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

(c) 2006 Innobase Oy

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

#include "rem0types.h"
#include "btr0types.h"

/************************************************************************
Looks up a column prefix of an externally stored column. */
UNIV_INLINE
const byte*
row_ext_lookup_ith(
/*===============*/
					/* out: column prefix, or NULL if
					the column is not stored externally,
					or pointer to field_ref_zero
					if the BLOB pointer is unset */
	const row_ext_t*	ext,	/* in/out: column prefix cache */
	ulint			i,	/* in: index of ext->ext[] */
	ulint*			len)	/* out: length of prefix, in bytes,
					at most REC_MAX_INDEX_COL_LEN */
{
	ut_ad(ext);
	ut_ad(len);
	ut_ad(i < ext->n_ext);

	*len = ext->len[i];

	if (UNIV_UNLIKELY(*len == 0)) {
		/* The BLOB could not be fetched to the cache. */
		return(field_ref_zero);
	} else {
		return(ext->buf + i * REC_MAX_INDEX_COL_LEN);
	}
}

/************************************************************************
Looks up a column prefix of an externally stored column. */
UNIV_INLINE
const byte*
row_ext_lookup(
/*===========*/
					/* out: column prefix, or NULL if
					the column is not stored externally,
					or pointer to field_ref_zero
					if the BLOB pointer is unset */
	const row_ext_t*	ext,	/* in: column prefix cache */
	ulint			col,	/* in: column number in the InnoDB
					table object, as reported by
					dict_col_get_no(); NOT relative to the
					records in the clustered index */
	ulint*			len)	/* out: length of prefix, in bytes,
					at most REC_MAX_INDEX_COL_LEN */
{
	ulint	i;

	ut_ad(ext);
	ut_ad(len);

	for (i = 0; i < ext->n_ext; i++) {
		if (col == ext->ext[i]) {
			return(row_ext_lookup_ith(ext, i, len));
		}
	}

	return(NULL);
}