;;; fibOverflowWord.asm
;;; D. Thiebaut
;;; computes fibonacci until overflow
;;; requires driver.c, asm_io.o, and asm_io.inc
;;;
;;; compile and link as follows:
;;;
;;; nasm -f elf -F stabs fibOverflow.asm
;;; gcc -o fibOverflow driver.c asm_io.o fibOverflow.o
;;;
%include "asm_io.inc"
%assign EXIT 1
;; -------------------------
;; data segment
;; -------------------------
section .data
msg1 db "fib(",0
msg2 db ") = ",0
section .bss
N equ 1000
fib resw N ; reserve 100 bytes
;; -------------------------
;; code area
;; -------------------------
section .text
global asm_main
;;; ---------------------------------------------------------
;;; main program
;;; ---------------------------------------------------------
asm_main:
;;; fib[0] = 1;
;;; fib[1] = 1;
;;; for ( i=2; i<100; i++ ) {
;;; temp = fib[i-1]+fib[i-2];
;;; if ( temp <= 0 ) break;
;;; fib[i] = temp;
;;; }
mov word[fib], 1
mov word[fib+2], 1
mov esi, 2*2 ; esi is 2*i
for: cmp esi, N*2
jge done
mov ax, word[fib+esi-2]
add ax, word[fib+esi-4]
cmp ax, 0
jle done
mov word[fib+esi], ax
call printFibi
add esi,2
jmp for
done: ret
;;; print "fib( %d ) = %d" % (i, fib(i) )
printFibi:
and eax, 0x0000ffff ; keep ax, clear the rest
push eax ; save fib(i) in stack
push esi ; save i in stack
mov eax, msg1
call print_string ; prints "fib( "
pop eax ; get esi in eax
shr eax, 1 ; because esi grows by 2 every time
call print_int ; print i
mov eax, msg2 ; print ") = "
call print_string
pop eax ; get fib(i) back from stack
call print_int ; print fact(i)
call print_nl ; next line
ret
