in src/annoylib.h [619:626]
static inline void normalize(Node* node, int f) {
T norm = sqrt(dot(node->v, node->v, f) + pow(node->dot_factor, 2));
if (norm > 0) {
for (int z = 0; z < f; z++)
node->v[z] /= norm;
node->dot_factor /= norm;
}
}