fix instruction positioning

use at as at and only compute difference when needed (to determine if
there is a jump in binary)
Easier to understand that way

test/arm/helper.rb

@@ -5,9 +5,16 @@ require_relative "../helper"
 # tests are named as per assembler code, ie test_mov testing mov instruction
 
 module Arm
+  class FakeBin
+    def byte_length
+      4
+    end
+  end
   module ArmHelper
     def setup
       @machine = Arm::ArmMachine
+      @binary = FakeBin.new
+      Risc::Position.set(@binary , 0)
     end
 
     # code is what the generator spits out, at least one instruction worth (.first)

test/arm/test_call.rb

@@ -19,8 +19,9 @@ module Arm
       Risc.machine.boot
       bin = Parfait::BinaryCode.new(1)
       Risc::Position.set(bin , 0x20)
+      Risc::Position.set(@binary , 0)
       code = @machine.call(	bin ,{} )#this jumps to the next instruction
-      Risc::Position.set(code , 0, 1)
+      Risc::Position.set(code , 0, @binary)
       assert_code code , :call, [0x09,0x0,0x0,0xeb]
     end
     def test_swi

test/arm/test_logic.rb

@@ -82,7 +82,7 @@ module Arm
     end
     def test_too_big_add
       code = @machine.add	 :r1 , :r1, 0x222
-      Risc::Position.set(code,0,1)
+      Risc::Position.set(code,0,@binary)
       # add 0x02 (first instruction) and then 0x220 shifted
       assert_code code , :add , [0x02,0x1c,0x91,0xe2] #e2 91 1e 02
       # added extra instruction to add "extra"
@@ -91,13 +91,13 @@ module Arm
 
     def label( pos = 0x22 + 8)
       l  = Risc.label("some" , "Label")
-      Risc::Position.set(l,pos , 1)
+      Risc::Position.set(l,pos , @binary)
       l
     end
 
     def test_move_object
       code = @machine.add( :r1 , label)
-      Risc::Position.set(code,0,0)
+      Risc::Position.set(code,0,@binary)
       assert_code code , :add , [0x22,0x10,0x9f,0xe2] #e2 9f 10 22
     end
 

test/arm/test_move.rb

@@ -22,7 +22,7 @@ module Arm
     end
     def test_mov_big
       code = @machine.mov  :r0,  0x222  # is not 8 bit and can't be rotated by the arm system in one instruction
-      Risc::Position.set(code,0,1)
+      Risc::Position.set(code,0,@binary)
       # mov 512(0x200) = e3 a0 0c 02    add 34(0x22) = e2 90 00 22
       assert_code code , :mov , [ 0x02,0x0c,0xb0,0xe3]
       assert_code code.next , :add , [ 0x22,0x00,0x90,0xe2]