Look for specified sequence in stream

[WojTec]

Zitat von CCRDude:

Since the key word used here was fast, I would recommend something like Boyer Moore. And if it's more than one sequence to look for, Aho-Corasick.

Wow, I didn't know about Boyer-Moore and Aho-Corasick, but as I see I go in right direction, because what I tried to do was similar to BM

Zitat von CCRDude:

Typical implementations of these algorithms should already include stream functionality.

Do you know some? I found for strings, but as I understand is applicable for any data where need to find sequence.

Zitat von Union:

You should eliminate object access there by copying the values to local variables.

For performance?

Delphi-Quellcode:

function OffsetsLookup(const AStream: TStream; const APattern: TBytes): TOffsets; overload;
var
  Position, Size, Offset: int64;
  PatternLen, MaxPosition: Int64;
  Memory: TMemoryStream;
  MemoryPtr: Pointer;
  Buffer: Byte;
begin
  SetLength(Result, 0);

  Memory := TMemoryStream.Create;
  try
    Memory.CopyFrom(AStream, 0);
    Memory.Position := 0;

    // Work only with variables to eliminate Object access
    MemoryPtr := Memory.Memory;
    Position := Memory.Position;
    Size := Memory.Size;
    PatternLen := Length(APattern);

    // No calculation of end condition
    MaxPosition := Size - PatternLen + 1;

    while Position < MaxPosition do
    begin
      Offset := Position;
      Buffer := Byte(Pointer(Longint(MemoryPtr) + Offset)^);

      // ????? :(
    end;
  finally
    Memory.Free;
  end;
end;

And don't know how to operate on raw binary data. I found these implementations for strings:

Code:

http://www.delphigeist.com/2009/10/boyer-moore-horspool-algorithm.html
http://www.delphigeist.com/2011/05/boyer-moore-horspool-return-all.html <-- this looking good
http://www.delphigeist.com/2010/04/boyer-moore-horspool-in-delphi-2010.html

Don't know how to apply for streams in above function

BTW: what's the difference between Boyer-Moore and Boyer-Moore-Horspool? I read in Wikipedia, but don't understan, for me is the same