DIV

hello,all



;========

mov edx, 41

mov eax,41

mov ebx,16

div ebx ; Integer overflow exception.

;=====



what's wrong?



regards

 

EDX:EAX divided by 16 is longer than 32 bits.

 

hey,AsmGuru62



Thanks you for help.

;==========

;41/16=?

mov edx, 41

xor eax,eax

mov ebx,16

div ebx

;==========

is it right?



regards

 

No.

Код (Text):

1. ;==========
2. ;41/16=?
3. mov eax, 41
4. xor edx,edx
5. mov ebx,16
6. div ebx
7. ;==========

 

Hey,tasman.

Thanks you.

it's ok.



regards.

 

if ebx=16 constant, next code is faster

Код (Text):

1.  
2. ;eax=eax/16
3. mov eax, 41
4. shr eax, 4
5.  

 

hey,yureckor



Thanks you for help.

;==========

;Local buffer1[128]:byte

;Local buffer2[128]:byte



mov esi, offset buffer1

mov edi, offset buffer2

invoke lstrlen, esi

shr eax,2

mov ecx,eax

.while ecx

lodsd

stosd

dec ecx

add esi,4

add edi,4

.endw

;==========



is it right?



regards

 

Код (Text):

1. ;Local buffer1[128]:byte
2. ;Local buffer2[128]:byte
3.     invoke lstrlen, addr buffer1
4.     lea esi, buffer1
5.     lea edi, buffer2
6.     mov edx, eax
7.     mov ecx, eax
8.     shr ecx,2
9.     rep movsd
10.     mov ecx, edx
11.     and ecx, 3
12.     rep movsb
13.  

Or use lstrcpy

Код (Text):

1. ;Local buffer1[128]:byte
2. ;Local buffer2[128]:byte
3.     invoke lstrcpy, addr buffer2, addr buffer1
4.  

 

Hey,SteelRat



Thanks you for help

This is the best method which I really need.



best wish to you.

 

dcskm4200

Your code is correct, but he slow, since 1) call Windows API, 2) The line can be copied during calculation of its length.

Код (Text):

1.  
2. ;return eax=lenght
3. copy_str proc src:DWORD, dst:DWORD
4. push esi
5. push edi
6. mov esi, [src]
7. mov edi, [dst]
8. xor eax, eax
9. @@1: mov al, [esi]
10.  mov [edi], al
11.  inc esi
12.  inc edi
13.  test eax, eax
14. jnz @@1
15. mov eax, esi
16. sub eax, [src]
17. pop edi
18. pop esi
19. ret
20. copy_str endp
21.  

Faster:

Код (Text):

1.  
2. ;return eax=lenght
3. copy_str_fast proc src:DWORD, dst:DWORD
4. push esi
5. push edi
6. mov esi, [src]
7. mov edi, [dst]
8. @@1: mov eax, [esi]
9.  mov [edi], eax
10.  test eax, 0000000FFh
11.  jz @@a1
12.  test eax, 00000FF00h
13.  jz @@a2
14.  test eax, 000FF0000h
15.  jz @@a3
16.  test eax, 0FF000000h
17.  jz @@a4
18.  add esi, 4
19.  add edi, 4
20. jmp @@1
21. @@a4: inc esi
22. @@a3: inc esi
23. @@a2: inc esi
24. @@a1:
25.  
26. mov eax, esi
27. sub eax, [src]
28.  
29. pop edi
30. pop esi
31. ret
32. copy_str_fast endp
33.  

You also can change function strlen.asm from MASM32\m32lib, but she works only with 7 bit letters that does not approach for Russian.

 

hey,yureckor



Thanks you for gave me more information.



we often need to encrypt or decrypt a buffer with a byte or word or dword. since you guided me, now I can manipulate it with a byte and dword. but i can't do it with a word.



regards