decoder: Generify the matcher interface (#33)

Gets rid of a bit of duplication while remaining compatible
with the current interfaces in place.

src/frontend/decoder/matcher.h

@@ -0,0 +1,78 @@
+/* This file is part of the dynarmic project.
+ * Copyright (c) 2016 MerryMage
+ * This software may be used and distributed according to the terms of the GNU
+ * General Public License version 2 or any later version.
+ */
+
+#pragma once
+
+#include <functional>
+
+#include "common/assert.h"
+
+namespace Dynarmic {
+namespace Arm {
+
+/**
+ * Generic instruction handling construct.
+ *
+ * @tparam Visitor An arbitrary visitor type that will be passed through
+ *                 to the function being handled. This type must be the
+ *                 type of the first parameter in a handler function.
+ *
+ * @tparam OpcodeType Type representing an opcode. This must be the
+ *                    type of the second parameter in a handler function.
+ */
+template <typename Visitor, typename OpcodeType>
+class Matcher {
+public:
+    using opcode_type         = OpcodeType;
+    using handler_return_type = typename Visitor::instruction_return_type;
+    using handler_function    = std::function<handler_return_type(Visitor&, opcode_type)>;
+
+    Matcher(const char* const name, opcode_type mask, opcode_type expected, handler_function func)
+        : name{name}, mask{mask}, expected{expected}, fn{std::move(func)} {}
+
+    /// Gets the name of this type of instruction.
+    const char* GetName() const {
+        return name;
+    }
+
+    /// Gets the mask for this instruction.
+    opcode_type GetMask() const {
+        return mask;
+    }
+
+    /// Gets the expected value after masking for this instruction.
+    opcode_type GetExpected() const {
+        return expected;
+    }
+
+    /**
+     * Tests to see if the given instruction is the instruction this matcher represents.
+     * @param instruction The instruction to test
+     * @returns true if the given instruction matches.
+     */
+    bool Matches(opcode_type instruction) const {
+        return (instruction & mask) == expected;
+    }
+
+    /**
+     * Calls the corresponding instruction handler on visitor for this type of instruction.
+     * @param v The visitor to use
+     * @param instruction The instruction to decode.
+     */
+    handler_return_type call(Visitor& v, opcode_type instruction) const {
+        ASSERT(Matches(instruction));
+        return fn(v, instruction);
+    }
+
+private:
+    const char* name;
+    opcode_type mask;
+    opcode_type expected;
+    handler_function fn;
+};
+
+} // namespace Arm
+} // namespace Dynarmic