I have implemented an algorithm which converts a signed integer to its ASCII equivalent string with the corresponding sign as a first byte. I have tested it on several numbers and it worked correctly. But as a newbie I might have not noticed some logic mistakes or flaws.
I am asking for any ideas how to make this more efficient and elegant.
;;;;MACRO SECTION////////////////////////////////////////////////////////////// %macro Int2ascii 2 ;1 - number, 2 - string mov r12, %2 ;move ADDRESS of string mov eax, dword[%1] cmp eax, 0 jge %%placePlus ;check either number is negative or positive %%placeMinus: mov byte [r12], "-" ;fill the first (0th) byte with the sign mov rdi, -1 ;remember the sign ;neg eax ;negate number and forgot the sign (deprecated: see EDIT 1) jmp %%skipPlacePlus %%placePlus: mov byte [r12], "+" mov rdi, 1 ;remember the sign %%skipPlacePlus: xor rcx, rcx ;digit counter here (used implicitely in %%fillLoop) mov ebx, 10 %%divideLoop: cdq ;eax -> edx:eax idiv ebx ;signed division, reminder is also signed imul rdx, rdi ;"unsign" the current reminder ;div ebx ;(deprecated: see EDIT 1) push rdx ;push the reminder to stack inc rcx ;increment digit counter cmp eax, 0 jne %%divideLoop mov rdi, 1 ;note that the first (0th) byte was number sign (+/-) %%fillLoop: pop rax ;pop back reminders add al, "0" ;ascii code for digit mov byte [r12 + rdi], al ;fill string inc rdi loop %%fillLoop mov byte [r12 + rdi], 0x00 ;terminate string %endmacro
Example of output
As @TobySpeight suggested I have tested the above algorithm on numbers:
-1, 0, 1, 9, 10, 0x7fffffff, 0x80000000. Output is (
(gdb) x/s &sNegOne 0x600377: "-1" (gdb) x/s &sZero 0x600368: "+0" (gdb) x/s &sPosOne 0x600386: "+1" (gdb) x/s &sNine 0x600395: "+9" (gdb) x/s &sTen 0x6003a4: "+10" (gdb) x/s &sNumber1 0x6003b3: "+2147483647" (gdb) x/s &sNumber2 0x6003c2: "-2147483648"
I have realized that trying to consider only unsigned positive numbers leads to double-word overflow for initially valid double-word number
0x80000000 but invalid after taking absolute value
0x7fffffff + 1 which is no longer signed double-word number. I have overcome it by signed division. The problem here is for signed division reminders are also signed and no more applicable for storing as digits without additional processing which is just multiplying by -1 or 1 depending on sign.