Some more info in demo main

freelist/Makefile

@@ -1,6 +1,8 @@
 CC = gcc
 CFLAGS = -Wall -O2
 
+CFLAGS += -DFREELIST_NOALIGN
+
 TARGET = main.elf
 SRC = main.c freelist.c
 

freelist/freelist.c

@@ -4,23 +4,11 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
-
-/* Fiddle these around according to your need. */
-#ifdef FREELIST_NOALIGN
-#define ALIGN(x) (x)
-#else // FREELIST_NOALIGN
-
-/* Align to nearest multiple of sizeof(void*) */
-static inline size_t align_up(size_t n) {
-    return (n + sizeof(void *) - 1) & ~(sizeof(void *) - 1);
-}
-
-#define ALIGN(x) (align_up(x))
-#endif // FREELIST_NOALIGN
+#include <string.h>
 
 /* Initialize the FreeList */
 int fl_init(FreeList *fl, uintptr_t start, uintptr_t end, size_t itemsize) {
-    size_t size = ALIGN(itemsize + sizeof(FreeListBlock));
+    size_t size = ALIGN(itemsize);
 
     if (!fl || end <= start)
         return EXIT_FAILURE;
@@ -52,7 +40,8 @@ void *fl_alloc(FreeList *fl) {
     fl->free = fl->free->next;
     fl->allocated++;
 
-    return ((void *)m) + sizeof(FreeListBlock);
+    memset((void *)m, 0, sizeof(FreeListBlock));
+    return ((void *)m);
 }
 
 /* Return some memory to the FreeList */
@@ -61,7 +50,7 @@ int fl_free(FreeList *fl, void *ptr) {
         return EXIT_FAILURE; /* We cant free memory we do not own */
     }
 
-    FreeListBlock *block = (FreeListBlock *)((uintptr_t)ptr - sizeof(FreeListBlock));
+    FreeListBlock *block = (FreeListBlock *)(uintptr_t)ptr;
 
     block->next = fl->free;
     fl->free = block;

freelist/freelist.h

@@ -5,6 +5,19 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+/* Fiddle these around according to your need. Delete or check makefile */
+#ifdef FREELIST_NOALIGN
+#define ALIGN(x) (x)
+#else // FREELIST_NOALIGN
+
+/* Align to nearest multiple of sizeof(void*) */
+static inline size_t align_up(size_t n) {
+    return (n + sizeof(void *) - 1) & ~(sizeof(void *) - 1);
+}
+
+#define ALIGN(x) (align_up(x))
+#endif // FREELIST_NOALIGN
+
 #define FL_FREE ((uint8_t)0x00)
 #define FL_USED ((uint8_t)0x01)
 

freelist/main.c

@@ -17,16 +17,21 @@ void printvec(const Vec3 *v) {
     printf("Vec3: (%d, %d, %d)\n", v->x, v->y, v->z);
 }
 
+#define BUFFER_SIZE (4096)
+
 int main() {
     FreeList    fl;
-    char    *mem = malloc(4096);
+    const char *mem = malloc(BUFFER_SIZE);
+
+    fl_init(&fl, (uintptr_t)mem, (uintptr_t)mem + BUFFER_SIZE, sizeof(Vec3));
+    const size_t cap = fl_capacity(&fl);
+
+    printf("Item size: %lu\n", sizeof(Vec3));
+    printf("Buffer size: %d\n", BUFFER_SIZE);
+    printf("Space utilization internal: %.2f%%\n", 100.0 * fl_utilization(&fl, sizeof(Vec3)));
 
-    fl_init(&fl, (uintptr_t)mem, (uintptr_t)mem + 4096, sizeof(Vec3));
-    size_t cap = fl_capacity(&fl);
     assert(fl_available(&fl) == cap);
 
-    printf("Space utilization: %.2f%%\n", 100.0 * fl_utilization(&fl, sizeof(Vec3)));
-
     Vec3 *a = fl_alloc(&fl);
     Vec3 *b = fl_alloc(&fl);
     Vec3 *c = fl_alloc(&fl);