对于Delphi2010字符串(UnicodeString)，是否有Boyer-Moore字符串搜索、快速搜索和替换功能以及快速字符串计数功能？

Question

我需要三个大字符串的快速函数:快速搜索、快速搜索和替换，以及快速计算字符串中的子字符串。

我在C++和Python中遇到过Boyer-Moore字符串搜索，但我找到的唯一用于实现快速搜索和替换的Delphi Boyer-Moore算法是Peter Morris的FastStrings的一部分，他的网站和电子邮件不再起作用。

我已经在Delphi2009/ 2010中移植了FastStrings，以便在AnsiStrings上很好地工作，其中一个字节等于一个AnsiChar，但在Delphi2010中让它们也能处理字符串(UnicodeString)似乎不是一件容易的事情。

使用这种Boyer-Moore算法，应该可以轻松地进行不区分大小写的搜索，以及不区分大小写的搜索和替换，而不需要任何临时字符串(使用StrUpper等)，也不需要调用Pos()，当需要对同一文本进行重复搜索时，Pos()比Boyer-Moore搜索慢。

(编辑:我有一个部分的解决方案，作为这个问题的答案，它几乎是100%完成的，它甚至有一个快速的字符串替换功能。我相信它肯定有bug，尤其是认为既然它假装具有Unicode能力，那么它一定是由于Unicode承诺未实现而出现了故障。)

(堆栈:有趣且出乎意料的结果；下面代码中的Edit2- SkipTable上的unicode代码点表的堆栈大小严重影响了您在unicode string boyer-moore字符串搜索中可以进行的双赢优化的数量。感谢Florent Ouchet指出了我应该立即注意到的事情。)

Answer 1

这个答案现在是完整的，适用于区分大小写的模式，但不适用于不区分大小写的模式，而且可能还有其他错误，因为它没有经过良好的单元测试，并且可能还可以进一步优化，例如，我重复了本地函数__SameChar，而不是使用比较函数回调，这样会更快，实际上，对于想要提供一些额外逻辑(某些语言的Unicode字形的等效集合)的Unicode用户来说，允许用户传入所有这些的比较函数将是非常好的。

基于Dorin Dominica的代码，我构建了以下代码。

{ _FindStringBoyer:
  Boyer-Moore search algorith using regular String instead of AnsiSTring, and no ASM.
  Credited to Dorin Duminica.
}
function _FindStringBoyer(const sString, sPattern: string;
  const bCaseSensitive: Boolean = True; const fromPos: Integer = 1): Integer;

    function __SameChar(StringIndex, PatternIndex: Integer): Boolean;
    begin
      if bCaseSensitive then
        Result := (sString[StringIndex] = sPattern[PatternIndex])
      else
        Result := (CompareText(sString[StringIndex], sPattern[PatternIndex]) = 0);
    end; // function __SameChar(StringIndex, PatternIndex: Integer): Boolean;

var
  SkipTable: array [Char] of Integer;
  LengthPattern: Integer;
  LengthString: Integer;
  Index: Integer;
  kIndex: Integer;
  LastMarker: Integer;
  Large: Integer;
  chPattern: Char;
begin
  if fromPos < 1 then
    raise Exception.CreateFmt('Invalid search start position: %d.', [fromPos]);
  LengthPattern := Length(sPattern);
  LengthString := Length(sString);
  for chPattern := Low(Char) to High(Char) do
    SkipTable[chPattern] := LengthPattern;
  for Index := 1 to LengthPattern -1 do
    SkipTable[sPattern[Index]] := LengthPattern - Index;
  Large := LengthPattern + LengthString + 1;
  LastMarker := SkipTable[sPattern[LengthPattern]];
  SkipTable[sPattern[LengthPattern]] := Large;
  Index := fromPos + LengthPattern -1;
  Result := 0;
  while Index <= LengthString do begin
    repeat
      Index := Index + SkipTable[sString[Index]];
    until Index > LengthString;
    if Index <= Large then
      Break
    else
      Index := Index - Large;
    kIndex := 1;
    while (kIndex < LengthPattern) and __SameChar(Index - kIndex, LengthPattern - kIndex) do
      Inc(kIndex);
    if kIndex = LengthPattern then begin
      // Found, return.
      Result := Index - kIndex + 1;
      Index := Index + LengthPattern;
      exit;
    end else begin
      if __SameChar(Index, LengthPattern) then
        Index := Index + LastMarker
      else
        Index := Index + SkipTable[sString[Index]];
    end; // if kIndex = LengthPattern then begin
  end; // while Index <= LengthString do begin
end;

