int.ToString("0000")の置き換え

IntToStringUtil.cs

public static class IntToStringUtil
{
    public static string Padding0(int n, int d)
    {
        char[] c = new char[n < 0 ? d + 1 : d];
        int s = 0;
        if (n < 0)
        {
            c[0] = '-';
            n *= -1;
            s = 1;
        }
        for (int i = d + s - 1; i >= s; i--)
        {
            if (n > 0)
            {
                c[i] = (char)(n % 10 + '0');
                n /= 10;
            }
            else
            {
                c[i] = '0';
            }
        }
        return new string(c);
    }
}

UnsafeIntToStringUtil.cs

public static class UnsafeIntToStringUtil
{
    public static string Padding0(int n, int d)
    {
        unsafe
        {
            char* c = stackalloc char[11];
            int s = 0;
            if (n < 0)
            {
                c[0] = '-';
                n *= -1;
                s = 1;
            }
            for (int i = d + s - 1; i >= s; i--)
            {
                if (n > 0)
                {
                    c[i] = (char)(n % 10 + '0');
                    n /= 10;
                }
                else
                {
                    c[i] = '0';
                }
            }
            return new string(c, 0, d + s);
        }
    }
}