stage0/Library function prototypes/clear_string.s

56 lines
1.4 KiB
ArmAsm

; This file is part of stage0.
;
; stage0 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.
;
; stage0 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 stage0. If not, see <http://www.gnu.org/licenses/>.
# We will be using R0 to pass pointer to string
# to cleared by the function
# R15 will be used as the stack pointer
:start
LOADUI R0 @string
LOADUI R1 22
LOADUI R2 33
LOADUI R3 44
LOADUI R4 55
LOADUI R15 0x600
CALLI R15 @clear_string
HALT
:string
HALT
HALT
NOP
;; Our simple string clear function
:clear_string
;; Preserve registers
PUSHR R0 R15
PUSHR R1 R15
PUSHR R2 R15
PUSHR R3 R15
;; Setup registers
MOVE R1 R0
LOADUI R2 0
LOADUI R3 0
:clear_byte
LOADXU8 R0 R1 R2 ; Get the byte
STOREX8 R3 R1 R2 ; Overwrite with a Zero
ADDUI R2 R2 1 ; Prep for next loop
JUMP.NZ R0 @clear_byte ; Stop if byte is NULL
;; Done
;; Restore registers
POPR R3 R15
POPR R2 R15
POPR R1 R15
POPR R0 R15
RET R15