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I’m currently working on a simple webserver (http-daemon) entirely coded in FASM. It’s currently based on the Windows API and handles GET-requests only. In order to be able to compare requests with known commands I had to write a simple procedure handling string comparisons.

I commented each step of the code, therefore it shouldn’t be that hard to understand it:

[fasm]; Compares two strings and sets eax -> 1 if they’re equal
;
; Usage:
;   str_1 db ‘this is the first string’,0
;   str_2 db ‘this is the second string’,0
;
;   ccall CompareStrings, str1, str2
;   cmp eax, 1  ; address of string1

proc CompareStrings, str1, str2
lea edi, [str2] ; edi -> address of string2
dec edi          ; edi = edi – 1
.lab1:             ; loop through all chars and compare each of them
inc edi          ; ds:di –> next character in string2
lodsb            ; al = next char from string1. loadsb increments si automatically
cmp [edi], al    ; compare characters
jne .notfound    ; jump out of the loop if they’re unequal
cmp al, 0        ; chars are equal, but make sure we compared the entire string
jne .lab1        ; if not, continue the loop
mov eax, 1       ; else: strings are equal -> eax = 1
ret              ; return; result: strings are equal
.notfound:         ; chars are not equal
mov eax, 0       ; unequal -> eax = 0
ret              ; return; result: strings are not equal
endp[/fasm]

Comparing strings made easy.