malloc: defined get_next_chunk, get_prev_chunk, and align

include/gc_alloc.h

@@ -1,19 +0,0 @@
-#ifndef GC_ALLOC_H
-#define GC_ALLOC_H
-
-#include <stdio.h>
-
-// Metadata for allocated memory
-struct gc_block_header {
-	size_t size;
-	int free;
-	struct gc_block_header *next;
-};
-
-// Performs allocations of SIZE bytes
-void *gc_malloc(size_t size);
-
-// Frees blocks of memory allocated by 'gc_alloc'
-void gc_free(void *ptr);
-
-#endif /* GC_ALLOC_H */

include/gc_malloc.h

@@ -0,0 +1,51 @@
+#ifndef GC_MALLOC_H
+#define GC_MALLOC_H
+
+#include <stdint.h>
+#include <unistd.h>
+
+// Generally, inline functions are preferable to macros resembling functions.
+// https://www.kernel.org/doc/html/v4.10/process/coding-style.html#data-structures
+
+#define OVERHEAD 1 /* Number of 8-byte segments for chunk size & flags */
+#define MAGIC 2 /* Number of 8-byte segments from top of chunk to fields */
+#define MIN 3 /* Minimum number of 8-byte segments for data in a chunk */
+
+/*
+ * Metadata and user data for allocated memory
+ *
+ * footer: user data for previous chunk
+ * size: size of chunk in bytes
+ * merge: flag to identify when the chunk can be coalesced
+ * free: flag to identify when the chunk is free
+ * next: pointer to next chunk in the free list
+ * prev: pointer to previous chunk in the free list
+ */
+struct gc_chunk {
+	uint64_t footer;
+	uint32_t size;
+	uint16_t merge;
+	uint16_t free;
+	struct gc_chunk *next;
+	struct gc_chunk *prev;
+};
+
+// Gets a pointer to the next chunk
+struct gc_chunk *get_next_chunk(struct gc_chunk *curr);
+
+// Gets a pointer to the previous chunk, ensuring that current can be coalesced
+struct gc_chunk *get_prev_chunk(struct gc_chunk *curr);
+
+// Updates chunk footer information
+void set_footer(struct gc_chunk *curr);
+
+// Gets footer information for the current chunk
+int get_footer(struct gc_chunk *curr);
+
+// Performs allocations of SIZE bytes
+void *gc_malloc(size_t size);
+
+// Frees blocks of memory allocated by 'gc_alloc'
+void gc_free(void *ptr);
+
+#endif /* GC_MALLOC_H */

src/gc_alloc.c

@@ -1,2 +0,0 @@
-#include "gc_alloc.h"
-

src/gc_malloc.c

@@ -0,0 +1,42 @@
+#include <assert.h>
+#include <stdint.h>
+#include <sys/mman.h>
+
+#include "gc_malloc.h"
+
+// Hides chunk header
+static inline void *hide(struct gc_chunk *curr)
+{
+	return (void *)((uint64_t *)curr + MAGIC);
+}
+
+// Reveals chunk header
+static inline struct gc_chunk *magic(void *mem)
+{
+	return (struct gc_chunk *)((uint64_t *)mem - MAGIC);
+}
+
+// Aligns the amount of memory requested by the user with chunk size
+static inline size_t align(size_t size)
+{
+	const size_t alignment = 8;
+	size = (size + (alignment - 1)) & ~(alignment - 1);
+
+	if (size <= MIN)
+		return MIN;
+	else
+		return size;
+}
+
+struct gc_chunk *get_next_chunk(struct gc_chunk *curr)
+{
+	unsigned size = curr->size;
+	return (struct gc_chunk *)((uint64_t *)curr + MAGIC + (size - 1));
+}
+
+struct gc_chunk *get_prev_chunk(struct gc_chunk *curr)
+{
+	assert(curr->merge);
+	unsigned size = curr->footer;
+	return (struct gc_chunk *)((uint64_t *)curr - (size - 1) - MAGIC);
+}