menambahkan program simple atoi #13
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slowy07
approved these changes
Jun 21, 2022
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terima kasih atas kontribusinya, bisakah kamu amend commit messagenya dengan mengawali messagenya sesuai dengan CONTRIBUTING.md?
ammarfaizi2
reviewed
Jul 28, 2022
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| mov al, byte 0 ;hasil perkalian | ||
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| section .data | ||
| num db 0 | ||
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num db 0 cuma allocate 1 byte saja, tapi di syscall readnya specify buffer
length 3 bytes. Overflow write to memory!!!
Kenapa tidak pakai uninitialized storage saja di .bss?
Misal:
section .bss
num resb 32
dan juga kenapa cuma 3 karakter doang readnya?
| _start: | ||
| ;code here | ||
| mov eax,3 ;sys_read | ||
| mov ebx,0 ;file desceiptor stdin |
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| mov eax,3 ;sys_read | ||
| mov ebx,0 ;file desceiptor stdin | ||
| mov ecx,num | ||
| mov edx,3 | ||
| int 0x80 |
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Read 3 bytes, kamu masukin angka 2 karakter, lalu enter itu sudah 3 bytes.
Gimana kalau inputnya lebih dari 2 karakter? Hmmm?
| ;hasil nya berada pada register eax tepatnya di al | ||
| end: | ||
| mov eax,1 | ||
| mov ebx,0 |
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| movzx edx, byte[edi] ;mov one byte edi to edx / dl | ||
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| cmp dl,48 ;jika kurang dari 0 end program | ||
| jl end | ||
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| cmp dl,57 ;jika lebih dari 9 end program | ||
| jg end | ||
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| mov bl,byte [edi] | ||
| sub bl, byte '0' | ||
| mov dl, byte 10 |
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| get_char: | ||
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| movzx edx, byte[edi] ;mov one byte edi to edx / dl | ||
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| cmp dl,48 ;jika kurang dari 0 end program | ||
| jl end | ||
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| cmp dl,57 ;jika lebih dari 9 end program | ||
| jg end | ||
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| mov bl,byte [edi] | ||
| sub bl, byte '0' | ||
| mov dl, byte 10 | ||
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| mul dl ;kali angka | ||
| add al,bl ;tambahkan hasil perkalian dengan digit input | ||
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| inc edi ;char selanjutnya | ||
| jmp get_char |
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This is very wrong atoi().
Simple test cases that prove this wrong:
+-------+-------+
| Input | Hasil |
+-------+-------+
| 3333 | 773 |
| 4444 | 1884 |
| 5555 | 435 |
+-------+-------+
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menambahkan program ataoi atau procedure c dengan versi simple