 Reader Bernie submits for our approval this wonderful C# log base 2 implementation. He says: “We can distinguish two halves in that code. It looks like it was originally written for an unsigned 16-bit int, and later on extended for signed 32-bit integers.”

This code reminds me of the change-sorting machine I have in my closet, which sorts change based on weight. That thing has no error handling if you try to sort, say, a huge boulder through it; it'd just fall apart. At least here, we have the assurance that the universe's biggest numbers all have a log base 2 of 31.

``````public static int Log2(int x)
{
if (x <= 65536)
{
if (x <= 256)
{
if (x <= 16)
{
if (x <= 4)
{
if (x <= 2)
{
if (x <= 1)
return 0;
return 1;
}

return 2;
}

if (x <= 8)
return 3;
return 4;
}

if (x <= 64)
{
if (x <= 32)
return 5;
return 6;
}

if (x <= 128)
return 7;
return 8;
}

if (x <= 4096)
{
if (x <= 1024)
{
if (x <= 512)
return 9;
return 10;
}

if (x <= 2048)
return 11;
return 12;
}

if (x <= 16384)
{
if (x <= 8192)
return 13;
return 14;
}

if (x <= 32768)
return 15;
return 16;
}

if (x <= 16777216)
{
if (x <= 1048576)
{
if (x <= 262144)
{
if (x <= 131072)
return 17;
return 18;
}

if (x <= 524288)
return 19;
return 20;
}

if (x <= 4194304)
{
if (x <= 2097152)
return 21;
return 22;
}

if (x <= 8388608)
return 23;
return 24;
}

if (x <= 268435456)
{
if (x <= 67108864)
{
if (x <= 33554432)
return 25;
return 26;
}

if (x <= 134217728)
return 27;
return 28;
}

if (x <= 1073741824)
{
if (x <= 536870912)
return 29;
return 30;
}

return 31;
}
```
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