bpf_dsl: support Switch/Case expressions

sandbox/linux/bpf_dsl/bpf_dsl.cc

Index: sandbox/linux/bpf_dsl/bpf_dsl.cc
diff --git a/sandbox/linux/bpf_dsl/bpf_dsl.cc b/sandbox/linux/bpf_dsl/bpf_dsl.cc
index de0a1ae449ac0e37a89fb6c584717f88b324ed88..a004971bdd952cab9d66ee275fb61fd84e8810fa 100644
--- a/sandbox/linux/bpf_dsl/bpf_dsl.cc
+++ b/sandbox/linux/bpf_dsl/bpf_dsl.cc
@@ -90,6 +90,24 @@ class IfThenResultExprImpl : public internal::ResultExprImpl {
   DISALLOW_COPY_AND_ASSIGN(IfThenResultExprImpl);
 };
 
+class ConstBoolExprImpl : public internal::BoolExprImpl {
+ public:
+  ConstBoolExprImpl(bool value) : value_(value) {}
+
+  virtual ErrorCode Compile(SandboxBPF* sb,
+                            ErrorCode true_ec,
+                            ErrorCode false_ec) const OVERRIDE {
+    return value_ ? true_ec : false_ec;
+  }
+
+ private:
+  virtual ~ConstBoolExprImpl() {}
+
+  bool value_;
+
+  DISALLOW_COPY_AND_ASSIGN(ConstBoolExprImpl);
+};
+
 class PrimitiveBoolExprImpl : public internal::BoolExprImpl {
  public:
   PrimitiveBoolExprImpl(int argno,
@@ -214,6 +232,10 @@ ResultExpr Trap(Trap::TrapFnc trap_func, void* aux) {
   return ResultExpr(new const TrapResultExprImpl(trap_func, aux));
 }
 
+BoolExpr BoolConst(bool value) {
+  return BoolExpr(new const ConstBoolExprImpl(value));
+}
+
 BoolExpr operator!(const BoolExpr& cond) {
   return BoolExpr(new const NegateBoolExprImpl(cond));
 }