format PE GUI 4.0 
entry Start 

include '%fasminc%\win32a.inc' 

section '.data' data readable writeable 
formatstr db '<1> %lu  <2> %lu  <3> %lu  <4> %lu',0 
searchstr db 'hello world 1 2 3',0 
findstr1 db 'ello',0 
findstr2 db ' 3',0 
findstr3 db '1 2',0 
findstr4 db 'zworld',0 
buffr rd 0ffh 

section '.code' code readable executable 
Start: 
push ebp 
mov ebp,esp 

push 6 
push dword findstr4 
push dword searchstr 
call InStr 
push eax ;save it 

push 3 
push dword findstr3 
push dword searchstr 
call InStr 
push eax 

push 2 
push findstr2 
push searchstr 
call InStr 
push eax 

push 2 
push findstr1 
push searchstr 
call InStr 
push eax 
;on stack 
;findstr1's result 
;...findstr4's result 
push formatstr 
push buffr 
call [wsprintf] 
push 0 
push buffr 
push buffr 
push 0 
call [MessageBox] 
mov esp,ebp 
pop ebp 
retn 0 

InStr: 
.MainStr equ ebp+8 ;main string ptr 
.Search equ ebp+12 ;search string ptr 
.LenSearch equ ebp+16 ;length of search string 
push ebp 
mov ebp,esp 
push esi 
push edi 
;the above just makes the procedure 
;just like the PROC macro would 
     mov edx,dword[.MainStr] 
     ;storing str address 
     dec edx 
     ;subtracting 1 from the address 
.LOOP: 
     add edx,1 
     ;adding 1 to the address 
     mov esi,edx 
     ;copy MainStr address into ESI 
     cmp byte[esi],0 
     ;check the string byte for null 
     je .NOMATCH 
     ;if its NULL we reached the end 
     ;of the search with NO results 
     ;so jump to the failure label 
     mov edi,dword[.Search] 
     ;copy address of the string to find 
     ;into EDI 
     mov ecx,dword[.LenSearch] 
     add ecx,1 
     ;copy length of string to find 
     ;into ECX and add 1 
     repe cmpsb 
     ;use slow string comparison opcode 
     ;dec ecx, cmp byte[esi],byte[edi], 
     ;inc esi,inc edi repeat it while equal 
     cmp ecx,0 
     ;if ecx = 0 success 
     jne .LOOP 
     ;if its not 0 loop again 
     mov eax,edx 
     ;put the offset address of where 
     ;the string was found into EAX 
     mov edx,dword[.MainStr] 
     ;put the address of the MainStr 
     ;into EDX 
     sub eax,edx 
     ;subtract offset from base to 
     ;get the index 
     ;first char = 0 2nd char = 1 etc. 
     jmp .END 
     ;skip the failure 
.NOMATCH: 
     mov eax,-1 
     ;couldnt find the string so 
     ;EAX = -1 failure 
.END: 
;the follow is like the EndProc macro 
pop edi 
pop esi 
mov esp,ebp 
pop ebp 
retn 0ch 

section '.idata' import data readable writeable 

  library kernel32,'KERNEL32.DLL',\ 
          user32,'USER32.DLL' 

      include  "%fasminc%\apia\kernel32.inc" 
      include  "%fasminc%\apia\user32.inc" 


section '.reloc' fixups data discardable 
    

proc InStr,Start,Search,Find

        enter
            push esi edi

                mov edx,[Search]
                dec edx
                add edx,[Start]        ; Set start position

            InStr_Do:

                inc edx
                mov esi,edx

                cmp byte [esi],0
                je InStr_Fail

                mov edi,[Find]
                invoke lstrlenA,[Find]
                mov ecx,eax

                inc ecx
                repe cmpsb

                cmp ecx,0
                jne InStr_Do

                mov eax,edx
                sub eax,[Search]
                inc eax                ; 1st char = 1; 2nd char = 2; ...

                jmp InStr_Exit

            InStr_Fail:

                mov eax,0              ; InStr returns 0 if not found

            InStr_Exit:

            pop edi esi
        return