void (*d_tf_fct)(void *, void *); /* doc term frequency function */
void (*d_idf_fct)(void *, void *); /* doc idf function */
void (*d_norm_fct)(void *, void *); /* doc normalization function */
void (*d_tf_fct)(void *, void *); /* doc term frequency function */
void (*d_idf_fct)(void *, void *); /* doc idf function */
void (*d_norm_fct)(void *, void *); /* doc normalization function */