Bug 865256 - Part 3a: Add AudioBufferPeakValue utility. r=ehsan

From 6c057c02970c79d620527d08bc3755491c99b1d3 Mon Sep 17 00:00:00 2001
This is an equivalent, C-only implementation of blink's
VectorMath::maxmgv or Apple's vDSP_maxmgv. It finds the
maximum absolute value of the elements in a float buffer.
Used by blink's PeriodicWave implementation for normalization.

content/media/AudioNodeEngine.cpp

@@ -125,6 +125,19 @@ BufferComplexMultiply(const float* aInput,
   }
 }
 
+float
+AudioBufferPeakValue(const float *aInput, uint32_t aSize)
+{
+  float max = 0.0f;
+  for (uint32_t i = 0; i < aSize; i++) {
+    float mag = fabs(aInput[i]);
+    if (mag > max) {
+      max = mag;
+    }
+  }
+  return max;
+}
+
 void
 AudioBlockCopyChannelWithScale(const float aInput[WEBAUDIO_BLOCK_SIZE],
                                const float aScale[WEBAUDIO_BLOCK_SIZE],

content/media/AudioNodeEngine.h

@@ -134,6 +134,11 @@ void BufferComplexMultiply(const float* aInput,
                            float* aOutput,
                            uint32_t aSize);
 
+/**
+ * Vector maximum element magnitude ( max(abs(aInput)) ).
+ */
+float AudioBufferPeakValue(const float* aInput, uint32_t aSize);
+
 /**
  * In place gain. aScale == 1.0f should be optimized.
  */