Answer: Provided in the explanation section
Explanation:
Str_find PROTO, pTarget:PTR BYTE, pSource:PTR BYTE
.data
target BYTE "01ABAAAAAABABCC45ABC9012",0
source BYTE "AAABA",0
str1 BYTE "Source string found at position ",0
str2 BYTE " in Target string (counting from zero).",0Ah,0Ah,0Dh,0
str3 BYTE "Unable to find Source string in Target string.",0Ah,0Ah,0Dh,0
stop DWORD ?
lenTarget DWORD ?
lenSource DWORD ?
position DWORD ?
.code
main PROC
INVOKE Str_find,ADDR target, ADDR source
mov position,eax
jz wasfound ; ZF=1 indicates string found
mov edx,OFFSET str3 ; string not found
call WriteString
jmp quit
wasfound: ; display message
mov edx,OFFSET str1
call WriteString
mov eax,position ; write position value
call WriteDec
mov edx,OFFSET str2
call WriteString
quit:
exit
main ENDP
;--------------------------------------------------------
Str_find PROC, pTarget:PTR BYTE, ;PTR to Target string
pSource:PTR BYTE ;PTR to Source string
;
; Searches for the first matching occurrence of a source
; string inside a target string.
; Receives: pointer to the source string and a pointer
; to the target string.
; Returns: If a match is found, ZF=1 and EAX points to
; the offset of the match in the target string.
; IF ZF=0, no match was found.
;--------------------------------------------------------
INVOKE Str_length,pTarget ; get length of target
mov lenTarget,eax
INVOKE Str_length,pSource ; get length of source
mov lenSource,eax
mov edi,OFFSET target ; point to target
mov esi,OFFSET source ; point to source
; Compute place in target to stop search
mov eax,edi ; stop = (offset target)
add eax,lenTarget ; + (length of target)
sub eax,lenSource ; - (length of source)
inc eax ; + 1
mov stop,eax ; save the stopping position
; Compare source string to current target
cld
mov ecx,lenSource ; length of source string
L1:
pushad
repe cmpsb ; compare all bytes
popad
je found ; if found, exit now
inc edi ; move to next target position
cmp edi,stop ; has EDI reached stop position?
jae notfound ; yes: exit
jmp L1 ; not: continue loop
notfound: ; string not found
or eax,1 ; ZF=0 indicates failure
jmp done
found: ; string found
mov eax,edi ; compute position in target of find
sub eax,pTarget
cmp eax,eax ; ZF=1 indicates success
done:
ret
Str_find ENDP
END main
cheers i hoped this helped !!
