xor edi, edi      ; zero -longest chain            
 xor esi, esi      ; zero -inner loop counter       
 mov ecx, 1000000    ; set main loop counter        
 mov edx, ecx      ; copy to edx
begin:
 mov eax, edx      ; prepare for even/odd test
 and eax, 1       ; test even/odd number
 jz inner        ; if zero number is even
 lea eax, [edx*2+edx+1] ; number is odd perform 3n+1
 mov edx, eax      ; load result back to edx
inner:          
 shr edx, 1       ; numbers are all even now so div by 2
 inc esi        ; increment present number chain
 cmp edx, 1       ; if number is 1 we are done with it
 jne begin       ; continue chain
 cmp esi, edi      ; if chain > longest_chain
 jb outer        ; no, goto outer
 mov edi, esi      ; yes, update longest_chain
 mov ebx, ecx      ; save number having longest chain
outer:
 xor esi, esi      ; reset inner loop counter
 dec ecx        ; decrement outer loop counter
 mov edx, ecx      ; save as next number to iterate
 jnz begin       ; if outer loop counter > 0 continue
 mov eax, ebx      ; return final result