Add slot allocator

include/ucore/slot_allocator.h

@@ -0,0 +1,112 @@
+#ifndef UC_SLOT_ALLOCATOR_H_
+#define UC_SLOT_ALLOCATOR_H_
+
+#include <stddef.h>
+#include <stdint.h>
+#include "ucore/bitvec.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+/** @file
+ * Fixed size slot memory allocator
+ *
+ * UCSlotAlloc is used to allocate fixed slots of memory from a pre-allocated
+ * piece of memory.
+ *
+ * The main use case is to keep allocated memory in a contiguous block for use
+ * maximum number of objects(slots) is known and relatively small. More than 131072 slots
+ * is not recommended.
+ *
+ * Note that this allocator is not thread safe.
+ *
+ * A bitmap is used to track which slots are allocated.
+ */
+
+
+
+typedef struct UCSlotAlloc UCSlotAlloc;
+struct UCSlotAlloc {
+    const uint32_t slot_size;
+    const uint32_t num_slots;
+    struct UCBitVec bitmap;
+    uint8_t *slots;
+};
+
+
+/** Initialize a UCSlotAlloc with an array as the backing memory to allocate slots from.
+ * The macro can be used at local scope to allocate memory automatic (stack) storage,
+ * or at global scope where the backin array will have static storage duration
+ *
+ * Use as:
+ * @code
+ * UC_SLOT_ALLOC_DEF(my_allocator, sizeof foo, 1024)
+ * struct foo *foo = uc_slot_alloc(&my_allocator);
+ * if (foo == NULL) {
+ *     // out of memory
+ * } else {
+ *     .. use foo
+ *     uc_slot_free(&my_allocator, foo);
+ * }
+ * @endcode
+ *
+ * @param var_name Variable name for the allocator
+ * @param v slot_size Memory size allocated for each slot
+ * @param v num_slots Number of slots to reserve memory for
+*/
+#define UC_SLOT_ALLOC_DEF(var_name, slot_size_, num_slots_) \
+struct {\
+    uc_bv_integer bitmap[UC_BV_LEN(num_slots_)]; \
+    uint8_t memory[num_slots_ * slot_size_] __attribute__((aligned)); \
+} var_name ## _memory = { \
+}; \
+UCSlotAlloc var_name = { \
+    .slot_size = slot_size_, \
+    .num_slots = num_slots_, \
+    .bitmap = UC_BV_STATIC_INIT(var_name ## _memory.bitmap), \
+    .slots = var_name ## _memory.memory \
+};
+
+/** Similar to UC_SLOT_ALLOC_DEF but allows you to specify the backing memory that must
+ * be atleast as large as num_slots * slot_size. Note that an array of num_slots * slot_size
+ * bits is also allocated for the bitmap with this definition
+ */
+#define UC_SLOT_ALLOC_DEF_EX(var_name, slot_size_, num_slots_, memory) \
+uc_bv_integer var_name ## _bitmap[UC_BV_LEN(num_slots_)] = {}; \
+UCSlotAlloc var_name = { \
+    .slot_size = slot_size_, \
+    .num_slots = num_slots_, \
+    .bitmap = UC_BV_STATIC_INIT(var_name ## _bitmap), \
+    .slots = memory \
+};
+
+/** Allocate a memory slot
+ *
+ * @param sa The allocator to allocate from
+ * @return A pointer to the memory slot that's sa.slot_size big, or NULL if
+ *          all slots are allocated
+ */
+void *uc_slot_alloc(UCSlotAlloc *sa);
+
+
+/** Free a memory slot previously returned from uc_slot_alloc()
+ *
+ * @param sa The allocator to free from.
+ * @param slot The memory slot to free. Passing a NULL pointer is undefined behavior
+ */
+void uc_slot_free(UCSlotAlloc *restrict sa, void *restrict slot);
+
+/** uc_slot_free() where the slot can be a  NULL pointer */
+#define uc_slot_free_safe(sa, slot) \
+do { \
+    if (slot != NULL) { \
+        uc_slot_free(sa, slot); \
+    } \
+} while (0)
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif