Merge from Chromium at DEPS revision 237746

This commit was generated by merge_to_master.py.

Change-Id: I8997af4cddfeb09a7c26f7e8e672c712cab461ea

1 files changed, 79 insertions, 0 deletions

diff --git a/media/base/simd/vector_math_sse.cc b/media/base/simd/vector_math_sse.cc
index 39bcaa0c19..c2121225cd 100644
--- a/media/base/simd/vector_math_sse.cc
+++ b/media/base/simd/vector_math_sse.cc
@@ -4,6 +4,8 @@
 
 #include "media/base/vector_math_testing.h"
 
+#include <algorithm>
+
 #include <xmmintrin.h>  // NOLINT
 
 namespace media {
@@ -35,5 +37,82 @@ void FMAC_SSE(const float src[], float scale, int len, float dest[]) {
     dest[i] += src[i] * scale;
 }
 
+// Convenience macro to extract float 0 through 3 from the vector |a|.  This is
+// needed because compilers other than clang don't support access via
+// operator[]().
+#define EXTRACT_FLOAT(a, i) \
+    (i == 0 ? \
+         _mm_cvtss_f32(a) : \
+         _mm_cvtss_f32(_mm_shuffle_ps(a, a, i)))
+
+std::pair<float, float> EWMAAndMaxPower_SSE(
+    float initial_value, const float src[], int len, float smoothing_factor) {
+  // When the recurrence is unrolled, we see that we can split it into 4
+  // separate lanes of evaluation:
+  //
+  // y[n] = a(S[n]^2) + (1-a)(y[n-1])
+  //      = a(S[n]^2) + (1-a)^1(aS[n-1]^2) + (1-a)^2(aS[n-2]^2) + ...
+  //      = z[n] + (1-a)^1(z[n-1]) + (1-a)^2(z[n-2]) + (1-a)^3(z[n-3])
+  //
+  // where z[n] = a(S[n]^2) + (1-a)^4(z[n-4]) + (1-a)^8(z[n-8]) + ...
+  //
+  // Thus, the strategy here is to compute z[n], z[n-1], z[n-2], and z[n-3] in
+  // each of the 4 lanes, and then combine them to give y[n].
+
+  const int rem = len % 4;
+  const int last_index = len - rem;
+
+  const __m128 smoothing_factor_x4 = _mm_set_ps1(smoothing_factor);
+  const float weight_prev = 1.0f - smoothing_factor;
+  const __m128 weight_prev_x4 = _mm_set_ps1(weight_prev);
+  const __m128 weight_prev_squared_x4 =
+      _mm_mul_ps(weight_prev_x4, weight_prev_x4);
+  const __m128 weight_prev_4th_x4 =
+      _mm_mul_ps(weight_prev_squared_x4, weight_prev_squared_x4);
+
+  // Compute z[n], z[n-1], z[n-2], and z[n-3] in parallel in lanes 3, 2, 1 and
+  // 0, respectively.
+  __m128 max_x4 = _mm_setzero_ps();
+  __m128 ewma_x4 = _mm_setr_ps(0.0f, 0.0f, 0.0f, initial_value);
+  int i;
+  for (i = 0; i < last_index; i += 4) {
+    ewma_x4 = _mm_mul_ps(ewma_x4, weight_prev_4th_x4);
+    const __m128 sample_x4 = _mm_load_ps(src + i);
+    const __m128 sample_squared_x4 = _mm_mul_ps(sample_x4, sample_x4);
+    max_x4 = _mm_max_ps(max_x4, sample_squared_x4);
+    // Note: The compiler optimizes this to a single multiply-and-accumulate
+    // instruction:
+    ewma_x4 = _mm_add_ps(ewma_x4,
+                         _mm_mul_ps(sample_squared_x4, smoothing_factor_x4));
+  }
+
+  // y[n] = z[n] + (1-a)^1(z[n-1]) + (1-a)^2(z[n-2]) + (1-a)^3(z[n-3])
+  float ewma = EXTRACT_FLOAT(ewma_x4, 3);
+  ewma_x4 = _mm_mul_ps(ewma_x4, weight_prev_x4);
+  ewma += EXTRACT_FLOAT(ewma_x4, 2);
+  ewma_x4 = _mm_mul_ps(ewma_x4, weight_prev_x4);
+  ewma += EXTRACT_FLOAT(ewma_x4, 1);
+  ewma_x4 = _mm_mul_ss(ewma_x4, weight_prev_x4);
+  ewma += EXTRACT_FLOAT(ewma_x4, 0);
+
+  // Fold the maximums together to get the overall maximum.
+  max_x4 = _mm_max_ps(max_x4,
+                      _mm_shuffle_ps(max_x4, max_x4, _MM_SHUFFLE(3, 3, 1, 1)));
+  max_x4 = _mm_max_ss(max_x4, _mm_shuffle_ps(max_x4, max_x4, 2));
+
+  std::pair<float, float> result(ewma, EXTRACT_FLOAT(max_x4, 0));
+
+  // Handle remaining values at the end of |src|.
+  for (; i < len; ++i) {
+    result.first *= weight_prev;
+    const float sample = src[i];
+    const float sample_squared = sample * sample;
+    result.first += sample_squared * smoothing_factor;
+    result.second = std::max(result.second, sample_squared);
+  }
+
+  return result;
+}
+
 }  // namespace vector_math
 }  // namespace media