Mega Code Archive
How to Find a Substring in a String starting from any position in the String
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Title: How to Find a Substring in a String starting from any position in the String
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 }
{
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 {
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
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