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/** @file include/row0ext.ic
 Caching of externally stored column prefixes

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

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

/** Looks up a column prefix of an externally stored column.
 @return column prefix, or NULL if the column is not stored externally,
 or pointer to field_ref_zero if the BLOB pointer is unset */
UNIV_INLINE
const byte *row_ext_lookup_ith(
    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 ext->max_len */
{
  ut_ad(ext);
  ut_ad(len);
  ut_ad(i < ext->n_ext);

  *len = ext->len[i];

  ut_ad(*len <= ext->max_len);
  ut_ad(ext->max_len > 0);

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

/** Looks up a column prefix of an externally stored column.
 @return column prefix, or NULL if the column is not stored externally,
 or pointer to field_ref_zero if the BLOB pointer is unset */
UNIV_INLINE
const byte *row_ext_lookup(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 ext->max_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);
}