uhd: Harmonize fuzzy frequency comparisons

Throughout UHD, we often do floating-point comparisons for frequency
ranges that require resilience to floating point rounding errors. Most
of the time the checks look like this:

```cpp
if (fp_compare_epsilon<double>(freq) > boundary) {
    // ...
}
```

The exception is the N320 daughterboard control, which uses a custom
epsilon:
```cpp
if (fp_compare_epsilon<double>(freq,
        RHODIUM_FREQ_COMPARE_EPSILON) > boundary) {
    // ...
}
```

This was, for the most part, not by design, but because authors simply
didn't think about which epsilon value was appropriate for the frequency
comparison. This was complicated by the fact that fp_compare_epsilon
previously had some issues.

This patch introduces FREQ_COMPARE_EPSILON, which is a sensible default
value for fp_compare_epsilon when doing frequency comparisons (note that
fp_compare_delta already had such a value).
Also, it introduces freq_compare_epsilon(x), which is a shorthand for
fp_compare_epsilon<double>(x, FREQ_COMPARE_EPSILON).

We then replace all occurrences of fp_compare_epsilon<double> which are
specific to frequency checks with freq_compare_epsilon.

7 files changed, 43 insertions, 43 deletions

diff --git a/host/lib/usrp/dboard/e3xx/e3xx_bands.cpp b/host/lib/usrp/dboard/e3xx/e3xx_bands.cpp
index e28acf3b9..e9226216b 100644
--- a/host/lib/usrp/dboard/e3xx/e3xx_bands.cpp
+++ b/host/lib/usrp/dboard/e3xx/e3xx_bands.cpp
@@ -146,21 +146,21 @@ e3xx_radio_control_impl::rx_band e3xx_radio_control_impl::map_freq_to_rx_band(
 {
     e3xx_radio_control_impl::rx_band band;
 
-    if (fp_compare_epsilon<double>(freq) < AD9361_RX_MIN_FREQ) {
+    if (freq_compare_epsilon(freq) < AD9361_RX_MIN_FREQ) {
         band = rx_band::INVALID_BAND;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_RX_LB_BAND3_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_RX_LB_BAND3_MIN_FREQ) {
         band = rx_band::LB_B2;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_RX_LB_BAND4_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_RX_LB_BAND4_MIN_FREQ) {
         band = rx_band::LB_B3;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_RX_LB_BAND5_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_RX_LB_BAND5_MIN_FREQ) {
         band = rx_band::LB_B4;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_RX_LB_BAND6_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_RX_LB_BAND6_MIN_FREQ) {
         band = rx_band::LB_B5;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_RX_LB_BAND7_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_RX_LB_BAND7_MIN_FREQ) {
         band = rx_band::LB_B6;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_RX_HB_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_RX_HB_MIN_FREQ) {
         band = rx_band::LB_B7;
-    } else if (fp_compare_epsilon<double>(freq) <= AD9361_RX_MAX_FREQ) {
+    } else if (freq_compare_epsilon(freq) <= AD9361_RX_MAX_FREQ) {
         band = rx_band::HB;
     } else {
         band = rx_band::INVALID_BAND;
@@ -174,25 +174,25 @@ e3xx_radio_control_impl::tx_band e3xx_radio_control_impl::map_freq_to_tx_band(
 {
     e3xx_radio_control_impl::tx_band band;
 
