Add SSE and NEON intrinsics for WSOLA's MultiChannelDotProduct().

media/filters/wsola_internals.cc

Index: media/filters/wsola_internals.cc
diff --git a/media/filters/wsola_internals.cc b/media/filters/wsola_internals.cc
index a247df91c5cd761093ff1c0753f648ef0d372911..9e12f032f3cc021a151c933aec88a2fe82e31bf7 100644
--- a/media/filters/wsola_internals.cc
+++ b/media/filters/wsola_internals.cc
@@ -15,6 +15,14 @@
 #include "base/logging.h"
 #include "media/base/audio_bus.h"
 
+#if defined(ARCH_CPU_X86_FAMILY)
+#define USE_SIMD 1
+#include <xmmintrin.h>
+#elif defined(ARCH_CPU_ARM_FAMILY) && defined(USE_NEON)
+#define USE_SIMD 1
+#include <arm_neon.h>
+#endif
+
 namespace media {
 
 namespace internal {
@@ -48,13 +56,55 @@ void MultiChannelDotProduct(const AudioBus* a,
   DCHECK_LE(frame_offset_a + num_frames, a->frames());
   DCHECK_LE(frame_offset_b + num_frames, b->frames());
 
+// SIMD optimized variants can provide a massive speedup to this operation.
+#if defined(USE_SIMD)
+  const int rem = num_frames % 4;
+  const int last_index = num_frames - rem;
+  const int channels = a->channels();
+  for (int ch = 0; ch < channels; ++ch) {
+    const float* a_src = a->channel(ch) + frame_offset_a;
+    const float* b_src = b->channel(ch) + frame_offset_b;
+
+#if defined(ARCH_CPU_X86_FAMILY)
+    // First sum all components.
+    __m128 m_sum = _mm_setzero_ps();
+    for (int s = 0; s < last_index; s += 4) {
+      m_sum = _mm_add_ps(
+          m_sum, _mm_mul_ps(_mm_loadu_ps(a_src + s), _mm_loadu_ps(b_src + s)));
+    }
+
+    // Reduce to a single float for this channel. Sadly, SSE1,2 doesn't have a
+    // horizontal sum function, so we have to condense manually.
+    m_sum = _mm_add_ps(_mm_movehl_ps(m_sum, m_sum), m_sum);
+    _mm_store_ss(dot_product + ch,
+                 _mm_add_ss(m_sum, _mm_shuffle_ps(m_sum, m_sum, 1)));
+#elif defined(ARCH_CPU_ARM_FAMILY)
+    // First sum all components.
+    float32x4_t m_sum = vmovq_n_f32(0);
+    for (int s = 0; s < last_index; s += 4)
+      m_sum = vmlaq_f32(m_sum, vld1q_f32(a_src + s), vld1q_f32(b_src + s));
+
+    // Reduce to a single float for this channel.
+    float32x2_t m_half = vadd_f32(vget_high_f32(m_sum), vget_low_f32(m_sum));
+    dot_product[ch] = vget_lane_f32(vpadd_f32(m_half, m_half), 0);
+#endif
+  }
+
+  if (!rem)
+    return;
+  num_frames = rem;
+  frame_offset_a += last_index;
+  frame_offset_b += last_index;
+#else
   memset(dot_product, 0, sizeof(*dot_product) * a->channels());
+#endif  // defined(USE_SIMD)
+
+  // C version is required to handle remainder of frames (% 4 != 0)
   for (int k = 0; k < a->channels(); ++k) {
     const float* ch_a = a->channel(k) + frame_offset_a;
     const float* ch_b = b->channel(k) + frame_offset_b;
-    for (int n = 0; n < num_frames; ++n) {
+    for (int n = 0; n < num_frames; ++n)
       dot_product[k] += *ch_a++ * *ch_b++;
-    }
   }
 }