implement offset addressing for load (ie reg+num)

lib/asm/arm/memory_access_builder.rb

@@ -28,32 +28,25 @@ module Asm
 
       # Build representation for target address
       def build_operand(arg)
-        #str / ldr are _seruous instructions. With BIG possibilities no half are implemented
+        #str / ldr are _serious instructions. With BIG possibilities not half are implemented
         @i = 0
         @pre_post_index = 0
         @w = 0
         @operand = 0
         if (arg.is_a?(Asm::RegisterNode))
           @rn = reg_ref(arg)
-  
-          if (false ) #argr.op and argr.right.is_a?(Asm::NumLiteralNode))
-  
-            # this if was buggy even before
-            # but as mentioned here we'd have to implement the options
-            # though a better syntax will have to be found
-            val = argr.right.value
-            if (val < 0)
+          if(arg.offset != 0) 
+            @operand = arg.offset
+            if (@operand < 0)
               @add_offset = 0
-              val *= -1
+              #TODO test/check/understand
+              @operand *= -1
             else
               @add_offset = 1
             end
-            if (val.abs > 4095)
+            if (@operand.abs > 4095)
               raise Asm::AssemblyError.new('reference offset too large/small (max 4095)', argr.right)
             end
-            @operand = val
-          else
-            # raise Asm::AssemblyError.new(Asm::ERRSTR_INVALID_ARG, arg)
           end
         elsif (arg.is_a?(Asm::LabelRefNode) or arg.is_a?(Asm::NumLiteralNode))
           @pre_post_index = 1

lib/asm/nodes.rb

@@ -11,10 +11,22 @@ module Asm
     attr_accessor :type, :value, :argument
   end
 
+  # Registers have off course a name (r1-16 for arm)
+  # but also refer to an address. In other words they can be an operand for instructions.
+  # Arm has addressing modes abound, and so can add to a register before actually using it
+  # If can actually shift or indeed shift what it adds, but not implemented
   class RegisterNode < Node
-    attr_accessor :name
+    attr_accessor :name , :offset
     def initialize name
       @name = name
+      @offset = 0 
+    end
+    
+    # this is for the dsl, so we can write pretty code like r1 + 4
+    # when we want to access the next word (4) after r1
+    def + number
+      @offset = number
+      self
     end
   end
 

test/test_crystal.rb

@@ -70,7 +70,7 @@ class TestArmAsm < MiniTest::Test
   end
   def test_ldr2
     code = @generator.instance_eval { ldr r0, r0 + 4 }.first
-    assert_code code, :ldr ,  [0x00,0x00,0x90,0xe5] #e5 90 00 00
+    assert_code code, :ldr ,  [0x04,0x00,0x90,0xe5] #e5 90 00 04
   end
   def test_ldrb
     code = @generator.instance_eval { ldrb r0, r0 }.first