Reland of Added ARM Neon SIMD optimizations for AEC3

webrtc/modules/audio_processing/aec3/vector_math.h

Index: webrtc/modules/audio_processing/aec3/vector_math.h
diff --git a/webrtc/modules/audio_processing/aec3/vector_math.h b/webrtc/modules/audio_processing/aec3/vector_math.h
index afd4262b6ba07ee6d58389ad7e991176360ba167..b943f2beddf91989544409338daaeb2cb61ddbc1 100644
--- a/webrtc/modules/audio_processing/aec3/vector_math.h
+++ b/webrtc/modules/audio_processing/aec3/vector_math.h
@@ -12,6 +12,9 @@
 #define WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_VECTOR_MATH_H_
 
 #include "webrtc/typedefs.h"
+#if defined(WEBRTC_HAS_NEON)
+#include <arm_neon.h>
+#endif
 #if defined(WEBRTC_ARCH_X86_FAMILY)
 #include <emmintrin.h>
 #endif
@@ -53,6 +56,51 @@
         }
       } break;
 #endif
+#if defined(WEBRTC_HAS_NEON)
+      case Aec3Optimization::kNeon: {
+        const int x_size = static_cast<int>(x.size());
+        const int vector_limit = x_size >> 2;
+
+        int j = 0;
+        for (; j < vector_limit * 4; j += 4) {
+          float32x4_t g = vld1q_f32(&x[j]);
+#if !defined(WEBRTC_ARCH_ARM64)
+          float32x4_t y = vrsqrteq_f32(g);
+
+          // Code to handle sqrt(0).
+          // If the input to sqrtf() is zero, a zero will be returned.
+          // If the input to vrsqrteq_f32() is zero, positive infinity is
+          // returned.
+          const uint32x4_t vec_p_inf = vdupq_n_u32(0x7F800000);
+          // check for divide by zero
+          const uint32x4_t div_by_zero =
+              vceqq_u32(vec_p_inf, vreinterpretq_u32_f32(y));
+          // zero out the positive infinity results
+          y = vreinterpretq_f32_u32(
+              vandq_u32(vmvnq_u32(div_by_zero), vreinterpretq_u32_f32(y)));
+          // from arm documentation
+          // The Newton-Raphson iteration:
+          //     y[n+1] = y[n] * (3 - d * (y[n] * y[n])) / 2)
+          // converges to (1/√d) if y0 is the result of VRSQRTE applied to d.
+          //
+          // Note: The precision did not improve after 2 iterations.
+          for (int i = 0; i < 2; i++) {
+            y = vmulq_f32(vrsqrtsq_f32(vmulq_f32(y, y), g), y);
+          }
+          // sqrt(g) = g * 1/sqrt(g)
+          g = vmulq_f32(g, y);
+#else
+          g = vsqrtq_f32(g);
+#endif
+          vst1q_f32(&x[j], g);
+        }
+
+        for (; j < x_size; ++j) {
+          x[j] = sqrtf(x[j]);
+        }
+      }
+#endif
+      break;
       default:
         std::for_each(x.begin(), x.end(), [](float& a) { a = sqrtf(a); });
     }
@@ -83,6 +131,24 @@
         }
       } break;
 #endif
+#if defined(WEBRTC_HAS_NEON)
+      case Aec3Optimization::kNeon: {
+        const int x_size = static_cast<int>(x.size());
+        const int vector_limit = x_size >> 2;
+
+        int j = 0;
+        for (; j < vector_limit * 4; j += 4) {
+          const float32x4_t x_j = vld1q_f32(&x[j]);
+          const float32x4_t y_j = vld1q_f32(&y[j]);
+          const float32x4_t z_j = vmulq_f32(x_j, y_j);
+          vst1q_f32(&z[j], z_j);
+        }
+
+        for (; j < x_size; ++j) {
+          z[j] = x[j] * y[j];
+        }
+      } break;
+#endif
       default:
         std::transform(x.begin(), x.end(), y.begin(), z.begin(),
                        std::multiplies<float>());
@@ -111,6 +177,24 @@
         }
       } break;
 #endif
+#if defined(WEBRTC_HAS_NEON)
+      case Aec3Optimization::kNeon: {
+        const int x_size = static_cast<int>(x.size());
+        const int vector_limit = x_size >> 2;
+
+        int j = 0;
+        for (; j < vector_limit * 4; j += 4) {
+          const float32x4_t x_j = vld1q_f32(&x[j]);
+          float32x4_t z_j = vld1q_f32(&z[j]);
+          z_j = vaddq_f32(z_j, x_j);
+          vst1q_f32(&z[j], z_j);
+        }
+
+        for (; j < x_size; ++j) {
+          z[j] += x[j];
+        }
+      } break;
+#endif
       default:
         std::transform(x.begin(), x.end(), z.begin(), z.begin(),
                        std::plus<float>());