I'm creating an assembly language program with NASM on Linux. I'm trying to do a weighted average of 4 numbers where the 4th number entered has double the weighting of the others. If I use the numbers 30, 40, 50, 60, I'm calculating the weighted average as (30+40+50+60+60)/5. My code is:
SYS_EXIT equ 1
SYS_READ equ 3
SYS_WRITE equ 4
STDIN equ 0
STDOUT equ 1
segment .data
msg1 db "Enter exam grade 1: ", 0xA,0xD
len1 equ $- msg1
msg2 db "Enter exam grade 2: ", 0xA,0xD
len2 equ $- msg2
msg3 db "Enter exam grade 3: ", 0xA,0xD
len3 equ $- msg3
msg4 db "Enter final exam grade (worth double: ", 0xA,0xD
len4 equ $- msg4
msg5 db "The sum is: "
len5 equ $- msg5
segment .bss
num1 resb 3
num2 resb 3
num3 resb 3
num4 resb 3
res resb 4
section .text
global main
main:
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg1
mov edx, len1
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num1
mov edx, 3
int 0x80
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg2
mov edx, len2
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num2
mov edx, 4
int 0x80
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg3
mov edx, len3
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num3
mov edx, 3
int 0x80
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg4
mov edx, len4
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num4
mov edx, 3
int 0x80
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg5
mov edx, len5
int 0x80
mov eax, [num1] ; move num1 to register eax
sub eax, '0' ; sub '0' to convert eax bl from ASCII to decimal
mov ebx, [num2] ; move num2 to register ebx
sub ebx, '0' ; sub '0' to convert ebx from ASCII to decimal
mov ecx, [num3] ; move num3 to register ecx
sub ecx, '0' ; sub '0' to convert ecx from ASCII to decimal
mov edx, [num4] ; move num4 to register edx
sub edx, '0' ; sub '0' to convert edx from ASCII to decimal
add eax, ebx ; add ebx to eax
add eax, ecx ; add ecx to eax
add eax, edx ; add edx to eax
add eax, edx ; add edx to eax again
mov bl, '5' ; sub '0' to convert bl from ASCII to decimal
sub bl, '0' ; make bl a decimal
div bl ; divide by bl
add eax, '0' ; add '0' to convert the sum from decimal to ASCII
mov [res], eax ; storing the sum in memory location res
; print the sum
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, res
mov edx, 3
int 0x80
exit:
mov eax, SYS_EXIT
xor ebx, ebx
int 0x80
I can produce this exception if I enter these numbers:
Enter exam grade 1:
30
Enter exam grade 2:
40
Enter exam grade 3:
50
Enter final exam grade (worth double:
60
The sum is: Floating point exception
What causes my program to display Floating Point Exception (SIGFPE) and how can I fix this?