{ Written by Warren, using the above code as a starter, we calculate the SkipTable once, and then count the number of instances of
  a substring inside the main string, at a much faster rate than we
  could have done otherwise.  Another thing that would be great is
  to have a function that returns an array of find-locations,
  which would be way faster to do than repeatedly calling Pos.
}
function _StringCountBoyer(const aSourceString, aFindString : String; Const CaseSensitive : Boolean = TRUE) : Integer;
var
  foundPos:Integer;
  fromPos:Integer;
  Limit:Integer;
  guard:Integer;
  SkipTable: array [Char] of Integer;
  LengthPattern: Integer;
  LengthString: Integer;
  Index: Integer;
  kIndex: Integer;
  LastMarker: Integer;
  Large: Integer;
  chPattern: Char;
    function __SameChar(StringIndex, PatternIndex: Integer): Boolean;
    begin
      if CaseSensitive then
        Result := (aSourceString[StringIndex] = aFindString[PatternIndex])
      else
        Result := (CompareText(aSourceString[StringIndex], aFindString[PatternIndex]) = 0);
    end; // function __SameChar(StringIndex, PatternIndex: Integer): Boolean;

begin
  result := 0;
  foundPos := 1;
  fromPos := 1;
  Limit := Length(aSourceString);
  guard := Length(aFindString);
  Index := 0;
  LengthPattern := Length(aFindString);
  LengthString := Length(aSourceString);
  for chPattern := Low(Char) to High(Char) do
    SkipTable[chPattern] := LengthPattern;
  for Index := 1 to LengthPattern -1 do
    SkipTable[aFindString[Index]] := LengthPattern - Index;
  Large := LengthPattern + LengthString + 1;
  LastMarker := SkipTable[aFindString[LengthPattern]];
  SkipTable[aFindString[LengthPattern]] := Large;
  while (foundPos>=1) and (fromPos < Limit) and (Index<Limit) do begin

    Index := fromPos + LengthPattern -1;
    if Index>Limit then
        break;
    kIndex := 0;
    while Index <= LengthString do begin
      repeat
        Index := Index + SkipTable[aSourceString[Index]];
      until Index > LengthString;
      if Index <= Large then
        Break
      else
        Index := Index - Large;
      kIndex := 1;
      while (kIndex < LengthPattern) and __SameChar(Index - kIndex, LengthPattern - kIndex) do
        Inc(kIndex);
      if kIndex = LengthPattern then begin
        // Found, return.
        //Result := Index - kIndex + 1;
        Index := Index + LengthPattern;
        fromPos := Index;
        Inc(Result);
        break;
      end else begin
        if __SameChar(Index, LengthPattern) then
          Index := Index + LastMarker
        else
          Index := Index + SkipTable[aSourceString[Index]];
      end; // if kIndex = LengthPattern then begin
    end; // while Index <= LengthString do begin

  end;
end; 

这确实是一个很好的算法，因为：

• 以这种方式计算字符串Y中的子串X的实例要快得多，这是惊人的。
• 仅仅替换了Pos()，_FindStringBoyer()比FastCode项目人员贡献给Delphi的纯asm版本的Pos()更快，目前用于Pos，如果你需要区分大小写，你可以想象当我们不需要对100兆字节的字符串调用UpperCase时，性能会有多大的提升。(好的，您的字符串不会那么大。但是，高效的算法仍然是一件美丽的事情。)

好的，我写了一个Boyer-Moore风格的字符串替换：

function _StringReplaceBoyer(const aSourceString, aFindString,aReplaceString : String; Flags: TReplaceFlags) : String;
var
  errors:Integer;
  fromPos:Integer;
  Limit:Integer;
  guard:Integer;
  SkipTable: array [Char] of Integer;
  LengthPattern: Integer;
  LengthString: Integer;
  Index: Integer;
  kIndex: Integer;
  LastMarker: Integer;
  Large: Integer;
  chPattern: Char;
  CaseSensitive:Boolean;
  foundAt:Integer;
  lastFoundAt:Integer;
  copyStartsAt:Integer;
  copyLen:Integer;
    function __SameChar(StringIndex, PatternIndex: Integer): Boolean;
    begin
      if CaseSensitive then
        Result := (aSourceString[StringIndex] = aFindString[PatternIndex])
      else
        Result := (CompareText(aSourceString[StringIndex], aFindString[PatternIndex]) = 0);
    end; // function __SameChar(StringIndex, PatternIndex: Integer): Boolean;

