Listing 1. Path element structure.

struct PathElement {

// Unique path index

size_t path_idx;

// Feature of this split, −1 is root

int64_t feature_idx;

// Range of feature value

float feature_lower_bound;

float feature_upper_bound;

// Probability of following this path

// when feature_idx is missing

float zero_fraction;

// Leaf weight at the end of path

float v;

};