# Revision history [back]

### What is the usage of CV_DTREE_CAT_DIR?

What is the usage of CV_DTREE_CAT_DIR when categorical variables are used?

I do not understand the meaning of the micro defined below:

#define CV_DTREE_CAT_DIR(idx,subset) \
(2*((subset[(idx)>>5]&(1 << ((idx) & 31)))==0)-1)