| /* |
| * Copyright (c) 2012 The WebRTC project authors. All Rights Reserved. |
| * |
| * Use of this source code is governed by a BSD-style license |
| * that can be found in the LICENSE file in the root of the source |
| * tree. An additional intellectual property rights grant can be found |
| * in the file PATENTS. All contributing project authors may |
| * be found in the AUTHORS file in the root of the source tree. |
| */ |
| |
| #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h" |
| |
| #include "webrtc/base/checks.h" |
| |
| size_t WebRtcSpl_AutoCorrelation(const int16_t* in_vector, |
| size_t in_vector_length, |
| size_t order, |
| int32_t* result, |
| int* scale) { |
| int32_t sum = 0; |
| size_t i = 0, j = 0; |
| int16_t smax = 0; |
| int scaling = 0; |
| |
| RTC_DCHECK_LE(order, in_vector_length); |
| |
| // Find the maximum absolute value of the samples. |
| smax = WebRtcSpl_MaxAbsValueW16(in_vector, in_vector_length); |
| |
| // In order to avoid overflow when computing the sum we should scale the |
| // samples so that (in_vector_length * smax * smax) will not overflow. |
| if (smax == 0) { |
| scaling = 0; |
| } else { |
| // Number of bits in the sum loop. |
| int nbits = WebRtcSpl_GetSizeInBits((uint32_t)in_vector_length); |
| // Number of bits to normalize smax. |
| int t = WebRtcSpl_NormW32(WEBRTC_SPL_MUL(smax, smax)); |
| |
| if (t > nbits) { |
| scaling = 0; |
| } else { |
| scaling = nbits - t; |
| } |
| } |
| |
| // Perform the actual correlation calculation. |
| for (i = 0; i < order + 1; i++) { |
| sum = 0; |
| /* Unroll the loop to improve performance. */ |
| for (j = 0; i + j + 3 < in_vector_length; j += 4) { |
| sum += (in_vector[j + 0] * in_vector[i + j + 0]) >> scaling; |
| sum += (in_vector[j + 1] * in_vector[i + j + 1]) >> scaling; |
| sum += (in_vector[j + 2] * in_vector[i + j + 2]) >> scaling; |
| sum += (in_vector[j + 3] * in_vector[i + j + 3]) >> scaling; |
| } |
| for (; j < in_vector_length - i; j++) { |
| sum += (in_vector[j] * in_vector[i + j]) >> scaling; |
| } |
| *result++ = sum; |
| } |
| |
| *scale = scaling; |
| return order + 1; |
| } |