lib: Use const-ref in for loops instead of const-copy

This is potentially a performance issue, even though it doesn't have
a big impact in this context. Clang will warn about it, and this fixes
the compiler warning.

2 files changed, 3 insertions, 3 deletions

diff --git a/host/lib/usrp/dboard/db_tvrx.cpp b/host/lib/usrp/dboard/db_tvrx.cpp
index 02fed018c..c9a940d15 100644
--- a/host/lib/usrp/dboard/db_tvrx.cpp
+++ b/host/lib/usrp/dboard/db_tvrx.cpp
@@ -158,7 +158,7 @@ static const boost::array<double, 17> tvrx_gains_volts = {{0.8,
 static uhd::dict<std::string, gain_range_t> get_tvrx_gain_ranges(void)
 {
     double rfmax = 0.0, rfmin = FLT_MAX;
-    for (const std::string range : tvrx_rf_gains_db.keys()) {
+    for (const std::string& range : tvrx_rf_gains_db.keys()) {
         double my_max = tvrx_rf_gains_db[range].back(); // we're assuming it's monotonic
         double my_min =
             tvrx_rf_gains_db[range].front(); // if it's not this is wrong wrong wrong
diff --git a/host/lib/usrp/dboard/magnesium/magnesium_radio_control_init.cpp b/host/lib/usrp/dboard/magnesium/magnesium_radio_control_init.cpp
index 82da7ec75..98c370275 100644
--- a/host/lib/usrp/dboard/magnesium/magnesium_radio_control_init.cpp
+++ b/host/lib/usrp/dboard/magnesium/magnesium_radio_control_init.cpp
@@ -227,7 +227,7 @@ void magnesium_radio_control_impl::_init_frontend_subtree(
     // TX gains
     std::vector<std::string> tx_gain_names = get_tx_gain_names(chan_idx);
     tx_gain_names.push_back("all");
-    for (const auto gain_name : tx_gain_names) {
+    for (const auto& gain_name : tx_gain_names) {
         subtree->create<double>(tx_fe_path / "gains" / gain_name / "value")
             .set_coercer([this, chan_idx, gain_name](const double gain) {
                 return this->set_tx_gain(gain, gain_name, chan_idx);
@@ -256,7 +256,7 @@ void magnesium_radio_control_impl::_init_frontend_subtree(
     // RX gains
     std::vector<std::string> rx_gain_names = get_rx_gain_names(chan_idx);
     rx_gain_names.push_back("all");
-    for (const auto gain_name : rx_gain_names) {
+    for (const auto& gain_name : rx_gain_names) {
         subtree->create<double>(rx_fe_path / "gains" / gain_name / "value")
             .set_coercer([this, chan_idx, gain_name](const double gain) {
                 return this->set_rx_gain(gain, gain_name, chan_idx);