1 files changed, 57 insertions, 0 deletions
diff --git a/src/vcall.h b/src/vcall.h
new file mode 100644
index 0000000..c92f8db
--- /dev/null
+++ b/src/vcall.h
@@ -0,0 +1,57 @@
+/*
+ * Copyright © 2021 Michael Smith <mikesmiffy128@gmail.com>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef INC_VCALL_H
+#define INC_VCALL_H
+
+/*
+ * Convenient facilities for calling simple (single-table) virtual functions on
+ * possibly-opaque pointers to C++ objects.
+ */
+
+#ifdef _WIN32
+#if defined(__GNUC__) || defined(__clang__)
+#define VCALLCONV __thiscall
+#else
+// XXX: could support MSVC via __fastcall and dummy param, but is there a point?
+#error C __thiscall support requires Clang or GCC
+#endif
+#else
+#define VCALLCONV
+#endif
+
+#define DECL_VFUNC0(ret, name, idx) \
+	enum { _VTIDX_##name = (idx) }; \
+	typedef ret (*VCALLCONV _VFUNC_##name)(void *this);
+
+#define DECL_VFUNC(ret, name, idx, ...) \
+	enum { _VTIDX_##name = (idx) }; \
+	typedef ret (*VCALLCONV _VFUNC_##name)(void *this, __VA_ARGS__);
+
+// not bothering to provide a zero-argument version because the main use of
+// this is vararg functions, which error if __thiscall
+#define DECL_VFUNC_CDECL(ret, name, idx, ...) \
+	enum { _VTIDX_##name = (idx) }; \
+	typedef ret (*_VFUNC_##name)(void *this, __VA_ARGS__);
+
+#define VFUNC(x, name) ((*(_VFUNC_##name **)(x))[_VTIDX_##name])
+
+#define VCALL0(x, name) (VFUNC(x, name)(x))
+#define VCALL(x, name, ...) VFUNC(x, name)(x, __VA_ARGS__)
+
+#endif
+
+// vi: sw=4 ts=4 noet tw=80 cc=80