begin
  result := '';
  lastFoundAt := 0;
  fromPos := 1;
  errors := 0;
  CaseSensitive := rfIgnoreCase in Flags;
  Limit := Length(aSourceString);
  guard := Length(aFindString);
  Index := 0;
  LengthPattern := Length(aFindString);
  LengthString := Length(aSourceString);
  for chPattern := Low(Char) to High(Char) do
    SkipTable[chPattern] := LengthPattern;
  for Index := 1 to LengthPattern -1 do
    SkipTable[aFindString[Index]] := LengthPattern - Index;
  Large := LengthPattern + LengthString + 1;
  LastMarker := SkipTable[aFindString[LengthPattern]];
  SkipTable[aFindString[LengthPattern]] := Large;
  while (fromPos>=1) and (fromPos <= Limit) and (Index<=Limit) do begin

    Index := fromPos + LengthPattern -1;
    if Index>Limit then
        break;
    kIndex := 0;
    foundAt := 0;
    while Index <= LengthString do begin
      repeat
        Index := Index + SkipTable[aSourceString[Index]];
      until Index > LengthString;
      if Index <= Large then
        Break
      else
        Index := Index - Large;
      kIndex := 1;
      while (kIndex < LengthPattern) and __SameChar(Index - kIndex, LengthPattern - kIndex) do
        Inc(kIndex);
      if kIndex = LengthPattern then begin


        foundAt := Index - kIndex + 1;
        Index := Index + LengthPattern;
        //fromPos := Index;
        fromPos := (foundAt+LengthPattern);
        if lastFoundAt=0 then begin
                copyStartsAt := 1;
                copyLen := foundAt-copyStartsAt;
        end else begin
                copyStartsAt := lastFoundAt+LengthPattern;
                copyLen := foundAt-copyStartsAt;
        end;

        if (copyLen<=0)or(copyStartsAt<=0) then begin
                Inc(errors);
        end;

        Result := Result + Copy(aSourceString, copyStartsAt, copyLen ) + aReplaceString;
        lastFoundAt := foundAt;
        if not (rfReplaceAll in Flags) then
                 fromPos := 0; // break out of outer while loop too!
        break;
      end else begin
        if __SameChar(Index, LengthPattern) then
          Index := Index + LastMarker
        else
          Index := Index + SkipTable[aSourceString[Index]];
      end; // if kIndex = LengthPattern then begin
    end; // while Index <= LengthString do begin
  end;
  if (lastFoundAt=0) then
  begin
     // nothing was found, just return whole original string
      Result := aSourceString;
  end
  else
  if (lastFoundAt+LengthPattern < Limit) then begin
     // the part that didn't require any replacing, because nothing more was found,
     // or rfReplaceAll flag was not specified, is copied at the
     // end as the final step.
    copyStartsAt := lastFoundAt+LengthPattern;
    copyLen := Limit; { this number can be larger than needed to be, and it is harmless }
    Result := Result + Copy(aSourceString, copyStartsAt, copyLen );
  end;

end;

好的，问题是:堆栈占用的空间：

var
  skiptable : array [Char] of Integer;  // 65536*4 bytes stack usage on Unicode delphi

再见CPU地狱，你好堆栈地狱。如果我使用动态数组，那么我必须在运行时调整它的大小。所以这个东西基本上是快的，因为你计算机上的虚拟内存系统在堆栈上256K的时候不会闪烁，但这并不总是一段最优的代码。尽管如此，我的电脑在这样的大堆东西面前是不会眨眼的。它不会成为Delphi标准库的默认值，也不会在未来赢得任何快速代码挑战，因为它只占用了一定的空间。我认为重复搜索是一种情况，上面的代码应该写成一个类，skiptable应该是那个类中的一个数据字段。然后，您可以构建boyer-moore表一次，并且随着时间的推移，如果字符串是不变的，则重复使用该对象进行快速查找。

Answer 2

因为我只是在寻找同样的东西: Jedi JCL已经在jclUnicode.pas中使用Boyer-Moore获得了一个支持unicode的搜索引擎。我还不知道它有多好或者有多快。