DIV in NASM always return 1












0














There are my all code:



SYS_EXIT  equ 1
SYS_READ equ 3
SYS_WRITE equ 4
STDIN equ 0
STDOUT equ 1

section .data

msg1 db `xF0x9Fx98x8E`, " Enter the A: "
len1 equ $- msg1

msg2 db `xF0x9Fx98x89`, " Than the B: "
len2 equ $- msg2

msg3 db `xF0x9Fx8DxB0`, " A > B: A / B - 1 = "
len3 equ $- msg3

msg4 db `xF0x9Fx8DxAA`, " A = B: -25"
len4 equ $- msg4

msg5 db `xF0x9Fx8Dx95`, " A < B: (B^3 - 5) / A = "
len5 equ $- msg5


section .bss

a resb 32
b resb 32
x resb 32

section .text
global _start ;must be declared for using gcc

_start: ;tell linker entry point
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg1
mov edx, len1
int 0x80

mov eax, SYS_READ
mov ebx, STDIN
mov ecx, a
mov edx, 32
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, b
mov edx, 32
int 0x80

; Comparing
mov eax, [a]
sub eax, '0'
mov ecx, [b]
sub ecx, '0'

cmp eax, ecx
jg Ab ;A grate than b
je AB ;A and B are equal
jl aB ;a smoller than B

Ab:
cdq
idiv ecx
dec eax

add eax, '0'
mov [x], eax

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg3
mov edx, len3
int 0x80

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, x
mov edx, 32
int 0x80
jmp exit ;go to exit

AB:
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg4
mov edx, len4
int 0x80
jmp exit ;go to exit

aB:
mov eax, ecx
imul ecx
imul ecx
mov ebx, '5'
sub ebx, '0'
sub eax, ebx

mov ecx, [a]
sub ecx, '0'
idiv ecx

add eax, '0'
mov [x], eax

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg5
mov edx, len5
int 0x80

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, x
mov edx, 1
int 0x80

exit:

mov eax, SYS_EXIT
xor ebx, ebx
int 0x80


In 'a' and 'b' I put different number between 0 and 9 but this operation always return 1. I checked out EDX and noticed that processor subtracts ECX from EAX only one times. In EAX he write 1, and in EDX - remainder from subtraction EAX and ECX.



When I enter a = 9 and b = 4 : EAX after dividing = 1 and EDX = 5. If I enter a = 6 and b = 2 : EAX = 1, EDX = 4



What happened?










share|improve this question
























  • Where are the declarations of a and b?
    – Michael
    Nov 12 '18 at 12:51










  • So what are some example inputs and outputs? And how did you establish that eax always gets the value 1 after the division? I don't see any code that prints the value of eax.
    – Michael
    Nov 12 '18 at 13:20










  • Sorry there mast be don't EDX but EAX. But not the problem. It's I just test registers.
    – Богуслав Павлишинець
    Nov 12 '18 at 13:26










  • processor subtracts ECX from EAX - where?
    – Armali
    Nov 12 '18 at 14:29










  • When I call DIV he write in EDX remainder: EAX - ECX, and in EAX he write 1 (he 1 times subtracts ECX from EAX)
    – Богуслав Павлишинець
    Nov 12 '18 at 14:32
















0














There are my all code:



SYS_EXIT  equ 1
SYS_READ equ 3
SYS_WRITE equ 4
STDIN equ 0
STDOUT equ 1

section .data

msg1 db `xF0x9Fx98x8E`, " Enter the A: "
len1 equ $- msg1

msg2 db `xF0x9Fx98x89`, " Than the B: "
len2 equ $- msg2

msg3 db `xF0x9Fx8DxB0`, " A > B: A / B - 1 = "
len3 equ $- msg3

msg4 db `xF0x9Fx8DxAA`, " A = B: -25"
len4 equ $- msg4

msg5 db `xF0x9Fx8Dx95`, " A < B: (B^3 - 5) / A = "
len5 equ $- msg5


section .bss

a resb 32
b resb 32
x resb 32

section .text
global _start ;must be declared for using gcc

_start: ;tell linker entry point
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg1
mov edx, len1
int 0x80

mov eax, SYS_READ
mov ebx, STDIN
mov ecx, a
mov edx, 32
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, b
mov edx, 32
int 0x80

; Comparing
mov eax, [a]
sub eax, '0'
mov ecx, [b]
sub ecx, '0'

cmp eax, ecx
jg Ab ;A grate than b
je AB ;A and B are equal
jl aB ;a smoller than B

Ab:
cdq
idiv ecx
dec eax

add eax, '0'
mov [x], eax

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg3
mov edx, len3
int 0x80

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, x
mov edx, 32
int 0x80
jmp exit ;go to exit

AB:
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg4
mov edx, len4
int 0x80
jmp exit ;go to exit

aB:
mov eax, ecx
imul ecx
imul ecx
mov ebx, '5'
sub ebx, '0'
sub eax, ebx

mov ecx, [a]
sub ecx, '0'
idiv ecx

add eax, '0'
mov [x], eax

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg5
mov edx, len5
int 0x80

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, x
mov edx, 1
int 0x80

exit:

mov eax, SYS_EXIT
xor ebx, ebx
int 0x80


In 'a' and 'b' I put different number between 0 and 9 but this operation always return 1. I checked out EDX and noticed that processor subtracts ECX from EAX only one times. In EAX he write 1, and in EDX - remainder from subtraction EAX and ECX.



