1 /* 2 * Copyright (c) 2012 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h" 12 13 #include <assert.h> 14 15 size_t WebRtcSpl_AutoCorrelation(const int16_t* in_vector, 16 size_t in_vector_length, 17 size_t order, 18 int32_t* result, 19 int* scale) { 20 int32_t sum = 0; 21 size_t i = 0, j = 0; 22 int16_t smax = 0; 23 int scaling = 0; 24 25 assert(order <= in_vector_length); 26 27 // Find the maximum absolute value of the samples. 28 smax = WebRtcSpl_MaxAbsValueW16(in_vector, in_vector_length); 29 30 // In order to avoid overflow when computing the sum we should scale the 31 // samples so that (in_vector_length * smax * smax) will not overflow. 32 if (smax == 0) { 33 scaling = 0; 34 } else { 35 // Number of bits in the sum loop. 36 int nbits = WebRtcSpl_GetSizeInBits((uint32_t)in_vector_length); 37 // Number of bits to normalize smax. 38 int t = WebRtcSpl_NormW32(WEBRTC_SPL_MUL(smax, smax)); 39 40 if (t > nbits) { 41 scaling = 0; 42 } else { 43 scaling = nbits - t; 44 } 45 } 46 47 // Perform the actual correlation calculation. 48 for (i = 0; i < order + 1; i++) { 49 sum = 0; 50 /* Unroll the loop to improve performance. */ 51 for (j = 0; i + j + 3 < in_vector_length; j += 4) { 52 sum += (in_vector[j + 0] * in_vector[i + j + 0]) >> scaling; 53 sum += (in_vector[j + 1] * in_vector[i + j + 1]) >> scaling; 54 sum += (in_vector[j + 2] * in_vector[i + j + 2]) >> scaling; 55 sum += (in_vector[j + 3] * in_vector[i + j + 3]) >> scaling; 56 } 57 for (; j < in_vector_length - i; j++) { 58 sum += (in_vector[j] * in_vector[i + j]) >> scaling; 59 } 60 *result++ = sum; 61 } 62 63 *scale = scaling; 64 return order + 1; 65 } 66