-    if (fp_compare_epsilon<double>(freq) < AD9361_TX_MIN_FREQ) {
+    if (freq_compare_epsilon(freq) < AD9361_TX_MIN_FREQ) {
         band = tx_band::INVALID_BAND;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_TX_LB_160_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_TX_LB_160_MIN_FREQ) {
         band = tx_band::LB_80;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_TX_LB_225_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_TX_LB_225_MIN_FREQ) {
         band = tx_band::LB_160;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_TX_LB_400_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_TX_LB_400_MIN_FREQ) {
         band = tx_band::LB_225;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_TX_LB_575_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_TX_LB_575_MIN_FREQ) {
         band = tx_band::LB_400;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_TX_LB_1000_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_TX_LB_1000_MIN_FREQ) {
         band = tx_band::LB_575;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_TX_LB_1700_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_TX_LB_1700_MIN_FREQ) {
         band = tx_band::LB_1000;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_TX_LB_2750_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_TX_LB_2750_MIN_FREQ) {
         band = tx_band::LB_1700;
-    } else if (fp_compare_epsilon<double>(freq) < E3XX_TX_HB_MIN_FREQ) {
+    } else if (freq_compare_epsilon(freq) < E3XX_TX_HB_MIN_FREQ) {
         band = tx_band::LB_2750;
-    } else if (fp_compare_epsilon<double>(freq) <= AD9361_TX_MAX_FREQ) {
+    } else if (freq_compare_epsilon(freq) <= AD9361_TX_MAX_FREQ) {
         band = tx_band::HB;
     } else {
         band = tx_band::INVALID_BAND;
diff --git a/host/lib/usrp/dboard/magnesium/magnesium_bands.cpp b/host/lib/usrp/dboard/magnesium/magnesium_bands.cpp
index ef72aee95..b54bf9a62 100644
--- a/host/lib/usrp/dboard/magnesium/magnesium_bands.cpp
+++ b/host/lib/usrp/dboard/magnesium/magnesium_bands.cpp
@@ -98,23 +98,23 @@ magnesium_radio_control_impl::rx_band magnesium_radio_control_impl::_map_freq_to
 {
     magnesium_radio_control_impl::rx_band band;
 
-    if (fp_compare_epsilon<double>(freq) < MAGNESIUM_MIN_FREQ) {
+    if (freq_compare_epsilon(freq) < MAGNESIUM_MIN_FREQ) {
         band = rx_band::INVALID_BAND;
-    } else if (fp_compare_epsilon<double>(freq) < MAGNESIUM_LOWBAND_FREQ) {
+    } else if (freq_compare_epsilon(freq) < MAGNESIUM_LOWBAND_FREQ) {
         band = rx_band::LOWBAND;
-    } else if (fp_compare_epsilon<double>(freq) < band_map.at(1)) {
+    } else if (freq_compare_epsilon(freq) < band_map.at(1)) {
         band = rx_band::BAND0;
-    } else if (fp_compare_epsilon<double>(freq) < band_map.at(2)) {
+    } else if (freq_compare_epsilon(freq) < band_map.at(2)) {
         band = rx_band::BAND1;
-    } else if (fp_compare_epsilon<double>(freq) < band_map.at(3)) {
+    } else if (freq_compare_epsilon(freq) < band_map.at(3)) {
         band = rx_band::BAND2;
-    } else if (fp_compare_epsilon<double>(freq) < band_map.at(4)) {
+    } else if (freq_compare_epsilon(freq) < band_map.at(4)) {
         band = rx_band::BAND3;
-    } else if (fp_compare_epsilon<double>(freq) < band_map.at(5)) {
+    } else if (freq_compare_epsilon(freq) < band_map.at(5)) {
         band = rx_band::BAND4;
-    } else if (fp_compare_epsilon<double>(freq) < band_map.at(6)) {
+    } else if (freq_compare_epsilon(freq) < band_map.at(6)) {
         band = rx_band::BAND5;
-    } else if (fp_compare_epsilon<double>(freq) <= MAGNESIUM_MAX_FREQ) {
+    } else if (freq_compare_epsilon(freq) <= MAGNESIUM_MAX_FREQ) {
         band = rx_band::BAND6;
     } else {
         band = rx_band::INVALID_BAND;
@@ -128,17 +128,17 @@ magnesium_radio_control_impl::tx_band magnesium_radio_control_impl::_map_freq_to
 {
     magnesium_radio_control_impl::tx_band band;
 
