void scalar_mul_and_add(
const common::sfv_t& left,
float s,
common::sfv_t& right) {
common::sfv_t::const_iterator l = left.begin();
common::sfv_t::iterator r = right.begin();
while (l != left.end() && r != right.end()) {
if (l->first < r->first) {
std::pair<std::string, float> p = *l;
p.second *= s;
r = right.insert(r, p);
++l;
} else if (l->first > r->first) {
++r;
} else {
r->second += l->second * s;
++l;
++r;
}
}
for (; l != left.end(); ++l) {
std::pair<std::string, float> p = *l;
p.second *= s;
right.push_back(p);
}
}
