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@pedoc pedoc/BoyerMoore.cs forked from mjs3339/BoyerMoore.cs
Created Oct 24, 2018

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C# High Performance Boyer Moore Byte Array Search Algorithm
public class BoyerMoore
{
private int[] _jumpTable;
private byte[] _pattern;
private int _patternLength;
public BoyerMoore()
{
}
public BoyerMoore(byte[] pattern)
{
_pattern = pattern;
_jumpTable = new int[256];
_patternLength = _pattern.Length;
for(var index = 0; index < 256; index++)
_jumpTable[index] = _patternLength;
for(var index = 0; index < _patternLength - 1; index++)
_jumpTable[_pattern[index]] = _patternLength - index - 1;
}
public void SetPattern(byte[] pattern)
{
_pattern = pattern;
_jumpTable = new int[256];
_patternLength = _pattern.Length;
for(var index = 0; index < 256; index++)
_jumpTable[index] = _patternLength;
for(var index = 0; index < _patternLength - 1; index++)
_jumpTable[_pattern[index]] = _patternLength - index - 1;
}
public unsafe int Search(byte[] searchArray, int startIndex = 0)
{
if(_pattern == null)
throw new Exception("Pattern has not been set.");
if(_patternLength > searchArray.Length)
throw new Exception("Search Pattern length exceeds search array length.");
var index = startIndex;
var limit = searchArray.Length - _patternLength;
var patternLengthMinusOne = _patternLength - 1;
fixed(byte* pointerToByteArray = searchArray)
{
var pointerToByteArrayStartingIndex = pointerToByteArray + startIndex;
fixed(byte* pointerToPattern = _pattern)
{
while(index <= limit)
{
var j = patternLengthMinusOne;
while(j >= 0 && pointerToPattern[j] == pointerToByteArrayStartingIndex[index + j])
j--;
if(j < 0)
return index;
index += Math.Max(_jumpTable[pointerToByteArrayStartingIndex[index + j]] - _patternLength + 1 + j, 1);
}
}
}
return-1;
}
public unsafe List<int> SearchAll(byte[] searchArray, int startIndex = 0)
{
var index = startIndex;
var limit = searchArray.Length - _patternLength;
var patternLengthMinusOne = _patternLength - 1;
var list = new List<int>();
fixed(byte* pointerToByteArray = searchArray)
{
var pointerToByteArrayStartingIndex = pointerToByteArray + startIndex;
fixed(byte* pointerToPattern = _pattern)
{
while(index <= limit)
{
var j = patternLengthMinusOne;
while(j >= 0 && pointerToPattern[j] == pointerToByteArrayStartingIndex[index + j])
j--;
if(j < 0)
list.Add(index);
index += Math.Max(_jumpTable[pointerToByteArrayStartingIndex[index + j]] - _patternLength + 1 + j, 1);
}
}
}
return list;
}
public int SuperSearch(byte[] searchArray, int nth, int start = 0)
{
var e = start;
var c = 0;
do
{
e = Search(searchArray, e);
if(e == -1)
return-1;
c++;
e++;
} while(c < nth);
return e - 1;
}
}
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