When I enter a = 9 and b = 4 : EAX after dividing = 1 and EDX = 5. If I enter a = 6 and b = 2 : EAX = 1, EDX = 4



What happened?










share|improve this question
























  • Where are the declarations of a and b?
    – Michael
    Nov 12 '18 at 12:51










  • So what are some example inputs and outputs? And how did you establish that eax always gets the value 1 after the division? I don't see any code that prints the value of eax.
    – Michael
    Nov 12 '18 at 13:20










  • Sorry there mast be don't EDX but EAX. But not the problem. It's I just test registers.
    – Богуслав Павлишинець
    Nov 12 '18 at 13:26










  • processor subtracts ECX from EAX - where?
    – Armali
    Nov 12 '18 at 14:29










  • When I call DIV he write in EDX remainder: EAX - ECX, and in EAX he write 1 (he 1 times subtracts ECX from EAX)
    – Богуслав Павлишинець
    Nov 12 '18 at 14:32














0












0








0







There are my all code:



SYS_EXIT  equ 1
SYS_READ equ 3
SYS_WRITE equ 4
STDIN equ 0
STDOUT equ 1

section .data

msg1 db `xF0x9Fx98x8E`, " Enter the A: "
len1 equ $- msg1

msg2 db `xF0x9Fx98x89`, " Than the B: "
len2 equ $- msg2

msg3 db `xF0x9Fx8DxB0`, " A > B: A / B - 1 = "
len3 equ $- msg3

msg4 db `xF0x9Fx8DxAA`, " A = B: -25"
len4 equ $- msg4

msg5 db `xF0x9Fx8Dx95`, " A < B: (B^3 - 5) / A = "
len5 equ $- msg5


section .bss

a resb 32
b resb 32
x resb 32

section .text
global _start ;must be declared for using gcc

_start: ;tell linker entry point
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg1
mov edx, len1
int 0x80

mov eax, SYS_READ
mov ebx, STDIN
mov ecx, a
mov edx, 32
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, b
mov edx, 32
int 0x80

; Comparing
mov eax, [a]
sub eax, '0'
mov ecx, [b]
sub ecx, '0'

cmp eax, ecx
jg Ab ;A grate than b
je AB ;A and B are equal
jl aB ;a smoller than B

Ab:
cdq
idiv ecx
dec eax

add eax, '0'
mov [x], eax

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg3
mov edx, len3
int 0x80

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, x
mov edx, 32
int 0x80
jmp exit ;go to exit

AB:
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg4
mov edx, len4
int 0x80
jmp exit ;go to exit

aB:
mov eax, ecx
imul ecx
imul ecx
mov ebx, '5'
sub ebx, '0'
sub eax, ebx

mov ecx, [a]
sub ecx, '0'
idiv ecx

add eax, '0'
mov [x], eax

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg5
mov edx, len5
int 0x80

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, x
mov edx, 1
int 0x80

exit:

mov eax, SYS_EXIT
xor ebx, ebx
int 0x80


In 'a' and 'b' I put different number between 0 and 9 but this operation always return 1. I checked out EDX and noticed that processor subtracts ECX from EAX only one times. In EAX he write 1, and in EDX - remainder from subtraction EAX and ECX.



When I enter a = 9 and b = 4 : EAX after dividing = 1 and EDX = 5. If I enter a = 6 and b = 2 : EAX = 1, EDX = 4



What happened?










share|improve this question















There are my all code:



SYS_EXIT  equ 1
SYS_READ equ 3
SYS_WRITE equ 4
STDIN equ 0
STDOUT equ 1

section .data

msg1 db `xF0x9Fx98x8E`, " Enter the A: "
len1 equ $- msg1

msg2 db `xF0x9Fx98x89`, " Than the B: "
len2 equ $- msg2

msg3 db `xF0x9Fx8DxB0`, " A > B: A / B - 1 = "
len3 equ $- msg3

msg4 db `xF0x9Fx8DxAA`, " A = B: -25"
len4 equ $- msg4

msg5 db `xF0x9Fx8Dx95`, " A < B: (B^3 - 5) / A = "
len5 equ $- msg5


section .bss

a resb 32
b resb 32
x resb 32

section .text
global _start ;must be declared for using gcc

_start: ;tell linker entry point
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg1
mov edx, len1
int 0x80

mov eax, SYS_READ
mov ebx, STDIN
mov ecx, a
mov edx, 32
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, b
mov edx, 32
int 0x80

