C#

class General<br />
{<br />
     class ClassA<br />
     {<br />
         public string name;<br />
<br />
         public ClassA(string nm) { this.name = nm; }<br />
     }<br />
<br />
     static void Main(string[] args)<br />
     {<br />
         List<ClassA> listOne = new List<ClassA>();<br />
         List<ClassA> listTwo = new List<ClassA>();<br />
<br />
         ClassA a = new ClassA("A");<br />
         ClassA b = new ClassA("B");<br />
         ClassA c = new ClassA("C");<br />
         ClassA d = new ClassA("D");<br />
         ClassA e = new ClassA("E");<br />
<br />
         listOne.AddRange(new ClassA[] { a, b, c, d, e });<br />
         listTwo.AddRange(new ClassA[] { a, c, d });<br />
<br />
         string msg = "Start Length of listOne: " +<br />
             listOne.Count.ToString() +<br />
             "\nStart Length of listTwo: " +<br />
             listTwo.Count.ToString() +<br />
             "\nWhat is removed:\n";<br />
         foreach (ClassA z in listTwo)<br />
         {<br />
             msg += z.name + "\t";<br />
             listOne.Remove(z);<br />
         }<br />
<br />
         Console.WriteLine(msg + "\nLength of listOne: " +<br />
             listOne.Count.ToString() +<br />
             "\nLength of listTwo: " +<br />
             listTwo.Count.ToString());<br />
     }<br />
}<br />

AndrusM wrote:

You wrote that this code modifies same collection inside foreach loop which is not allowed.
.NET does not throw exception for this code.
So it is .NET bug, isn't it ?

Skippums wrote:

like perhaps a binary search algorithm?

private byte Log2_2(uint val) {
    if (val < 1)
        return byte.MaxValue;
    byte high = sizeof(uint) << 3;
    byte low  = 0, med = (byte)(high >> 1);
    uint tmp = val >> med;
    while (tmp != 1) {
        if (tmp == 0)
            high = med;
        else
            low  = med;
        med = (byte)(low + high >> 1);
        tmp = val >> med;
    }
    return med;
}

int LP_log2_3(uint val) {
    if(val==0) return -1;
    int res=0;
    if(val>0x0000FFFF) {res+=16;val>>=16;}
    if(val>0x000000FF) {res+=8;val>>=8;}
    if(val>0x0000000F) {res+=4;val>>=4;}
    if(val>0x00000003) {res+=2;val>>=2;}
    if(val>1) res++;
    return res;
}

                               Gross     Net
1. Linear search:             1542 ms  1091 ms
2. Binary search:              887 ms   436 ms
3. Hardcoded Conditionals:     686 ms   235 ms
4. Control (returns constant): 451 ms     0 ms

private Stopwatch sw = new Stopwatch();
private List<uint> m_Nums = new List<uint>(0x1000000);
private List<uint> result1 = new List<uint>(0x1000000);
private List<uint> result2 = new List<uint>(0x1000000);
private List<uint> result3 = new List<uint>(0x1000000);
private List<uint> result4 = new List<uint>(0x1000000);
...
private void button1_Click(object sender, EventArgs e) {
    m_Nums.Clear();
    result1.Clear();
    result2.Clear();
    result3.Clear();
    result4.Clear();
    Random rnd = new Random();
    for (int i = 0; i < m_Nums.Capacity; ++i)
        m_Nums.Add((uint)rnd.Next());
// Start "Block1"
    sw.Start();
    foreach (uint num in m_Nums)
        result1.Add(Log2_1(num));
    sw.Stop();
    label1.Text = sw.ElapsedMilliseconds.ToString();
    sw.Reset();
// End "Block1"
// Repeat "Block1" for methods Log2_2, Log2_3, and Log2_4
}

if (val < 1)
    return byte.MaxValue;
int shift = sizeof(uint) << 2;
uint mask = uint.MaxValue >> shift;
int rval = 0;
do {
    if (val > mask) {
        rval += shift;
        val >>= shift;
    }
    shift >>= 1;
    mask >>= shift;
} while (shift > 0);
return (byte)rval;