Wrap around data cell [GH-1]

lib/brain_love/vm.rb

@@ -66,8 +66,10 @@ def execute
         when DEC_DP
           @dp -= 1
         when INC_BYTE
+          @data[@dp] = 0 if @data[@dp] == 255
           @data[@dp] += 1
         when DEC_BYTE
+          @data[@dp] = 256 if @data[@dp] == 0
           @data[@dp] -= 1
         when PUTC
           @output.putc(@data[@dp].chr)

spec/brain_love/vm_spec.rb

@@ -40,6 +40,12 @@
     it "increments the byte at the pointer by one" do
       expect { vm.execute }.to change { vm.data[1] }.by(1)
     end
+
+    it "wraps around value" do
+      code = Array.new(256, BrainLove::VM::INC_BYTE).map(&:chr).join
+      vm = BrainLove::VM.new(code, input, output)
+      expect { vm.execute }.to change { vm.data[0] }.by(1)
+    end
   end
 
   describe "DEC_BYTE" do
@@ -48,6 +54,12 @@
     it "decrements the byte at the pointer by one" do
       expect { vm.execute }.to change { vm.data[1] }.by(1)
     end
+
+    it "wraps around value" do
+      code = BrainLove::VM::DEC_BYTE.chr
+      vm = BrainLove::VM.new(code, input, output)
+      expect { vm.execute }.to change { vm.data[0] }.by(255)
+    end
   end
 
   describe "PUTC" do