rename register to risc

seems to fit the layer much better as we really have a very reduced
instruction set

lib/risc/instructions/branch.rb

@@ -0,0 +1,67 @@
+module Risc
+
+
+  # a branch must branch to a block.
+  class Branch < Instruction
+    def initialize source , to
+      super(source)
+      @label = to
+    end
+    attr_reader :label
+
+    def to_s
+      "#{self.class.name.split("::").last}: #{label ? label.name : ''}"
+    end
+    alias :inspect :to_s
+
+    def length labels = []
+      ret = super(labels)
+      ret += self.label.length(labels) if self.label
+      ret
+    end
+
+    def to_arr( labels = [] )
+      ret = super(labels)
+      ret += self.label.to_arr(labels) if self.label
+      ret
+    end
+
+    def total_byte_length labels = []
+      ret = super(labels)
+      ret += self.label.total_byte_length(labels) if self.label
+      #puts "#{self.class.name} return #{ret}"
+      ret
+    end
+
+    # labels have the same position as their next
+    def set_position position , labels = []
+      set_position self.label.set_position( position , labels ) if self.label
+      super(position,labels)
+    end
+
+    def assemble_all io , labels = []
+      self.assemble(io)
+      self.label.assemble_all(io,labels) if self.label
+      self.next.assemble_all(io, labels) if self.next
+    end
+
+    def each_label labels =[] , &block
+      super
+      self.label.each_label(labels , &block) if self.label
+    end
+
+  end
+
+  class IsZero < Branch
+  end
+
+  class IsNotzero < Branch
+  end
+
+  class IsMinus < Branch
+  end
+
+  class IsPlus < Branch
+  end
+
+end