; Comparing
mov eax, [a]
sub eax, '0'
mov ecx, [b]
sub ecx, '0'

cmp eax, ecx
jg Ab ;A grate than b
je AB ;A and B are equal
jl aB ;a smoller than B

Ab:
cdq
idiv ecx
dec eax

add eax, '0'
mov [x], eax

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg3
mov edx, len3
int 0x80

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, x
mov edx, 32
int 0x80
jmp exit ;go to exit

AB:
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg4
mov edx, len4
int 0x80
jmp exit ;go to exit

aB:
mov eax, ecx
imul ecx
imul ecx
mov ebx, '5'
sub ebx, '0'
sub eax, ebx

mov ecx, [a]
sub ecx, '0'
idiv ecx

add eax, '0'
mov [x], eax

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg5
mov edx, len5
int 0x80

mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, x
mov edx, 1
int 0x80

exit:

mov eax, SYS_EXIT
xor ebx, ebx
int 0x80


In 'a' and 'b' I put different number between 0 and 9 but this operation always return 1. I checked out EDX and noticed that processor subtracts ECX from EAX only one times. In EAX he write 1, and in EDX - remainder from subtraction EAX and ECX.



When I enter a = 9 and b = 4 : EAX after dividing = 1 and EDX = 5. If I enter a = 6 and b = 2 : EAX = 1, EDX = 4



What happened?







linux nasm






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 12 '18 at 14:56

























asked Nov 12 '18 at 12:31









Богуслав Павлишинець

34




34












  • Where are the declarations of a and b?
    – Michael
    Nov 12 '18 at 12:51










  • So what are some example inputs and outputs? And how did you establish that eax always gets the value 1 after the division? I don't see any code that prints the value of eax.
    – Michael
    Nov 12 '18 at 13:20










  • Sorry there mast be don't EDX but EAX. But not the problem. It's I just test registers.
    – Богуслав Павлишинець
    Nov 12 '18 at 13:26










  • processor subtracts ECX from EAX - where?
    – Armali
    Nov 12 '18 at 14:29










  • When I call DIV he write in EDX remainder: EAX - ECX, and in EAX he write 1 (he 1 times subtracts ECX from EAX)
    – Богуслав Павлишинець
    Nov 12 '18 at 14:32


















  • Where are the declarations of a and b?
    – Michael
    Nov 12 '18 at 12:51










  • So what are some example inputs and outputs? And how did you establish that eax always gets the value 1 after the division? I don't see any code that prints the value of eax.
    – Michael
    Nov 12 '18 at 13:20










  • Sorry there mast be don't EDX but EAX. But not the problem. It's I just test registers.
    – Богуслав Павлишинець
    Nov 12 '18 at 13:26










  • processor subtracts ECX from EAX - where?
    – Armali
    Nov 12 '18 at 14:29










  • When I call DIV he write in EDX remainder: EAX - ECX, and in EAX he write 1 (he 1 times subtracts ECX from EAX)
    – Богуслав Павлишинець
    Nov 12 '18 at 14:32
















Where are the declarations of a and b?
– Michael
Nov 12 '18 at 12:51




Where are the declarations of a and b?
– Michael
Nov 12 '18 at 12:51












So what are some example inputs and outputs? And how did you establish that eax always gets the value 1 after the division? I don't see any code that prints the value of eax.
– Michael
Nov 12 '18 at 13:20




So what are some example inputs and outputs? And how did you establish that eax always gets the value 1 after the division? I don't see any code that prints the value of eax.
– Michael
Nov 12 '18 at 13:20












Sorry there mast be don't EDX but EAX. But not the problem. It's I just test registers.
– Богуслав Павлишинець
Nov 12 '18 at 13:26




Sorry there mast be don't EDX but EAX. But not the problem. It's I just test registers.
– Богуслав Павлишинець
Nov 12 '18 at 13:26












processor subtracts ECX from EAX - where?
– Armali
Nov 12 '18 at 14:29




processor subtracts ECX from EAX - where?
– Armali
Nov 12 '18 at 14:29












When I call DIV he write in EDX remainder: EAX - ECX, and in EAX he write 1 (he 1 times subtracts ECX from EAX)
– Богуслав Павлишинець
Nov 12 '18 at 14:32




When I call DIV he write in EDX remainder: EAX - ECX, and in EAX he write 1 (he 1 times subtracts ECX from EAX)
– Богуслав Павлишинець
Nov 12 '18 at 14:32












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