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asm/5.md

@@ -0,0 +1,88 @@
+# Assembly x86_64 - Math operations 
+
+## Assembly Code 
+
+We're going to use vim to write our code
+    
+    
+    [ 192.168.0.18/24 ] [ /dev/pts/88 ] [~/binexp/asm]
+    → vim 5.asm
+    
+    
+    
+    
+    section .data
+            digit db 0, 10
+    
+    section .text
+            global _start
+    
+    
+    _start:
+            mov rbx, 48             ;48 in the ASCII chart is the "0" character
+            call _printRAX          ;print "0" + 1
+            call _printRAX          ;print "1" + 1
+            call _printRAX          ;print "2" + 1
+            call _printRAX          ;print "3" + 1
+            call _printRAX          ;print "4" + 1
+    
+            mov rax, 60
+            mov rdi, 0
+            syscall
+    
+    
+    
+    _printRAX:
+            add rbx, 1              ; we increment rbx by 1 (48, 49, 50, 51, ...)
+            mov [digit], rbx        ; we move the current value of rbx into the 'digit' memory address
+    
+            mov rax, 1              ; we use the syscall ID 1
+            mov rdi, 1              ; we set the first arg to 1
+            mov rsi, digit          ; the second arg is set to be our 'digit' memory address
+            mov rdx, 2              ; the third arg is the length of 2 bytes (let's not forget the newline char which is the '10' above)
+            syscall
+            ret
+    
+    
+    
+    
+
+Now let's check what's new in the code:
+    
+    
+       mov [digit], rbx    
+    
+    
+
+Here we are moving the rbx register into the memory address that's referenced by the 'digit' label.
+    
+    
+    	mov rbx, 48  
+            add rbx, 1          
+            mov [digit], rbx   
+    
+    
+
+Now first we set the value of rbx to be 48, which is the "0" character in ascii. Then we want to add the value 1 to the value stored in rbx. and then we just move the rbx value into the memory address referenced by the 'digit' label
+
+Basically our code should print the character 1, 2, 3, 4 and 5 
+
+## Compiling 
+
+Here we're going to use nasm to compile our assembly code: 
+    
+    
+    [ 192.168.0.18/24 ] [ /dev/pts/89 ] [~/binexp/asm]
+    → nasm -f elf64 5.asm -o 5.o
+    
+    [ 192.168.0.18/24 ] [ /dev/pts/89 ] [~/binexp/asm]
+    → ld 5.o -o 5
+    
+    [ 192.168.0.18/24 ] [ /dev/pts/89 ] [~/binexp/asm]
+    → ./5
+    12345%                                                               
+    
+    
+
+And that's it ! next tutorial we'll look into loops, you can click [here](6.html).
+