libobs/media-io: Add common audio math functions

This adds functions specific to audio math, which at the moment is just
converting to and from decibel and multiple.

libobs/CMakeLists.txt

@@ -180,6 +180,7 @@ set(libobs_mediaio_HEADERS
 	media-io/media-io-defs.h
 	media-io/video-io.h
 	media-io/audio-io.h
+	media-io/audio-math.h
 	media-io/video-frame.h
 	media-io/format-conversion.h
 	media-io/audio-resampler.h

libobs/media-io/audio-math.h

@@ -0,0 +1,43 @@
+/******************************************************************************
+    Copyright (C) 2015 by Hugh Bailey <[email protected]>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+******************************************************************************/
+
+#pragma once
+
+#include "../util/c99defs.h"
+#include <math.h>
+
+#ifdef _MSC_VER
+#include <float.h>
+
+#pragma warning(push)
+#pragma warning(disable : 4056)
+#pragma warning(disable : 4756)
+#endif
+
+static inline float mul_to_db(const float mul)
+{
+	return (mul == 0.0f) ? -INFINITY : (20.0f * log10f(mul));
+}
+
+static inline float db_to_mul(const float db)
+{
+	return isfinite((double)db) ? powf(10.0f, db / 20.0f) : 0.0f;
+}
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif