Create and use macros to define accessor functions

Avoids the need to manually mess around with mem_offset() and gamedata
off_ and sz_ values as often, because that's kind of annoying.

Should also make the codebase a little less confusing for new players.

1 files changed, 79 insertions, 0 deletions

diff --git a/src/accessor.h b/src/accessor.h
new file mode 100644
index 0000000..0da1209
--- /dev/null
+++ b/src/accessor.h
@@ -0,0 +1,79 @@
+/*
+ * Copyright © 2024 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_ACCESSOR_H
+#define INC_ACCESSOR_H
+
+#include "intdefs.h"
+#include "mem.h"
+
+#if defined(__GNUC__) || defined(__clang__)
+#define _ACCESSOR_UNUSED __attribute__((unused))
+#else
+#define _ACCESSOR_UNUSED
+#endif
+
+/*
+ * Defines a function to offset a pointer from a struct/class to a field based
+ * on a corresponding offset value off_<field>. Such an offset would be
+ * generally defined in gamedata. The function will be named getptr_<field>.
+ * Essentially allows easy access to an opaque thing contained with another
+ * opaque thing.
+ */
+#define DEF_PTR_ACCESSOR(type, field) \
+	_ACCESSOR_UNUSED static inline typeof(type) *getptr_##field(void *obj) { \
+		return mem_offset(obj, off_##field); \
+	}
+
+/*
+ * Does the same as DEF_PTR_ACCESSOR, and also adds direct get/get functions.
+ * Requires that the field type is complete - that is, either scalar or a fully
+ * defined struct.
+ */
+#define DEF_ACCESSORS(type, field) \
+	DEF_PTR_ACCESSOR(type, field) \
+	_ACCESSOR_UNUSED static inline typeof(type) get_##field(const void *obj) { \
+		return *getptr_##field((void *)obj); \
+	} \
+	_ACCESSOR_UNUSED static inline void set_##field(const void *obj, \
+			typeof(type) val) { \
+		*getptr_##field((void *)obj) = val; \
+	}
+
+/*
+ * Defines an array indexing function arrayidx_<class> which allows offsetting
+ * an opaque pointer by sz_<class> bytes. This size value would generally be
+ * defined in gamedata. Allows iterating over structs/classes with sizes that
+ * vary by game and are thus unknown at compile time.
+ *
+ * Note that idx is signed so this can also be used for relative pointer offsets
+ * in either direction.
+ *
+ * Note on performance: obviously doing n * size requires a multiplication by a
+ * global, which poses a bit of an optimisation challenge in loops. Based on
+ * some testing though it seems like this *should* usually be optimised into a
+ * single load of the global followed by repeated addition with no need for
+ * multiplication, given that we use LTO, so... don't worry about it! It's fine!
+ */
+#define DEF_ARRAYIDX_ACCESSOR(class) \
+	_ACCESSOR_UNUSED static inline struct class *arrayidx_##class(void *array, \
+			ssize idx) { \
+		return mem_offset(array, idx * sz_##class); \
+	}
+
+#endif
+
+// vi: sw=4 ts=4 noet tw=80 cc=80