Bug 1265399 - Replace 0.7071 with sqrt(0.5) in downmixing equations; r=padenot

MozReview-Commit-ID: 8hiiqJ0yIxm

--HG--
extra : rebase_source : cd9c99dd903edf68203cb466e33a2877f418285e

dom/media/AudioChannelFormat.h

@@ -65,6 +65,8 @@ GetAudioChannelsSuperset(uint32_t aChannels1, uint32_t aChannels2);
  * every input channel is multiplied by the same coefficient for every output
  * channel it contributes to.
  */
+const float SQRT_ONE_HALF = sqrt(0.5);
+
 struct DownMixMatrix {
   // Every input channel c is copied to output channel mInputDestination[c]
   // after multiplying by mInputCoefficient[c].
@@ -83,19 +85,19 @@ gDownMixMatrices[CUSTOM_CHANNEL_LAYOUTS*(CUSTOM_CHANNEL_LAYOUTS - 1)/2] =
   { { 0, IGNORE, IGNORE }, IGNORE, { 1.0f, IGNORE_F, IGNORE_F } },
   { { 0, 0, 0, 0 }, IGNORE, { 0.25f, 0.25f, 0.25f, 0.25f } },
   { { 0, IGNORE, IGNORE, IGNORE, IGNORE }, IGNORE, { 1.0f, IGNORE_F, IGNORE_F, IGNORE_F, IGNORE_F } },
-  { { 0, 0, 0, IGNORE, 0, 0 }, IGNORE, { 0.7071f, 0.7071f, 1.0f, IGNORE_F, 0.5f, 0.5f } },
+  { { 0, 0, 0, IGNORE, 0, 0 }, IGNORE, { SQRT_ONE_HALF, SQRT_ONE_HALF, 1.0f, IGNORE_F, 0.5f, 0.5f } },
   // Downmixes to stereo
   { { 0, 1, IGNORE }, IGNORE, { 1.0f, 1.0f, IGNORE_F } },
   { { 0, 1, 0, 1 }, IGNORE, { 0.5f, 0.5f, 0.5f, 0.5f } },
   { { 0, 1, IGNORE, IGNORE, IGNORE }, IGNORE, { 1.0f, 1.0f, IGNORE_F, IGNORE_F, IGNORE_F } },
-  { { 0, 1, 0, IGNORE, 0, 1 }, 1, { 1.0f, 1.0f, 0.7071f, IGNORE_F, 0.7071f, 0.7071f } },
+  { { 0, 1, 0, IGNORE, 0, 1 }, 1, { 1.0f, 1.0f, SQRT_ONE_HALF, IGNORE_F, SQRT_ONE_HALF, SQRT_ONE_HALF } },
   // Downmixes to 3-channel
   { { 0, 1, 2, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, IGNORE_F } },
   { { 0, 1, 2, IGNORE, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, IGNORE_F, IGNORE_F } },
   { { 0, 1, 2, IGNORE, IGNORE, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, IGNORE_F, IGNORE_F, IGNORE_F } },
   // Downmixes to quad
   { { 0, 1, 2, 3, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, 1.0f, IGNORE_F } },
-  { { 0, 1, 0, IGNORE, 2, 3 }, 1, { 1.0f, 1.0f, 0.7071f, IGNORE_F, 1.0f, 1.0f } },
+  { { 0, 1, 0, IGNORE, 2, 3 }, 1, { 1.0f, 1.0f, SQRT_ONE_HALF, IGNORE_F, 1.0f, 1.0f } },
   // Downmixes to 5-channel
   { { 0, 1, 2, 3, 4, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, IGNORE_F } }
 };