core: remove boost::math in favor of std cmath

YA Boost removal!!!

Justification
---
const int if_freq_sign = boost::math::sign(fe_conn.get_if_freq());
_dsp_freq_offset = if_freq * (-if_freq_sign);
// boost::math::sign : 1 if x > 0, -1 if x < 0, and 0 if x is zero.
// ==> if if_freq_sign > 0 then * by -1 else +1 (effectively)

// std::signbit : true if arg is negative, false otherwise
// ==> need 'not' of input argument to invert for same result as prior algorithm
double fe_if_freq = fe_conn.get_if_freq();
if (!std::signbit(fe_if_freq)) {
  if_freq *= -1.0;
}
---
The above should result in the same algorithm except possibly
if fe_if_freq is exactly 0.0 in which case the results might be
off by the sign (+0.0 versus -0.0).

2 files changed, 16 insertions, 13 deletions

diff --git a/host/lib/usrp/cores/rx_dsp_core_3000.cpp b/host/lib/usrp/cores/rx_dsp_core_3000.cpp
index 879748fa2..1c15180ae 100644
--- a/host/lib/usrp/cores/rx_dsp_core_3000.cpp
+++ b/host/lib/usrp/cores/rx_dsp_core_3000.cpp
@@ -8,7 +8,6 @@
 #include <uhd/exception.hpp>
 #include <uhd/types/dict.hpp>
 #include <uhd/utils/log.hpp>
-#include <uhd/utils/math.hpp>
 #include <uhd/utils/safe_call.hpp>
 #include <uhdlib/usrp/cores/dsp_core_utils.hpp>
 #include <uhdlib/usrp/cores/rx_dsp_core_3000.hpp>
@@ -81,19 +80,21 @@ public:
         _iface->poke32(REG_DSP_RX_MUX, reg_val);
 
         if (fe_conn.get_sampling_mode() == uhd::usrp::fe_connection_t::HETERODYNE) {
-            // 1. Remember the sign of the IF frequency.
-            //   It will be discarded in the next step
-            int if_freq_sign = boost::math::sign(fe_conn.get_if_freq());
+            // 1. Remember the IF frequency
+            const double fe_if_freq = fe_conn.get_if_freq();
             // 2. Map IF frequency to the range [0, _tick_rate)
-            double if_freq = std::abs(std::fmod(fe_conn.get_if_freq(), _tick_rate));
-            // 3. Map IF frequency to the range [-_tick_rate/2, _tick_rate/2)
+            double if_freq = std::abs(std::fmod(fe_if_freq, _tick_rate));
+            // 3. Map IF frequency to the range [-_tick_rate/2, _tick_rate/2]
             //   This is the aliased frequency
             if (if_freq > (_tick_rate / 2.0)) {
                 if_freq -= _tick_rate;
             }
             // 4. Set DSP offset to spin the signal in the opposite
             //   direction as the aliased frequency
-            _dsp_freq_offset = if_freq * (-if_freq_sign);
+            if (!std::signbit(fe_if_freq)) {
+                if_freq *= -1.0;
+            }
+            _dsp_freq_offset = if_freq;
         } else {
             _dsp_freq_offset = 0.0;
         }
diff --git a/host/lib/usrp/cores/rx_frontend_core_3000.cpp b/host/lib/usrp/cores/rx_frontend_core_3000.cpp
index eef25f27d..b9d908534 100644
--- a/host/lib/usrp/cores/rx_frontend_core_3000.cpp
+++ b/host/lib/usrp/cores/rx_frontend_core_3000.cpp
@@ -119,19 +119,21 @@ public:
 
         UHD_ASSERT_THROW(_adc_rate != 0.0)
         if (fe_conn.get_sampling_mode() == fe_connection_t::HETERODYNE) {
-            // 1. Remember the sign of the IF frequency.
-            //   It will be discarded in the next step
-            const int if_freq_sign = boost::math::sign(fe_conn.get_if_freq());
+            // 1. Remember the IF frequency
+            const double fe_if_freq = fe_conn.get_if_freq();
             // 2. Map IF frequency to the range [0, _adc_rate)
-            double if_freq = std::abs(std::fmod(fe_conn.get_if_freq(), _adc_rate));
-            // 3. Map IF frequency to the range [-_adc_rate/2, _adc_rate/2)
+            double if_freq = std::abs(std::fmod(fe_if_freq, _adc_rate));
+            // 3. Map IF frequency to the range [-_adc_rate/2, _adc_rate/2]
             //   This is the aliased frequency
             if (if_freq > (_adc_rate / 2.0)) {
                 if_freq -= _adc_rate;
             }
             // 4. Set DSP offset to spin the signal in the opposite
             //   direction as the aliased frequency
-            const double cordic_freq = if_freq * (-if_freq_sign);
+            if (!std::signbit(fe_if_freq)) {
+                if_freq *= -1.0;
+            }
+            const double cordic_freq = if_freq;
             UHD_ASSERT_THROW(uhd::math::fp_compare::fp_compare_epsilon<double>(4.0)
                              == std::abs(_adc_rate / cordic_freq));