;Recursive Ackermann-Peter-Function in x86 nasm-assembly
;@AUTHOR: Alexander Schneider, Düsseldorf, Germany 
;Ackermann-Peter-Function:
;A(n,m) = m + 1 if n == 0
;A(n,m) = A(n-1, 1) if n > 0 && m == 0
;A(n,m) = A(n-1, A(n, m-1)) if n > 0 && m > 0
;
;ecx is return the register

%include "asm_io.inc"

segment .data

	prompt1 db "Bitte n (>=0) für die Ackermann-Berechnung eingeben: ",10,0
	prompt2 db "Bitte m (>=0) für die Ackermann-Berechnung eingeben: ",10,0
	prompt3 db "Das Ergebniss ist: ",0
	promptError db "n und m müssen beide >= 0 sein",10,0
	debug db "Debug-Message",10,0
	
segment .bss

segment .data
	global asm_main
asm_main:
	ENTER 0,0				;setup Routine
	PUSHA
	MOV eax, prompt1		;ask for n
	CALL print_string
	CALL read_int
	CMP eax, 0				;check n
	JL inputError
	MOV ebx, eax			;save n
	MOV eax, prompt2		;ask for m
	CALL print_string
	CALL read_int
	CMP eax, 0				;check m
	JL inputError
	MOV edx, eax			;save m
	MOV ecx, 0
	PUSH ebp
	PUSH edx				;push m
	PUSH ebx				;push n
	CALL ackermann
	POP ebx
	POP edx
	POP ebp
	JMP result

ackermann:
	MOV edx, [ebp+8]		;get m
	MOV ebx, [ebp+12]		;get n
	CMP ebx, 0
	JE firstcase
	CMP edx, 0
	JE secondcase
	;inner ackermann return for m
	DEC edx
	PUSH ebp
	PUSH edx
	PUSH ebx
	CALL ackermann
	POP ebx
	POP edx
	POP ebp
	DEC ebx
	PUSH ebp
	PUSH edx				;return from last call is m
	PUSH ebx
	CALL ackermann
	POP ebx
	POP edx
	POP ebp
	RET
	
firstcase:
	MOV eax, debug
	CALL print_string
	MOV ecx, edx
	INC ecx
	RET
	
secondcase:
	DEC ebx
	PUSH ebp
	PUSH 1					;push m
	PUSH ebx				;push n
	CALL ackermann
	POP ebx
	POP edx
	POP ebp
	RET
	
result:
	MOV eax, prompt3
	CALL print_string		;print result
	MOV eax, ecx
	CALL print_int
	CALL print_nl
	
end:
	POPA
	MOV eax, 0				;return Value for C-driver
	LEAVE
	RET

inputError:					;n or m was <0
	MOV eax, promptError
	CALL print_string
	JMP end