Author: Daniel Wischnewski

The Pos funciton of Delphi returns the first occurence of a sub string within a 
string, only. How to get the positions of the next occurences?

Answer:

Solve 1:

This solution was developed using Borland Delphi 5 Service Pack 1. It is based upon 
the Pos algorithm delivered by Borland within the Systems unit, completely written 
in Assembler. !!!It might work with other versions of Borland Delphi (3.x, 4.x, 
5.0) but has not been tested on them!!! 

The syntax is similar to the syntax of the Pos function supplied by Delphi: 

function NextPos(Substr: string; S: string; LastPos: DWORD = 0): DWORD;

NextPos returns the index value of the first character in a specified substring 
that occurs in a given string starting after the index value supplied by LastPos. 
LastPos may be omitted. 

Note: As LastPos you should pass the position of the last occurence, not last 
position + 1. Just for convinience. 

Here the commented Code: 

1   function NextPos(SubStr: AnsiString; Str: AnsiString; LastPos: DWORD
2     = 0): DWORD;
3   type
4     StrRec = packed record
5       allocSiz: Longint;
6       refCnt: Longint;
7       length: Longint;
8     end;
9   const
10    skew = sizeof(StrRec);
11  
12    asm
13    // Search-String passed?
14    TEST    EAX,EAX
15    JE      @@noWork
16  
17    // Sub-String passed?
18    TEST    EDX,EDX
19    JE      @@stringEmpty
20  
21     // Save registers affected
22  PUSH ECX
23  PUSH EBX
24  PUSH ESI
25  PUSH EDI
26  
27  // Load Sub-String pointer
28  MOV ESI, EAX
29  // Load Search-String pointer
30  MOV EDI, EDX
31  // Save Last Position in EBX
32  MOV EBX, ECX
33  // Get Search-String Length
34  MOV ECX, [EDI - skew].StrRec.length
35  // subtract Start Position
36  SUB ECX, EBX
37  // Save Start Position of Search String to return
38  PUSH EDI
39  // Adjust Start Position of Search String
40  ADD EDI, EBX
41  // Get Sub-String Length
42  MOV EDX, [ESI - skew].StrRec.length
43  // Adjust
44  DEC EDX
45  // Failed if Sub-String Length was zero
46  JS@@fail
47  // Pull first character of Sub-String for SCASB function
48  MOV AL, [ESI]
49  // Point to second character for CMPSB function
50  INC ESI
51  // Load character count to be scanned
52  SUB ECX, EDX
53  // Failed if Sub-String was equal or longer than Search-String
54  JLE@@fail
55  @@loop:
56  // Scan for first matching character
57  REPNE SCASB
58  // Failed, if none are matching
59  JNE@@fail
60  // Save counter
61  MOV EBX, ECX
62  PUSH ESI
63  PUSH EDI
64  // load Sub-String length
65  MOV ECX, EDX
66  // compare all bytes until one is not equal
67  REPE CMPSB
68  // restore counter
69  POP EDI
70  POP ESI
71  // all byte were equal, search is completed
72  JE@@found
73  // restore counter
74  MOV ECX, EBX
75  // continue search
76  JMP@@loop
77  @@fail:
78  // saved pointer is not needed
79  POP EDX
80  xor EAX, EAX
81  JMP@@exit
82  @@stringEmpty:
83  // return zero - no match
84  xor EAX, EAX
85  JMP@@noWork
86  @@found:
87  // restore pointer to start position of Search-String
88  POP EDX
89  // load position of match
90  MOV EAX, EDI
91  // difference between position and start in memory is
92  //   position of Sub
93  SUB EAX, EDX
94  @@exit:
95  // restore registers
96  POP EDI
97  POP ESI
98  POP EBX
99  POP ECX
100 @@noWork:
101 end;



Solve 2:

102 PosEx function: 
103 
104 function PosEx(SubStr: string; s: string; Index: DWord): DWord;
105 var
106   I: Integer;
107 begin
108   I := Pos(SubStr, Copy(s, Index, Length(s) - Index + 1));
109   if I <> 0 then
110     I := I + Index - 1;
111   Result := I;
112 end;


The prarameter Index is the position you want to begin to search substr in s.