buflib: Change buflib_available() and add buflib_allocatable().

buflib_allocatable() is what buflib_available() was before (it was in fact
simply renamed). It returns the largest contiguous block of memory. This
can be allocated and will definitely succeed, although larger allocations
may also succeed if the buffer can be compacted and shrinked.

buflib_available() now counts all free bytes, contiguous or not. This
better matches the description and how the caller use it.

Change-Id: I511e4eb5f4cf1821d957b3f4ef8a685ce40fe289
Reviewed-on: http://gerrit.rockbox.org/481
Reviewed-by: Thomas Martitz <kugel@rockbox.org>
Tested-by: Thomas Martitz <kugel@rockbox.org>

firmware/buflib.c

@@ -647,9 +647,9 @@ free_space_at_end(struct buflib_context* ctx)
         return 0;
 }
 
-/* Return the maximum allocatable memory in bytes */
+/* Return the maximum allocatable contiguous memory in bytes */
 size_t
-buflib_available(struct buflib_context* ctx)
+buflib_allocatable(struct buflib_context* ctx)
 {
     union buflib_data *this;
     size_t free_space = 0, max_free_space = 0;
@@ -687,6 +687,29 @@ buflib_available(struct buflib_context* ctx)
         return 0;
 }
 
+/* Return the amount of unallocated memory in bytes (even if not contiguous) */
+size_t
+buflib_available(struct buflib_context* ctx)
+{
+    union buflib_data *this;
+    size_t free_space = 0;
+
+    /* now look if there's free in holes */
+    for(this = find_first_free(ctx); this < ctx->alloc_end; this += abs(this->val))
+    {
+        if (this->val < 0)
+        {
+            free_space += -this->val;
+            continue;
+        }
+    }
+
+    free_space *= sizeof(union buflib_data); /* make it bytes */
+    free_space += free_space_at_end(ctx);
+
+    return free_space;
+}
+
 /*
  * Allocate all available (as returned by buflib_available()) memory and return
  * a handle to it

firmware/core_alloc.c

@@ -67,6 +67,11 @@ size_t core_available(void)
     return buflib_available(&core_ctx);
 }
 
+size_t core_allocatable(void)
+{
+    return buflib_allocatable(&core_ctx);
+}
+
 int core_free(int handle)
 {
     return buflib_free(&core_ctx, handle);

firmware/include/buflib.h

@@ -143,15 +143,20 @@ void buflib_init(struct buflib_context *context, void *buf, size_t size);
 
 
 /**
- * Returns how many bytes left the buflib has to satisfy allocations.
+ * Returns the amount of unallocated bytes. It does not mean this amount
+ * can be actually allocated because they might not be contiguous.
  *
- * This function does not yet consider possible compaction so there might
+ * Returns: The number of unallocated bytes in the memory pool.
- * be more space left. This may change in the future.
- *
- * Returns: The number of bytes left in the memory pool.
  */
 size_t buflib_available(struct buflib_context *ctx);
 
+/**
+ * Returns the biggest possible allocation that can be determined to succeed.
+ *
+ * Returns: The amount of bytes of the biggest unallocated, contiguous region.
+ */
+size_t buflib_allocatable(struct buflib_context *ctx);
+
 
 /**
  * Allocates memory from buflib's memory pool

firmware/include/core_alloc.h

@@ -16,6 +16,7 @@ int core_alloc_maximum(const char* name, size_t *size, struct buflib_callbacks *
 bool core_shrink(int handle, void* new_start, size_t new_size);
 int core_free(int handle);
 size_t core_available(void);
+size_t core_allocatable(void);
 
 /* DO NOT ADD wrappers for buflib_buffer_out/in. They do not call
  * the move callbacks and are therefore unsafe in the core */