/******************************************************
Caching of externally stored column prefixes

(c) 2006 Innobase Oy

Created September 2006 Marko Makela
*******************************************************/

#include "rem0types.h"

/************************************************************************
Looks up and caches a column prefix of an externally stored column. */

byte*
row_ext_lookup_low(
/*===============*/
				/* out: column prefix */
	row_ext_t*	ext,	/* in/out: column prefix cache */
	ulint		i,	/* in: index of ext->ext[] */
	const byte*	field,	/* in: locally stored part of the column */
	ulint		f_len,	/* in: length of field, in bytes */
	ulint*		len);	/* out: length of prefix, in bytes,
				at most REC_MAX_INDEX_COL_LEN */

/************************************************************************
Creates a cache of column prefixes of externally stored columns. */
UNIV_INLINE
row_ext_t*
row_ext_create(
/*===========*/
				/* out,own: column prefix cache */
	ulint		n_ext,	/* in: number of externally stored columns */
	const ulint*	ext,	/* in: col_no's of externally stored columns */
	ulint		zip_size,/* compressed page size, or 0 */
	mem_heap_t*	heap)	/* in: heap where created */
{
	row_ext_t*	ret = mem_heap_alloc(heap, (sizeof *ret)
					     + (n_ext - 1) * sizeof ret->len);

	ret->n_ext = n_ext;
	ret->ext = ext;
	ret->zip_size = zip_size;
	ret->buf = mem_heap_alloc(heap, n_ext * REC_MAX_INDEX_COL_LEN);
#ifdef UNIV_DEBUG
	memset(ret->buf, 0xaa, n_ext * REC_MAX_INDEX_COL_LEN);
#endif
	memset(ret->len, 0, n_ext * sizeof *ret->len);

	return(ret);
}

/************************************************************************
Looks up a column prefix of an externally stored column. */
UNIV_INLINE
byte*
row_ext_lookup(
/*===========*/
				/* out: column prefix, or NULL if
				the column is not stored externally */
	row_ext_t*	ext,	/* in/out: column prefix cache */
	ulint		col,	/* in: column number */
	const byte*	field,	/* in: locally stored part of the column */
	ulint		f_len,	/* in: length of field, in bytes */
	ulint*		len)	/* out: length of prefix, in bytes,
				at most REC_MAX_INDEX_COL_LEN */
{
	ulint	i;

	ut_ad(ext);
	ut_ad(field);
	ut_ad(len);

	for (i = 0; i < ext->n_ext; i++) {
		if (col == ext->ext[i]) {
			/* Return from the cache if found */
			if (ext->len[i]) {
				*len = ext->len[i];
				ut_ad(*len > f_len);
				return(ext->buf + i * REC_MAX_INDEX_COL_LEN);
			}

			/* Update the cache */
			return(row_ext_lookup_low(ext, i, field, f_len, len));
		}
	}

	return(NULL);
}