/*
 *	UCW Library -- A simple growing buffer
 *
 *	(c) 2004, Robert Spalek <robert@ucw.cz>
 *	(c) 2005, Martin Mares <mj@ucw.cz>
 *
 *	Define the following macros:
 *
 *	GBUF_TYPE	data type of records stored in the buffer
 *	GBUF_PREFIX(x)	add a name prefix to all global symbols
 *	GBUF_TRACE(msg...) log growing of buffer [optional]
 *
 *	This software may be freely distributed and used according to the terms
 *	of the GNU Lesser General Public License.
 */

/**
 * Type identifier of the buffer.
 * The macro is not available outside the header file,
 * but it is used in the definitions of functions.
 **/
#define	BUF_T	GBUF_PREFIX(t)

/**
 * The growing buffer.
 * `ptr` holds the memory and `len` is the current
 * length of available memory.
 **/
typedef struct BUF_T {
  size_t len;
  GBUF_TYPE *ptr;
} BUF_T;

/**
 * Initializes an empty growing buffer in @b.
 **/
static inline void GBUF_PREFIX(init)(BUF_T *b)
{
  b->ptr = NULL;
  b->len = 0;
}

/**
 * Frees all memory in the buffer and returns it
 * to an empty state.
 **/
static void UNUSED GBUF_PREFIX(done)(BUF_T *b)
{
  if (b->ptr)
    xfree(b->ptr);
  b->ptr = NULL;
  b->len = 0;
}

/**
 * Sets the length of the buffer @b to exactly @len.
 * Do not use for the growing (you can use this at the end,
 * when you know the exact size), it would be slow.
 *
 * Use <<fun__GENERIC_LINK_|GBUF_PREFIX|grow|,`GBUF_PREFIX(grow)()`>>
 * for growing.
 **/
static void UNUSED GBUF_PREFIX(set_size)(BUF_T *b, size_t len)
{
  b->len = len;
  b->ptr = xrealloc(b->ptr, len * sizeof(GBUF_TYPE));
#ifdef GBUF_TRACE
  GBUF_TRACE(STRINGIFY_EXPANDED(BUF_T) " growing to %zu items", len);
#endif
}

static void UNUSED GBUF_PREFIX(do_grow)(BUF_T *b, size_t len)
{
  if (len < 2*b->len)			// to ensure logarithmic cost
    len = 2*b->len;
  GBUF_PREFIX(set_size)(b, len);
}

/**
 * Sets the size of the buffer @b to at last @len.
 * It grows in exponential manner, to ensure the total cost
 * of reallocs is linear with the final size.
 *
 * You can tweak the final size (when you do not need to grow
 * any more) by
 * <<fun__GENERIC_LINK_|GBUF_PREFIX|set_size|,`GBUF_PREFIX(set_size)()`>>.
 **/
static inline GBUF_TYPE *GBUF_PREFIX(grow)(BUF_T *b, size_t len)
{
  if (unlikely(len > b->len))
    GBUF_PREFIX(do_grow)(b, len);
  return b->ptr;
}

#undef	GBUF_TYPE
#undef	GBUF_PREFIX
#undef  GBUF_TRACE
#undef	BUF_T