Find-a-substring-in-a-string-starting-from-any-position-in-the-string


            //-----------------------------------------------------------------------------
// Name: cnsSmartPos
// Author: Com-N-Sense
// Date:
// Purpose: Find a substring in a string starting from any position in the string.
// Params: SubStr - a substring for search.
// S - the source string to search within
// StartPos - the index position to start the search.
// Result: Integer - the position of the substring,
// zero - if the substring was not found
// Remarks: This is the original Delphi "Pos" function modified to support
// the start pos parameter.
//-----------------------------------------------------------------------------
function SmartPosAsm(const substr : AnsiString; const s : AnsiString; StartPos : Cardinal) : Integer;
type
 StrRec = packed record
 allocSiz: Longint;
 refCnt: Longint;
 length: Longint;
 end;
const
 skew = sizeof(StrRec);
asm
{ ->EAX Pointer to substr }
{ EDX Pointer to string }
{ <-EAX Position of substr in s or 0 }
 TEST EAX,EAX
 JE @@noWork
 TEST EDX,EDX
 JE @@stringEmpty
 PUSH EBX
 PUSH ESI
 PUSH EDI
 MOV ESI,EAX { Point ESI to substr }
 MOV EDI,EDX { Point EDI to s }
 MOV EAX,ECX
 MOV ECX,[EDI-skew].StrRec.length { ECX = Length(s) }
 ADD EDI,EAX
 SUB ECX,EAX
 PUSH EDI { remember s position to calculate index }
 MOV EDX,[ESI-skew].StrRec.length { EDX = Length(substr) }
 DEC EDX { EDX = Length(substr) - 1 }
 JS @@fail { < 0 ? return 0 }
 MOV AL,[ESI] { AL = first char of substr }
 INC ESI { Point ESI to 2'nd char of substr }
 SUB ECX,EDX { #positions in s to look at }
 { = Length(s) - Length(substr) + 1 }
 JLE @@fail
@@loop:
 REPNE SCASB
 JNE @@fail
 MOV EBX,ECX { save outer loop counter }
 PUSH ESI { save outer loop substr pointer }
 PUSH EDI { save outer loop s pointer }
 MOV ECX,EDX
 REPE CMPSB
 POP EDI { restore outer loop s pointer }
 POP ESI { restore outer loop substr pointer }
 JE @@found
 MOV ECX,EBX { restore outer loop counter }
 JMP @@loop
@@fail:
 POP EDX { get rid of saved s pointer }
 XOR EAX,EAX
 JMP @@exit
@@stringEmpty:
 XOR EAX,EAX
 JMP @@noWork
@@found:
 POP EDX { restore pointer to first char of s }
 MOV EAX,EDI { EDI points of char after match }
 SUB EAX,EDX { the difference is the correct index }
@@exit:
 POP EDI
 POP ESI
 POP EBX
@@noWork:
end; //SmartPosAsm
function cnsSmartPos(const substr : AnsiString; const s : AnsiString; StartPos : Cardinal) : Integer;
begin
 dec(StartPos);
 Result := SmartPosAsm(SubStr,S,StartPos);
 if Result > 0 then Result := Result + StartPos;
end; //cnsSmartPos
Strings Delphi
