June 2018 Update

Task/Loops-While/X86-Assembly/loops-while.x86

@@ -0,0 +1,40 @@
+; NASM 64 bit X86-64 assembly on Linux
+
+global main
+extern printf
+
+segment .data
+
+printffmt db `%ld\n`,0
+
+segment .text
+
+main:	
+    push rbp
+    mov rbp,rsp
+
+; used rbx and r12 because printf preserves these values
+
+    mov rbx,1024                 ; start with 1024
+    mov r12,2                    ; load 2 as divisor
+
+.toploop                         ; top of while loop
+    cmp rbx,0                    ; compare to 0
+    jle .done                    ; exit 0 or less
+
+    lea rdi,[printffmt]          ; print number in rsi
+    mov rsi,rbx                  ; mov to rsi as argument
+    call printf
+
+; calculate n/2 and save
+    xor rdx,rdx                  ; clear rdx for division
+    mov rax,rbx                  ; mov number to rax for division
+    idiv r12                     ; divide by 2
+    mov rbx,rax                  ; save n/2
+
+    jmp .toploop                 ; next loop
+
+.done
+    xor rax,rax                  ; return code 0
+    leave                        ; fix stack
+    ret                          ; return