Convert string to int. x86 32 bit Assembler using Nasm

by

Each character is only a single byte, but you probably want to add it to a larger result. Might as well go for 32 bits… (can hobble your routine to 16 bits if you really want to)

mov edx, num3entered ; our string
atoi:
xor eax, eax ; zero a "result so far"
.top:
movzx ecx, byte [edx] ; get a character
inc edx ; ready for next one
cmp ecx, '0' ; valid?
jb .done
cmp ecx, '9'
ja .done
sub ecx, '0' ; "convert" character to number
imul eax, 10 ; multiply "result so far" by ten
add eax, ecx ; add in current digit
jmp .top ; until done
.done:
ret

That’s off the top of my head and may have errors, but “something like that”. It’ll stop at the end of a zero-terminated string, or a linefeed-terminated string… or any invalid character (which you may not want). Modify to suit.

More Related Contents:

  1. How do I print an integer in Assembly Level Programming without printf from the c library?
  2. NASM Assembly convert input to integer?
  3. How does $ work in NASM, exactly?
  4. Which 2’s complement integer operations can be used without zeroing high bits in the inputs, if only the low part of the result is wanted?
  5. NASM x86 16-bit addressing modes [duplicate]
  6. Basic use of immediates vs. square brackets in YASM/NASM x86 assembly
  7. How to load a single byte from address in assembly
  8. In NASM labels next to each other in memory are printing both strings instead of first one
  9. Why isn’t my root directory being loaded? (FAT12)
  10. MOV src, dest (or) MOV dest, src?
  11. problem in understanding mul & imul instructions of Assembly language
  12. x86, difference between BYTE and BYTE PTR
  13. What do the brackets mean in NASM syntax for x86 asm?
  14. Printing Hexadecimal Digits with Assembly [duplicate]
  15. Assembly difference between [var], and var
  16. Why do we need to disambiguate when adding an immediate value to a value at a memory address
  17. Near call/jump tables don’t always work in a bootloader
  18. NASM Error Parsing, Instruction Expected
  19. How to force NASM to encode [1 + rax*2] as disp32 + index*2 instead of disp8 + base + index?
  20. Second stage of bootloader prints garbage using Int 0x10/ah=0x0e
  21. Addressing Modes in Assembly Language (IA-32 NASM)
  22. Solution needed for building a static IDT and GDT at assemble/compile/link time
  23. Referencing the contents of a memory location. (x86 addressing modes)
  24. What do the E and R prefixes stand for in the names of Intel 32-bit and 64-bit registers?
  25. What is stack frame in assembly?
  26. How to push a 64bit int in NASM?
  27. gas: too many memory reference
  28. Add 2 numbers and print the result using Assembly x86
  29. Segment size in x86 real mode
  30. How is POPCNT implemented in hardware?

Leave a Comment