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| 56 | mjames | 1 | /* ---------------------------------------------------------------------- |
| 2 | * Project: CMSIS DSP Library |
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| 3 | * Title: arm_rms_q31.c |
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| 4 | * Description: Root Mean Square of the elements of a Q31 vector |
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| 5 | * |
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| 6 | * $Date: 27. January 2017 |
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| 7 | * $Revision: V.1.5.1 |
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| 8 | * |
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| 9 | * Target Processor: Cortex-M cores |
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| 10 | * -------------------------------------------------------------------- */ |
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| 11 | /* |
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| 12 | * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved. |
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| 13 | * |
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| 14 | * SPDX-License-Identifier: Apache-2.0 |
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| 15 | * |
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| 16 | * Licensed under the Apache License, Version 2.0 (the License); you may |
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| 17 | * not use this file except in compliance with the License. |
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| 18 | * You may obtain a copy of the License at |
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| 19 | * |
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| 20 | * www.apache.org/licenses/LICENSE-2.0 |
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| 21 | * |
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| 22 | * Unless required by applicable law or agreed to in writing, software |
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| 23 | * distributed under the License is distributed on an AS IS BASIS, WITHOUT |
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| 24 | * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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| 25 | * See the License for the specific language governing permissions and |
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| 26 | * limitations under the License. |
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| 27 | */ |
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| 28 | |||
| 29 | #include "arm_math.h" |
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| 30 | |||
| 31 | /** |
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| 32 | * @addtogroup RMS |
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| 33 | * @{ |
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| 34 | */ |
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| 35 | |||
| 36 | |||
| 37 | /** |
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| 38 | * @brief Root Mean Square of the elements of a Q31 vector. |
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| 39 | * @param[in] *pSrc points to the input vector |
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| 40 | * @param[in] blockSize length of the input vector |
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| 41 | * @param[out] *pResult rms value returned here |
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| 42 | * @return none. |
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| 43 | * |
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| 44 | * @details |
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| 45 | * <b>Scaling and Overflow Behavior:</b> |
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| 46 | * |
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| 47 | *\par |
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| 48 | * The function is implemented using an internal 64-bit accumulator. |
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| 49 | * The input is represented in 1.31 format, and intermediate multiplication |
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| 50 | * yields a 2.62 format. |
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| 51 | * The accumulator maintains full precision of the intermediate multiplication results, |
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| 52 | * but provides only a single guard bit. |
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| 53 | * There is no saturation on intermediate additions. |
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| 54 | * If the accumulator overflows, it wraps around and distorts the result. |
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| 55 | * In order to avoid overflows completely, the input signal must be scaled down by |
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| 56 | * log2(blockSize) bits, as a total of blockSize additions are performed internally. |
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| 57 | * Finally, the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value. |
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| 58 | * |
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| 59 | */ |
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| 60 | |||
| 61 | void arm_rms_q31( |
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| 62 | q31_t * pSrc, |
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| 63 | uint32_t blockSize, |
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| 64 | q31_t * pResult) |
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| 65 | { |
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| 66 | q63_t sum = 0; /* accumulator */ |
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| 67 | q31_t in; /* Temporary variable to store the input */ |
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| 68 | uint32_t blkCnt; /* loop counter */ |
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| 69 | |||
| 70 | #if defined (ARM_MATH_DSP) |
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| 71 | /* Run the below code for Cortex-M4 and Cortex-M3 */ |
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| 72 | |||
| 73 | q31_t in1, in2, in3, in4; /* Temporary input variables */ |
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| 74 | |||
| 75 | /*loop Unrolling */ |
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| 76 | blkCnt = blockSize >> 2U; |
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| 77 | |||
| 78 | /* First part of the processing with loop unrolling. Compute 8 outputs at a time. |
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| 79 | ** a second loop below computes the remaining 1 to 7 samples. */ |
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| 80 | while (blkCnt > 0U) |
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| 81 | { |
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| 82 | /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */ |
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| 83 | /* Compute sum of the squares and then store the result in a temporary variable, sum */ |
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| 84 | /* read two samples from source buffer */ |
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| 85 | in1 = pSrc[0]; |
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| 86 | in2 = pSrc[1]; |
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| 87 | |||
| 88 | /* calculate power and accumulate to accumulator */ |
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| 89 | sum += (q63_t) in1 *in1; |
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| 90 | sum += (q63_t) in2 *in2; |
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| 91 | |||
| 92 | /* read two samples from source buffer */ |
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| 93 | in3 = pSrc[2]; |
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| 94 | in4 = pSrc[3]; |
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| 95 | |||
| 96 | /* calculate power and accumulate to accumulator */ |
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| 97 | sum += (q63_t) in3 *in3; |
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| 98 | sum += (q63_t) in4 *in4; |
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| 99 | |||
| 100 | |||
| 101 | /* update source buffer to process next samples */ |
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| 102 | pSrc += 4U; |
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| 103 | |||
| 104 | /* Decrement the loop counter */ |
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| 105 | blkCnt--; |
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| 106 | } |
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| 107 | |||
| 108 | /* If the blockSize is not a multiple of 8, compute any remaining output samples here. |
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| 109 | ** No loop unrolling is used. */ |
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| 110 | blkCnt = blockSize % 0x4U; |
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| 111 | |||
| 112 | #else |
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| 113 | /* Run the below code for Cortex-M0 */ |
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| 114 | |||
| 115 | blkCnt = blockSize; |
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| 116 | |||
| 117 | #endif /* #if defined (ARM_MATH_DSP) */ |
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| 118 | |||
| 119 | while (blkCnt > 0U) |
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| 120 | { |
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| 121 | /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */ |
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| 122 | /* Compute sum of the squares and then store the results in a temporary variable, sum */ |
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| 123 | in = *pSrc++; |
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| 124 | sum += (q63_t) in *in; |
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| 125 | |||
| 126 | /* Decrement the loop counter */ |
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| 127 | blkCnt--; |
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| 128 | } |
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| 129 | |||
| 130 | /* Convert data in 2.62 to 1.31 by 31 right shifts and saturate */ |
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| 131 | /* Compute Rms and store the result in the destination vector */ |
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| 132 | arm_sqrt_q31(clip_q63_to_q31((sum / (q63_t) blockSize) >> 31), pResult); |
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| 133 | } |
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| 134 | |||
| 135 | /** |
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| 136 | * @} end of RMS group |
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| 137 | */ |