case insensitive Pos

Question

Is there any comparable function like Pos that is not case-sensitive in D2010 (unicode)?

I know I can use Pos(AnsiUpperCase(FindString), AnsiUpperCase(SourceString)) but that adds a lot of processing time by converting the strings to uppercase every time the function is called.

For example, on a 1000000 loop, Pos takes 78ms while converting to uppercase takes 764ms.

str1 := 'dfkfkL%&/s"#<.676505';
  for i := 0 to 1000000 do
    PosEx('#<.', str1, 1); // Takes 78ms

  for i := 0 to 1000000 do
    PosEx(AnsiUpperCase('#<.'), AnsiUpperCase(str1), 1); // Takes 764ms

I know that to improve the performance of this specific example I can convert the strings to uppercase first before the loop, but the reason why I'm looking to have a Pos-like function that is not case-sensitive is to replace one from FastStrings. All the strings I'll be using Pos for will be different so I will need to convert each and every one to uppercase.

Is there any other function that might be faster than Pos + convert the strings to uppercase?

Answer 1

Why not just convert the both the substring and the source string to lower or upper case within the regular Pos statement. The result will effectively be case-insensitive because both arguments are all in one case. Simple and lite.

Answer 2

This version of my previous answer works in both D2007 and D2010.

• In Delphi 2007 the CharUpCaseTable is 256 bytes
• In Delphi 2010 it is 128 KB (65535*2).

The reason is Char size. In the older version of Delphi my original code only supported the current locale character set at initialization. My InsensPosEx is about 4 times faster than your code. Certainly it is possible to go even faster, but we would lose simplicity.

type
  TCharUpCaseTable = array [Char] of Char;

var
  CharUpCaseTable: TCharUpCaseTable;

procedure InitCharUpCaseTable(var Table: TCharUpCaseTable);
var
  n: cardinal;
begin
  for n := 0 to Length(Table) - 1 do
    Table[Char(n)] := Char(n);
  CharUpperBuff(@Table, Length(Table));
end;

function InsensPosEx(const SubStr, S: string; Offset: Integer = 1): Integer;
var
  n:            Integer;
  SubStrLength: Integer;
  SLength:      Integer;
label
  Fail;
begin
  Result := 0;
  if S = '' then Exit;
  if Offset <= 0 then Exit;

  SubStrLength := Length(SubStr);
  SLength := Length(s);

  if SubStrLength > SLength then Exit;

  Result := Offset;
  while SubStrLength <= (SLength-Result+1) do 
  begin
    for n := 1 to SubStrLength do
      if CharUpCaseTable[SubStr[n]] <> CharUpCaseTable[s[Result+n-1]] then
        goto Fail;
      Exit;
Fail:
    Inc(Result);
  end;
  Result := 0;
end;

//...

initialization
  InitCharUpCaseTable({var}CharUpCaseTable);