use tagged pointers to optimize arrays

graphitemaster · Aug 20, 2023 · 5397033 · 5397033
1 parent 9eec6c8
commit 5397033
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Showing 3 changed files with 32 additions and 10 deletions.
diff --git a/src/array.c b/src/array.c
@@ -2,7 +2,7 @@
 #include "context.h"
 #include "allocator.h"
 
-Ptr array_create(Context *context) {
+static Ptr array_create_(Context *context) {
 	Allocator *allocator = &context->allocator;
 	Array *array = allocator_allocate(allocator, sizeof *array);
 	if (!array) {
@@ -16,6 +16,9 @@ Ptr array_create(Context *context) {
 
 void array_grow(void **const array, Size elements, Size type_size) {
 	ASSERT(*array);
+	if (!array_valid(*array)) {
+		*array = array_create_(tagptr_ptr(*array));
+	}
 	Array *meta = array_meta(*array);
 	Context *const context = meta->context;
 	Allocator *const allocator = &context->allocator;
@@ -33,7 +36,7 @@ void array_grow(void **const array, Size elements, Size type_size) {
 }
 
 void array_delete(void *const array) {
-	ASSERT(array);
+	if (!array) return;
 	Array *const meta = array_meta(array);
 	Context *const context = meta->context;
 	Allocator *const allocator = &context->allocator;

diff --git a/src/array.h b/src/array.h
@@ -16,21 +16,24 @@ struct ALIGN(16) Array {
 #define Array(T) T*
 
 #define array_make(context) \
-	array_create(context)
+	tagptr(context, 0x1)
+
+#define array_valid(array) \
+	(tagptr_tag(array) != 0x1)
 
 #define array_meta(array) \
 	(&RCAST(Array*, (array))[-1])
 
 #define array_try_grow(array, size_) \
-	(((array) && array_meta(array)->size + (size_) < array_meta(array)->capacity) \
+	((array_valid(array) && array_meta(array)->size + (size_) < array_meta(array)->capacity) \
 		? true \
 		: (array_grow(RCAST(void **, &(array)), (size_), sizeof *(array)), true))
 
 #define array_size(array) \
-	((array) ? array_meta(array)->size : 0)
+	(array_valid(array) ? array_meta(array)->size : 0)
 
 #define array_capacity(array) \
-	((arrray) ? array_meta(array)->capacity : 0)
+	(array_valid(array) ? array_meta(array)->capacity : 0)
 
 #define array_expand(array, size_) \
 	(array_try_grow((array), (size_)) \
@@ -50,10 +53,10 @@ struct ALIGN(16) Array {
 		: false)
 
 #define array_free(array) \
-	(void)((array) ? (array_delete(array), (array) = 0) : 0)
+	(void)(array_valid(array) ? (array_delete(array), (array) = 0) : 0)
 
 #define array_resize(array, size_) \
-	((array) \
+	(array_valid(array) \
 		? (array_meta(array)->size >= (size_) \
 			? (array_meta(array)->size = (size_), true) \
 			: array_expand((array), (size_) - array_meta(array)->size)) \
@@ -65,10 +68,9 @@ struct ALIGN(16) Array {
 	((array)[array_size(array) - 1])
 
 #define array_clear(array) \
-	(void)((array) ? array_meta(array)->size = 0 : 0)
+	(void)(array_valid(array) ? array_meta(array)->size = 0 : 0)
 
 void array_grow(void **const array, Size elements, Size type_size);
 void array_delete(void *const array);
-Ptr array_create(Context *context);
 
 #endif // CODIN_ARRAY_H
diff --git a/src/support.h b/src/support.h
@@ -152,8 +152,12 @@ struct Ptr {
 	constexpr operator bool() const noexcept { return p; }
 	void *p = 0;
 };
+#define PTR_TO_BITS(ptr) RCAST(Uint64, (ptr).p)
+#define PTR_FROM_BITS(bits) Ptr(RCAST(void *, (bits)))
 #else
 typedef void *Ptr;
+#define PTR_TO_BITS(ptr) RCAST(Uint64, ptr)
+#define PTR_FROM_BITS(bits) RCAST(Ptr, (bits))
 #endif
 
 // Support bitwise operators on enumerators in C++ like C.
@@ -188,6 +192,19 @@ constexpr T& operator^= (T& a, T b) noexcept {
 }
 #endif
 
+// Tagged pointer helpers assuming 16-byte aligned pointers
+static FORCE_INLINE Ptr tagptr(Ptr ptr, Uint8 tag) {
+	return PTR_FROM_BITS(PTR_TO_BITS(ptr) | tag);
+}
+
+static FORCE_INLINE Uint8 tagptr_tag(Ptr ptr) {
+	return PTR_TO_BITS(ptr) & 15;
+}
+
+static FORCE_INLINE Ptr tagptr_ptr(Ptr ptr) {
+	return PTR_FROM_BITS(PTR_TO_BITS(ptr) & ~15);
+}
+
 #if defined(__clang__) && defined(__cplusplus)
 #define THREAD_ATTRIBUTE(x) __attribute__((x))
 #else