From 8d7e4dfcb0104eae108f420daff68778c24f5164 Mon Sep 17 00:00:00 2001
From: Pedro de Oliveira <falsovsky@gmail.com>
Date: Thu, 14 Aug 2014 05:55:30 +0100
Subject: [PATCH] Document

---
 zx-brainfuck/main.asm | 48 ++++++++++++++++++++++---------------------
 1 file changed, 25 insertions(+), 23 deletions(-)

diff --git a/zx-brainfuck/main.asm b/zx-brainfuck/main.asm
index c642476..93ad9dd 100644
--- a/zx-brainfuck/main.asm
+++ b/zx-brainfuck/main.asm
@@ -61,38 +61,40 @@ end_main
 
 ; -------------------------------------
 
+; opcode comes in A
 loopup_table
-    pop de
-    ld de, lookup_tbl_opcodes
-    ld hl, lookup_tbl_routines
-    ld c, $9
+    pop de                  ; Remove return address from stack
+    ld de, lookup_tbl_opcodes ; Start of opcodes_tbl in DE
+    ld hl, lookup_tbl_routines ; Start of routines_tbl in HL
+    ld c, $9                ; Number of valid opcodes + 1
 loopup_table_loop
-    ld b, a
-    push bc
-    ld a, (de)
-    cp b
-    jr z, lookup_table_found
-    pop bc
-    ld a, b
-    inc de
+    ld b, a                 ; B = A (opcode to run)
+    push bc                 ; Push BC to the stack
+                            ; B = Opcode, C = counter
+    ld a, (de)              ; Read item from opcodes_tbl
+    cp b                    ; Is it the same?
+    jr z, lookup_table_found ; Found it!
+    pop bc                  ; Get values from stack
+    ld a, b                 ; A = B (opcode to run)
+    inc de                  ; Next item in opcodes_tbl
     inc hl
-    inc hl
-    dec c
-    jr z, lookup_table_default
-    jr loopup_table_loop
+    inc hl                  ; Next item in opcodes_routines              
+    dec c                   ; C = C -1
+    jr z, lookup_table_default ; Is it 0? Non valid opcode
+    jr loopup_table_loop    ; Repeat
 lookup_table_found
     pop bc
     jr lookup_table_ret
 lookup_table_default
-    ld de, continue
-    push de
-    ret
+    ld de, continue         ; DE = address to "continue" label
+    push de                 ; Send it to the stack
+    ret                     ; Return to last item in the stack
 lookup_table_ret
-    ld e, (hl)
-    inc hl
+    ld e, (hl)              ; Save the address of the routine to
+    inc hl                  ; be RETurned in DE
     ld d, (hl)
-    push de
-    ret
+    push de                 ; Send it to the stack
+    ret                     ; Return to last item in the stack
 
 ; -------------------------------------