Add slot allocator

.vscode/settings.json

@@ -1,14 +1,11 @@
 {
     "files.associations": {
-        "ringbuf.h": "c",
-        "seq.h": "c",
-        "stdint.h": "c",
-        "stdio.h": "c"
+        "*.h": "c",
     },
     "C_Cpp.default.includePath": [
         "/opt/homebrew/include/",
         "$(workspaceFolder)/include/",
 
-
-    ]
+    ],
+    "C_Cpp.default.cStandard": "gnu99"
 }

include/ucore/bitvec.h

@@ -27,7 +27,7 @@ struct UCBitVec {
  * Use as
  * @code
  * uc_bv_integer v[10];
- * struct UCBitVec v = BITVEC_STATIC_INIT(v);
+ * struct UCBitVec v = UC_BV_STATIC_INIT(v);
  * @endcode
  */
 #define UC_BV_STATIC_INIT(vec_data)\

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

src/bitvec.c

@@ -44,7 +44,7 @@ struct UCBitVec *uc_bv_new(size_t nbits)
 
 void uc_bv_free(struct UCBitVec *v)
 {
-    if (v) {
+    if (likely(v != NULL)) {
         free(v);
     }
 }

src/slot_allocator.c

@@ -0,0 +1,67 @@
+
+#include <stdio.h>
+#include <assert.h>
+#include <stdlib.h>
+#include "ucore/bitvec.h"
+#include "ucore/slot_allocator.h"
+
+void *uc_slot_alloc(UCSlotAlloc *sa)
+{
+    int free_slot = uc_bv_find_first_zero(&sa->bitmap);
+    if (free_slot < 0) {
+        return NULL;
+    } else if ((size_t)free_slot >= sa->num_slots) { // bit vector may have more bits than slots
+        return NULL;
+    }
+
+    uc_bv_set_bit(&sa->bitmap, free_slot);
+
+    return sa->slots + free_slot * sa->slot_size;
+}
+
+void uc_slot_free(UCSlotAlloc *restrict sa, void *restrict slot)
+{
+    assert((uint8_t *)slot >= sa->slots);
+    int slot_index = ((uint8_t *)slot - sa->slots) / sa->slot_size;
+    assert((size_t)slot_index < sa->num_slots);
+    uc_bv_clr_bit(&sa->bitmap, slot_index);
+}
+
+int main()
+{
+
+    UC_SLOT_ALLOC_DEF(sa, 24, 1)
+
+    void *p1 = uc_slot_alloc(&sa);
+    printf("%p\n", &sa_memory.memory[0]);
+    printf("%p\n", p1);
+
+    void *p2 = uc_slot_alloc(&sa);
+    printf("%p\n", p2);
+    uc_slot_free(&sa, p1);
+
+    p2 = uc_slot_alloc(&sa);
+    printf("%p\n", p2);
+
+    printf("__malloc__\n");
+    void *v = malloc(24 * (1<<16));
+    UC_SLOT_ALLOC_DEF_EX(sa2, 24, (1<<16), v)
+    char *v2 = NULL;
+    for (int i = 0; i < 1<<16; i++) {
+        char *c = uc_slot_alloc(&sa2);
+        if (c == NULL) {
+            printf("uc_slot_alloc failed at %d\n", i);
+            break;
+        }
+        *c = i;
+        if (i == 0) {
+            v2 = c;
+        }
+    }
+    for (int i = (1<<16) -1 ; i >= 0; i--) {
+        uc_slot_free(&sa2, v2 + 24*i);
+    }
+    free(v);
+    return 0;
+}
+