345
Value 12345678 Shift -11 -> 45678123
Value 12345678 Shift 18 -> 78123456