-    if (fp_compare_epsilon<double>(freq) < MAGNESIUM_MIN_FREQ) {
+    if (freq_compare_epsilon(freq) < MAGNESIUM_MIN_FREQ) {
         band = tx_band::INVALID_BAND;
-    } else if (fp_compare_epsilon<double>(freq) < MAGNESIUM_LOWBAND_FREQ) {
+    } else if (freq_compare_epsilon(freq) < MAGNESIUM_LOWBAND_FREQ) {
         band = tx_band::LOWBAND;
-    } else if (fp_compare_epsilon<double>(freq) < band_map.at(1)) {
+    } else if (freq_compare_epsilon(freq) < band_map.at(1)) {
         band = tx_band::BAND0;
-    } else if (fp_compare_epsilon<double>(freq) < band_map.at(2)) {
+    } else if (freq_compare_epsilon(freq) < band_map.at(2)) {
         band = tx_band::BAND1;
-    } else if (fp_compare_epsilon<double>(freq) < band_map.at(3)) {
+    } else if (freq_compare_epsilon(freq) < band_map.at(3)) {
         band = tx_band::BAND2;
-    } else if (fp_compare_epsilon<double>(freq) <= MAGNESIUM_MAX_FREQ) {
+    } else if (freq_compare_epsilon(freq) <= MAGNESIUM_MAX_FREQ) {
         band = tx_band::BAND3;
     } else {
         band = tx_band::INVALID_BAND;
diff --git a/host/lib/usrp/dboard/magnesium/magnesium_radio_control.cpp b/host/lib/usrp/dboard/magnesium/magnesium_radio_control.cpp
index 441e7b427..637d85d49 100644
--- a/host/lib/usrp/dboard/magnesium/magnesium_radio_control.cpp
+++ b/host/lib/usrp/dboard/magnesium/magnesium_radio_control.cpp
@@ -299,8 +299,8 @@ void magnesium_radio_control_impl::_update_freq(
                                              : ad9371_freq;
 
     RFNOC_LOG_TRACE("RF freq = " << rf_freq);
-    UHD_ASSERT_THROW(fp_compare_epsilon<double>(rf_freq) >= 0);
-    UHD_ASSERT_THROW(fp_compare_epsilon<double>(std::abs(rf_freq - _desired_rf_freq[dir]))
+    UHD_ASSERT_THROW(freq_compare_epsilon(rf_freq) >= 0);
+    UHD_ASSERT_THROW(freq_compare_epsilon(std::abs(rf_freq - _desired_rf_freq[dir]))
                      <= _master_clock_rate / 2);
     if (dir == RX_DIRECTION) {
         radio_control_impl::set_rx_frequency(rf_freq, chan);
diff --git a/host/lib/usrp/dboard/rhodium/rhodium_bands.cpp b/host/lib/usrp/dboard/rhodium/rhodium_bands.cpp
index 73f1bbe0c..6c16a7d7f 100644
--- a/host/lib/usrp/dboard/rhodium/rhodium_bands.cpp
+++ b/host/lib/usrp/dboard/rhodium/rhodium_bands.cpp
@@ -69,7 +69,7 @@ constexpr double RHODIUM_TX_BAND7_MIN_FREQ = 4100e6;
 rhodium_radio_control_impl::rx_band rhodium_radio_control_impl::_map_freq_to_rx_band(
     const double freq)
 {
-    auto freq_compare = fp_compare_epsilon<double>(freq, RHODIUM_FREQ_COMPARE_EPSILON);
+    const auto freq_compare = freq_compare_epsilon(freq);
 
     if (freq_compare < RHODIUM_RX_BAND0_MIN_FREQ) {
         return rx_band::RX_BAND_INVALID;
@@ -97,7 +97,7 @@ rhodium_radio_control_impl::rx_band rhodium_radio_control_impl::_map_freq_to_rx_
 rhodium_radio_control_impl::tx_band rhodium_radio_control_impl::_map_freq_to_tx_band(
     const double freq)
 {
-    auto freq_compare = fp_compare_epsilon<double>(freq, RHODIUM_FREQ_COMPARE_EPSILON);
+    const auto freq_compare = freq_compare_epsilon(freq);
 
     if (freq_compare < RHODIUM_TX_BAND0_MIN_FREQ) {
         return tx_band::TX_BAND_INVALID;
diff --git a/host/lib/usrp/dboard/rhodium/rhodium_constants.hpp b/host/lib/usrp/dboard/rhodium/rhodium_constants.hpp
index cc6a70dc3..7043c50af 100644
--- a/host/lib/usrp/dboard/rhodium/rhodium_constants.hpp
+++ b/host/lib/usrp/dboard/rhodium/rhodium_constants.hpp
@@ -12,8 +12,6 @@
 #include <string>
 #include <vector>
 
