gitnik · April 10, 2013 20:56 · Apr 10, 2013
diff --git a/gistfile1.asm b/gistfile1.asm
@@ -0,0 +1,44 @@
+; ----------------------------------------------------------------------------
+; fib.asm
+;
+; This is a Win32 console program that writes the first 40 Fibonacci numbers.
+; It needs to be linked with a C library.
+; ----------------------------------------------------------------------------
+
+        global  _main
+        extern  _printf
+
+        section .text
+_main:
+        push    ebx                     ; we have to save this since we use it
+
+        mov     ecx, 40                 ; ecx will countdown from 40 to 0
+        xor     eax, eax                ; eax will hold the current number
+        xor     ebx, ebx                ; ebx will hold the next number
+        inc     ebx                     ; ebx is originally 1
+print:
+        ; We need to call printf, but we are using eax, ebx, and ecx.  printf
+        ; may destroy eax and ecx so we will save these before the call and
+        ; restore them afterwards.
+
+        push    eax
+        push    ecx
+
+        push    eax
+        push    format
+        call    _printf
+        add     esp, 8
+
+        pop     ecx
+        pop     eax
+
+        mov     edx, eax                ; save the current number
+        mov     eax, ebx                ; next number is now current
+        add     ebx, edx                ; get the new next number
+        dec     ecx                     ; count down
+        jnz     print                   ; if not done counting, do some more
+
+        pop     ebx                     ; restore ebx before returning
+        ret
+format:
+        db      '%d', 0x0a