/* ARM assembly Raspberry PI  */
/*  program nullobj.s   */

/* Constantes    */
.equ STDIN,  0                                        @ Linux input console
.equ STDOUT, 1                                        @ Linux output console
.equ EXIT,   1                                        @ Linux syscall
.equ READ,   3                                        @ Linux syscall
.equ WRITE,  4                                        @ Linux syscall

/* Initialized data */
.data
szCarriageReturn:       .asciz "\n"
szMessResult:           .asciz "Value is null.\n"     @ message result

iPtrObjet:		.int 0                        @ objet pointer

/* UnInitialized data */
.bss

/*  code section */
.text
.global main
main:                                                @ entry of program

    ldr r0,iAdriPtrObjet                             @ load pointer address
    ldr r0,[r0]                                      @ load pointer value
    cmp r0,#0                                        @ is null ?
    ldreq r0,iAdrszMessResult                        @ yes -> display message
    bleq affichageMess


100:                                                 @ standard end of the program
    mov r0, #0                                       @ return code
    pop {fp,lr}                                      @ restaur 2 registers
    mov r7, #EXIT                                    @ request to exit program
    svc 0                                            @ perform the system call

iAdrszMessResult:        .int szMessResult
iAdrszCarriageReturn:    .int szCarriageReturn
iAdriPtrObjet:           .int iPtrObjet
/******************************************************************/
/*     display text with size calculation                         */
/******************************************************************/
/* r0 contains the address of the message */
affichageMess:
    push {r0,r1,r2,r7,lr}                           @ save  registres
    mov r2,#0                                       @ counter length
1:                                                  @ loop length calculation
    ldrb r1,[r0,r2]                                 @ read octet start position + index
    cmp r1,#0                                       @ if 0 its over
    addne r2,r2,#1                                  @ else add 1 in the length
    bne 1b                                          @ and loop
                                                    @ so here r2 contains the length of the message
    mov r1,r0                                       @ address message in r1
    mov r0,#STDOUT                                  @ code to write to the standard output Linux
    mov r7, #WRITE                                  @ code call system "write"
    svc #0                                          @ call systeme
    pop {r0,r1,r2,r7,lr}                            @ restaur des  2 registres */
    bx lr                                           @ return