more work

src/1_8.asm

@@ -1,7 +1,7 @@
     option casemap:none
 
 ; constants
-nl      =   10   ; newline
+nl      =   10  ; newline
 maxlen  =   256 ; max len of the string
 
     .data
@@ -17,10 +17,14 @@ input   byte    maxlen dup (?) ; make maxlen copies of byte, each uninitialized
     externdef printf:proc
     externdef readline:proc
 
+
+;; get_title procedure -------------------------
+;; get_title moves the address of the byte containing the string "Listing 1_8", 0
+;; into the RAX register, it does this usig the LEA instruction
     public get_title
 get_title proc
     
-    lea rax, title_string
+    lea rax, title_string   ; load address of title_string into rax
     ret 
 
 get_title endp
@@ -30,18 +34,21 @@ asm_main proc
 
     sub rsp, 56
 
-    ; first we want to print a prompt, to do this we use the C++ function printf
+    ;; first we want to print a prompt, to do this we use the stdio function printf, 
-    ; we load this prompt in RCX and then call
+    ;; we need to make the arguments for printf avaialble by loading the address of the
+    ;; byte prompt_string into RCX
     lea rcx, prompt_string
     call printf
 
-    mov input, 0
+    mov input, 0 ;; clear the input
 
-    ; read user input
+    ; read user input by calling readline from out cpp program. We load the required 
+    ; arguments into the registers RCX, and RDX and then call readline
     lea rcx, input
     mov rdx, maxlen
     call readline
 
+    ; load RCX and RDX with arugments to printf, to print back to the user
     lea rcx, format_string
     lea rdx, input
     call printf

src/c.cpp

@@ -8,6 +8,7 @@ extern "C"
 {
     void asm_main(void);
 
+    // function is defined in the asm file
     char *get_title(void);
 
     int readline(char* dest, int maxlen);

src/listing_1_9.cpp

@@ -0,0 +1 @@
+listing_1_9.cpp