Need a very fast case insensitive way of finding the last occurence of a WIDESTRING in another

unit1.dfm
==========
object Form1: TForm1
  Left = 192
  Top = 114
  Width = 544
  Height = 420
  Caption = 'Form1'
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
  object Label1: TLabel
    Left = 72
    Top = 208
    Width = 47
    Height = 13
    Caption = 'Sub string'
  end
  object Button1: TButton
    Left = 312
    Top = 248
    Width = 177
    Height = 41
    Caption = 'Last Occurence'
    TabOrder = 0
    OnClick = Button1Click
  end
  object Memo1: TMemo
    Left = 2
    Top = 1
    Width = 525
    Height = 188
    Lines.Strings = (
      'procedure TForm1.Button1Click(Sender: TObject);'
      ' var'
      '  A, B: WideString;'
      '  P: PWideChar;'
      ''
      'begin'
      '  A := Edit1.Text;'
      '  B := Memo1.Text;'
      '  P := WStrPos(PWideChar(B), PWideChar(A));'
      ''
      '  if P = nil then ShowMessage(''FAIL #1 - P is nil!'')'
      '  else showmessage(WideString(P));'
      'end;')
    ScrollBars = ssBoth
    TabOrder = 1
  end
  object Edit1: TEdit
    Left = 136
    Top = 200
    Width = 257
    Height = 21
    TabOrder = 2
    Text = 'showmessage'
  end
  object Button2: TButton
    Left = 48
    Top = 248
    Width = 201
    Height = 41
    Caption = 'First Occurence'
    TabOrder = 3
    OnClick = Button2Click
  end
  object Button3: TButton
    Left = 48
    Top = 312
    Width = 201
    Height = 41
    Caption = 'First Occurence(case insensitive)'
    TabOrder = 4
    OnClick = Button3Click
  end
  object Button4: TButton
    Left = 312
    Top = 312
    Width = 177
    Height = 41
    Caption = 'Last Occurence (case insensitive)'
    TabOrder = 5
    OnClick = Button4Click
  end
end
 
unit1.pas
==========
unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
 
type
  TForm1 = class(TForm)
    Button1: TButton;
    Memo1: TMemo;
    Edit1: TEdit;
    Label1: TLabel;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
function MyStrPosW(Str, SubStr: PWideChar): PWideChar;
asm
         PUSH EDI
         PUSH ESI
         PUSH EBX
         OR EAX, EAX
         JZ @@2
         OR EDX, EDX
         JZ @@2
         MOV EBX, EAX
         MOV EDI, EDX
         XOR AX, AX
         MOV ECX, 0FFFFFFFFH
         REPNE SCASW
         NOT ECX
         DEC ECX
         JZ @@2
         MOV ESI, ECX
         MOV EDI, EBX
         MOV ECX, 0FFFFFFFFH
         REPNE SCASW
         NOT ECX
         SUB ECX, ESI
         JBE @@2
         MOV EDI, EBX
         LEA EBX, [ESI - 1]
@@1:     MOV ESI, EDX
         LODSW
         REPNE SCASW
         JNE @@2
         MOV EAX, ECX
         PUSH EDI
         MOV ECX, EBX
         REPE CMPSW
         POP EDI
         MOV ECX, EAX
         JNE @@1
         LEA EAX, [EDI - 2]
         JMP @@3
 
@@2:     XOR EAX, EAX
@@3:     POP EBX
         POP ESI
         POP EDI
end;
 
 
function MyRStrPosW(Str, SubStr: PWideChar): PWideChar;
asm
        PUSH    EDI
        PUSH    ESI
        PUSH    EBX
        OR      EAX,EAX
        JE      @@2
        OR      EDX,EDX
        JE      @@2
        MOV     EBX,EAX
        MOV     EDI,EDX
        XOR     AX,AX
        MOV     ECX,0FFFFFFFFH
        REPNE   SCASW
        NOT     ECX
        DEC     ECX
        JZ      @@2
        MOV     ESI,ECX
        MOV     EDI,EBX
        MOV     ECX,0FFFFFFFFH
        REPNE   SCASW
        NOT     ECX
        SUB     ECX,ESI
        JBE     @@2
        LEA     EBX,[ESI-1]
@@1:    MOV     ESI,EDX
        MOV AX,[EDX]
        PUSH EBX
        LEA EDI,[EDI-4]
@@4:    MOV BX,[EDI]
        CMP AX,BX
        LEA EDI,[EDI-2]
        LOOPNE  @@4
        POP EBX
        JNE     @@2
        LEA EDI,[EDI+2]
        MOV     EAX,ECX
        PUSH    EDI
        MOV     ECX,EBX
        REPE    CMPSW
        POP     EDI
        MOV     ECX,EAX
        JNE     @@1
        LEA     EAX,[EDI]
        JMP     @@3
@@2:    XOR     EAX,EAX
@@3:    POP     EBX
        POP     ESI
        POP     EDI
end;
 
procedure TForm1.Button3Click(Sender: TObject);
 var
  A, B: WideString;
  P: PWideChar;
  x:Cardinal;
begin
  x:=GetTickCount;
  A := UpperCase(Edit1.Text);
  B := UpperCase(Memo1.Text);
  P := MyStrPosW(PWideChar(B), PWideChar(A));
  ShowMessage(IntToStr(GetTickCount-x));
  if P = nil then ShowMessage('FAIL #1 - P is nil!')
  else showmessage(WideString(P));
 
end;
 
 
 
procedure TForm1.Button1Click(Sender: TObject);
 var
  A, B: WideString;
  P: PWideChar;
  x:Cardinal;
begin
  x:=GetTickCount;
  A := Edit1.Text;
  B := Memo1.Text;
  P := MyRStrPosW(PWideChar(B), PWideChar(A));
  ShowMessage(IntToStr(GetTickCount-x));
  if P = nil then ShowMessage('FAIL #1 - P is nil!')
  else showmessage(WideString(P));
 
end;
 
procedure TForm1.Button2Click(Sender: TObject);
 var
  A, B: WideString;
  P: PWideChar;
  x:Cardinal;
begin
  x:=GetTickCount;
  A := Edit1.Text;
  B := Memo1.Text;
  P := MyStrPosW(PWideChar(B), PWideChar(A));
  ShowMessage(IntToStr(GetTickCount-x));
  if P = nil then ShowMessage('FAIL #1 - P is nil!')
  else showmessage(WideString(P));
 
end;
 
procedure TForm1.Button4Click(Sender: TObject);
 var
  A, B: WideString;
  P: PWideChar;
  x:Cardinal;
begin
  x:=GetTickCount;
  A := UpperCase(Edit1.Text);
  B := UpperCase(Memo1.Text);
  P := MyRStrPosW(PWideChar(B), PWideChar(A));
  ShowMessage(IntToStr(GetTickCount-x));
  if P = nil then ShowMessage('FAIL #1 - P is nil!')
  else showmessage(WideString(P));
end;
 
end.