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; Int to  Ascii
;
; Converts integer in rax into a string saved at buffer pointed to by rdi.
; Works by repeatedly dividing by base to get each number backwards and converting each to ascii.
;
; @param rax Integer to convert
; @param ebx base
; @param rdi pointer to buffer to save string to
;
; @return void
;
; @todo find out how big the buffer is going to need to be based on the base requested
io_itoa:
    ;find out how big the buffer needs to be for biggest number
    ;TODO
    ;divide by base repeatedly to get each number
    mov     ecx,20             ;maximum size the string could be (in base 10), this needs to be calculated
    @@:
    xor     edx,edx            ;clear rdx - clearing edx clears top half of rdx too, inconsistent with rest of architecture :/
    div     rbx                ;divide by the requested base in ebx
    add     edx,'0'            ;add ascii number for 0
    mov     byte[rdi+rcx-1],dl ;put numbers at end of buffer -> start of buffer
    cmp     eax,0              ;stop when the quotient is 0, no more numbers to convert
    je      @F
    dec     ecx
    jnz     @B
    @@:
    ;shift number left
    xor     ebx,ebx
    @@:
    mov     al,byte[rdi+rcx-1] ;load last byte that was written into al
    mov     byte[rdi+rcx-1],' ';clear where it came from
    mov     [rdi+rbx],al       ;store start of buffer->end of buffer
    inc     ecx                ;goto next byte written to by previous routine
    inc     ebx                ;goto next byte from start
    cmp     ecx,21             ;needs to be one higher, not entirely sure why though.
    jne     @B
    ;null terminate
    mov     byte[rdi+rbx],0
    ret         

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10^x >= 2^64

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base^strlen < 2^64 

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; -----------------------------------------------------------------------------
; os_int_to_string -- Convert a binary interger into an string
;  IN:	RAX = binary integer
;	RDI = location to store string
; OUT:	RDI = points to end of string
;	All other registers preserved
; Min return value is 0 and max return value is 18446744073709551615 so your
; string needs to be able to store at least 21 characters (20 for the digits
; and 1 for the string terminator).
; Adapted from http://www.cs.usfca.edu/~cruse/cs210s09/rax2uint.s
os_int_to_string:
	push rdx
	push rcx
	push rbx
	push rax

	mov rbx, 10					; base of the decimal system
	xor ecx, ecx					; number of digits generated
os_int_to_string_next_divide:
	xor edx, edx					; RAX extended to (RDX,RAX)
	div rbx						; divide by the number-base
	push rdx					; save remainder on the stack
	inc rcx						; and count this remainder
	cmp rax, 0					; was the quotient zero?
	jne os_int_to_string_next_divide		; no, do another division

os_int_to_string_next_digit:
	pop rax						; else pop recent remainder
	add al, '0'					; and convert to a numeral
	stosb						; store to memory-buffer
	loop os_int_to_string_next_digit		; again for other remainders
	xor al, al
	stosb						; Store the null terminator at the end of the string

	pop rax
	pop rbx
	pop rcx
	pop rdx
	ret
; -----------------------------------------------------------------------------


; -----------------------------------------------------------------------------
; os_string_to_int -- Convert a string into a binary interger
;  IN:	RSI = location of string
; OUT:	RAX = integer value
;	All other registers preserved
; Adapted from http://www.cs.usfca.edu/~cruse/cs210s09/uint2rax.s
os_string_to_int:
	push rsi
	push rdx
	push rcx
	push rbx

	xor eax, eax			; initialize accumulator
	mov rbx, 10			; decimal-system's radix
os_string_to_int_next_digit:
	mov cl, [rsi]			; fetch next character
	cmp cl, '0'			; char preceeds '0'?
	jb os_string_to_int_invalid	; yes, not a numeral
	cmp cl, '9'			; char follows '9'?
	ja os_string_to_int_invalid	; yes, not a numeral
	mul rbx				; ten times prior sum
	and rcx, 0x0F			; convert char to int
	add rax, rcx			; add to prior total
	inc rsi				; advance source index
	jmp os_string_to_int_next_digit	; and check another char
	
os_string_to_int_invalid:
	pop rbx
	pop rcx
	pop rdx
	pop rsi
	ret
; -----------------------------------------------------------------------------