;
;   Copyright (C) 2015, 2016, 2017, 2018 Marek Marecki
;
;   This file is part of Viua VM.
;
;   Viua VM is free software: you can redistribute it and/or modify
;   it under the terms of the GNU General Public License as published by
;   the Free Software Foundation, either version 3 of the License, or
;   (at your option) any later version.
;
;   Viua VM is distributed in the hope that it will be useful,
;   but WITHOUT ANY WARRANTY; without even the implied warranty of
;   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;   GNU General Public License for more details.
;
;   You should have received a copy of the GNU General Public License
;   along with Viua VM.  If not, see <http://www.gnu.org/licenses/>.
;

.function: factorial/2
    allocate_registers %5 local

    .name: 1 number
    .name: 2 result
    mul %result (move %result local %1 parameters) local (move %number local %0 parameters) local
    idec %number local

    ; if counter is equal to zero
    ; finish "factorial" calls
    if (eq %4 local %number local (integer %3 local 0) local) local finish

    frame ^[(copy %0 arguments %number local) (copy %1 arguments %result local)]
    call %result local factorial/2

    .mark: finish
    move %0 local %result local
    return
.end

.function: main/1
    allocate_registers %3 local

    .name: 1 number
    .name: 2 result
    ; store the number of which we want to calculate the factorial
    integer %number local 8
    ; store result (starts with 1)
    integer %result local 1

    ; create frame for two parameters:
    ; * first is a copy of the number
    ; * second is a reference to result register
    ;   because we want to display it here, after calls to factorial are finished
    frame ^[(copy %0 arguments %number local) (copy %1 arguments %result local)]
    call %result local factorial/2

    ; print result
    print %result local
    izero %0 local
    return
.end