Added functions to read/write bits in bitmap metadata

include/libmalloc/bitmap_alloc.h

@@ -98,6 +98,33 @@ typedef struct bitmap_heap_descriptor_t
 
 } bitmap_heap_descriptor_t;
 
+/**
+ * @brief Reads the given bit from the metadata of the memory block at 
+ * `location`. 
+ * 
+ * `location` must have be a location previously returned by `reserve_region`, 
+ * and not have been subsequently freed. `bit` must be less than the 
+ * `block_bits` field in `heap`.
+ * 
+ * @returns nonzero if `bit` is set, 0 otherwise. If `bit` is not less than the
+ * `block_bits` field in `heap`, returns nonzero.
+ */
+unsigned long read_bit(bitmap_heap_descriptor_t *heap, unsigned long location,
+    unsigned long bit);
+
+/**
+ * @brief Writes to the given bit in the metadata of the memory block at 
+ * `location`. 
+ * 
+ * `location` must have be a location previously returned by `reserve_region`, 
+ * and not have been subsequently freed. `bit` must be less than the 
+ * `block_bits` field in `heap`.
+ * 
+ * @returns `value` if bit was written to, nonzero otherwise
+ */
+int write_bit(bitmap_heap_descriptor_t *heap, unsigned long location,
+    unsigned long bit, int value);
+
 /**
  * @brief Reserves a region of memory within the heap containing at least `size`
  * bytes.

src/bitmap_alloc.c

@@ -197,6 +197,15 @@ static inline void uncache(bitmap_heap_descriptor_t *heap, int index)
     }
 }
 
+/*
+ * Computes the bitmap index of the block at `location` and `height`.
+ */
+static inline int block_index(bitmap_heap_descriptor_t *heap,
+    unsigned long location, unsigned long height)
+{
+    return (location / (heap->block_size * ((unsigned long)1 << height))) + (1 << (heap->height - height));
+}
+
 /*
  * Marks the indicated block as unavailable, and marks its children as both
  * available. Stores the right-hand child in the cache, and returns the index
@@ -401,6 +410,50 @@ static void initialize_bitmap(bitmap_heap_descriptor_t *heap, const memory_map_t
     }
 }
 
+unsigned long read_bit(bitmap_heap_descriptor_t *heap, unsigned long location,
+    unsigned long bit)
+{
+    int index = block_index(heap, location, 0);
+    while(index && !test_bit(heap, index, BIT_USED))
+    {
+        index /= 2;
+    }
+
+    if(index)
+    {
+        return test_bit(heap, index, bit);
+    }
+    else
+    {
+        return 1;
+    }
+}
+
+int write_bit(bitmap_heap_descriptor_t *heap, unsigned long location,
+    unsigned long bit, int value)
+{
+    int index = block_index(heap, location, 0);
+    while(index && !test_bit(heap, index, BIT_USED))
+    {
+        index /= 2;
+    }
+
+    if(index && value)
+    {
+        set_bit(heap, index, bit);
+        return value;
+    }
+    else if(index)
+    {
+        clear_bit(heap, index, bit);
+        return value;
+    }
+    else
+    {
+        return 1;
+    }
+}
+
 unsigned long reserve_region(bitmap_heap_descriptor_t *heap, unsigned long size)
 {
     int height = llog2((size - 1) / heap->block_size + 1);
@@ -422,7 +475,7 @@ void free_region(bitmap_heap_descriptor_t *heap, unsigned long location, unsigne
 {
     location -= heap->offset;
     int height = llog2(size / heap->block_size);
-    int index = (location / (heap->block_size * ((unsigned long)1 << height))) + (1 << (heap->height - height));
+    int index = block_index(heap, location, height);
     while(!test_bit(heap, index, BIT_USED))
     {
         height++;