treewide: get rid of C math function usage

Boost does not seem to offer an overload for lrint.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/mixer/plugins/AlsaMixerPlugin.cxx

@@ -26,6 +26,7 @@
 #include "event/Call.hxx"
 #include "util/ASCII.hxx"
 #include "util/Domain.hxx"
+#include "util/Math.hxx"
 #include "util/RuntimeError.hxx"
 #include "Log.hxx"
 
@@ -35,8 +36,6 @@ extern "C" {
 
 #include <alsa/asoundlib.h>
 
-#include <math.h>
-
 #define VOLUME_MIXER_ALSA_DEFAULT		"default"
 #define VOLUME_MIXER_ALSA_CONTROL_DEFAULT	"PCM"
 static constexpr unsigned VOLUME_MIXER_ALSA_INDEX_DEFAULT = 0;

src/mixer/plugins/SoftwareMixerPlugin.cxx

@@ -23,8 +23,9 @@
 #include "pcm/Volume.hxx"
 
 #include <cassert>
+#include <cmath>
 
-#include <math.h>
+#include <assert.h>
 
 class SoftwareMixer final : public Mixer {
 	Filter *filter = nullptr;
@@ -74,7 +75,7 @@ PercentVolumeToSoftwareVolume(unsigned volume) noexcept
 	if (volume >= 100)
 		return PCM_VOLUME_1;
 	else if (volume > 0)
-		return pcm_float_to_volume((exp(volume / 25.0) - 1) /
+		return pcm_float_to_volume((std::exp(volume / 25.0) - 1) /
 					   (54.5981500331F - 1));
 	else
 		return 0;