private int HighestBitSet(int bitPattern)
{
return
(Convert.ToString(bitPattern, 2).Length - 1)
-
Convert.ToString(bitPattern, 2).IndexOf("1");
}
[.net] HighestBitSet in C#
Author
I'm trying to optimize a a method that returns the highest bit set in a bit pattern, my current code is :
There are lots of optimizations you could do here.
The easiest would be to create a temp string to hold the results of Convert.ToString so you only do the conversion once.
Of course, a series of "if bitPattern && 0x... { return ... }" statements might be faster than the string conversion and search, but would require more code.
The easiest would be to create a temp string to hold the results of Convert.ToString so you only do the conversion once.
Of course, a series of "if bitPattern && 0x... { return ... }" statements might be faster than the string conversion and search, but would require more code.
Author
Author
Quote:Original post by VizOne
Take a look
Regards,
Andre
Ok this seems to work, now my problem is why ? :-)
I dont't understand the purpose of the two arrays, what's the meaning of the numbers in b and s ?
private static int HighestBitSet(int value) { int [] b = {0x2, 0xC, 0xF0, 0xFF00}; int [] s = {1, 2, 4, 8}; int i; int c = 0; // result of log2(v) will go here for (i = 3; i >= 0; i--) // unroll for speed... { if ((value & b) != 0) { value >>= s; c |= s; } } return c; }Update : does not work with Int32 max (2147483647), i think that it only works with an uint and that is not CLS compliant :-(
Update2 : Well I have made some tests and the method that uses a table is the fastest so i will stick with that one, anyway here's the code :
static int [] LogTable256 = { 0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7 }; private static int HighestBitSet3(int value) { int c = 0; // c will be lg(v) int t, tt; // temporaries if ((tt = value >> 16) != 0) { c = ((t = value >> 24) != 0) ? 24 + LogTable256[t] : 16 + LogTable256[tt & 0xFF]; } else { c = ((t = value >> 8) != 0) ? 8 + LogTable256[t] : LogTable256[value]; } return c; }[Edited by - Ivo Leitao on August 5, 2005 12:12:32 PM]
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