-static constexpr double RHODIUM_FREQ_COMPARE_EPSILON = 1e-5;
-
 static constexpr size_t NUM_RHODIUM_RADIO_RATES = 3;
 
 static constexpr std::array<double, NUM_RHODIUM_RADIO_RATES> RHODIUM_RADIO_RATES = {
diff --git a/host/lib/usrp/dboard/rhodium/rhodium_cpld_ctrl.cpp b/host/lib/usrp/dboard/rhodium/rhodium_cpld_ctrl.cpp
index b95f03983..099b5d132 100644
--- a/host/lib/usrp/dboard/rhodium/rhodium_cpld_ctrl.cpp
+++ b/host/lib/usrp/dboard/rhodium/rhodium_cpld_ctrl.cpp
@@ -263,7 +263,7 @@ void rhodium_cpld_ctrl::set_rx_lo_path(const double freq, const bool defer_commi
     UHD_LOG_TRACE("RH_CPLD", "Configuring RX LO filter and settings. freq=" << freq);
     std::lock_guard<std::mutex> l(_set_mutex);
 
-    auto freq_compare = fp_compare_epsilon<double>(freq, RHODIUM_FREQ_COMPARE_EPSILON);
+    const auto freq_compare = freq_compare_epsilon(freq);
 
     if (freq_compare < RX_DEMOD_ADJ_1500OHM_THRESHOLD) {
         _regs.rx_demod_adj =
@@ -296,7 +296,7 @@ void rhodium_cpld_ctrl::set_tx_lo_path(const double freq, const bool defer_commi
     UHD_LOG_TRACE("RH_CPLD", "Configuring TX LO filter and settings. freq=" << freq);
     std::lock_guard<std::mutex> l(_set_mutex);
 
-    auto freq_compare = fp_compare_epsilon<double>(freq, RHODIUM_FREQ_COMPARE_EPSILON);
+    const auto freq_compare = freq_compare_epsilon(freq);
 
     if (freq_compare < RHODIUM_LO_0_9_GHZ_LPF_THRESHOLD_FREQ) {
         _regs.tx_lo_filter_sel =
diff --git a/host/lib/usrp/x300/x300_clock_ctrl.cpp b/host/lib/usrp/x300/x300_clock_ctrl.cpp
index e80335d9b..fc0094866 100644
--- a/host/lib/usrp/x300/x300_clock_ctrl.cpp
+++ b/host/lib/usrp/x300/x300_clock_ctrl.cpp
@@ -585,9 +585,11 @@ private:
             } else if (math::frequencies_are_equal(_master_clock_rate, 120e6)) {
                 /* 10MHz reference, 120 MHz master clock rate, Zero Delay */
                 clocking_mode = m10M_120M_ZDEL;
-            } else if (fp_compare_epsilon<double>(_master_clock_rate)
+            } else if (fp_compare_delta<double>(
+                           _master_clock_rate, math::FREQ_COMPARISON_DELTA_HZ)
                            >= uhd::usrp::x300::MIN_TICK_RATE
-                       && fp_compare_epsilon<double>(_master_clock_rate)
+                       && fp_compare_delta<double>(
+                              _master_clock_rate, math::FREQ_COMPARISON_DELTA_HZ)
                               <= uhd::usrp::x300::MAX_TICK_RATE) {
                 /* 10MHz reference, attempt to automatically configure PLL
                  * for arbitrary master clock rate, Zero Delay */