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| 56 | mjames | 1 | /* ---------------------------------------------------------------------- |
| 2 | * Project: CMSIS DSP Library |
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| 3 | * Title: arm_rms_q15.c |
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| 4 | * Description: Root Mean Square of the elements of a Q15 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 | /** |
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| 37 | * @brief Root Mean Square of the elements of a Q15 vector. |
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| 38 | * @param[in] *pSrc points to the input vector |
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| 39 | * @param[in] blockSize length of the input vector |
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| 40 | * @param[out] *pResult rms value returned here |
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| 41 | * @return none. |
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| 42 | * |
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| 43 | * @details |
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| 44 | * <b>Scaling and Overflow Behavior:</b> |
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| 45 | * |
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| 46 | * \par |
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| 47 | * The function is implemented using a 64-bit internal accumulator. |
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| 48 | * The input is represented in 1.15 format. |
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| 49 | * Intermediate multiplication yields a 2.30 format, and this |
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| 50 | * result is added without saturation to a 64-bit accumulator in 34.30 format. |
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| 51 | * With 33 guard bits in the accumulator, there is no risk of overflow, and the |
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| 52 | * full precision of the intermediate multiplication is preserved. |
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| 53 | * Finally, the 34.30 result is truncated to 34.15 format by discarding the lower |
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| 54 | * 15 bits, and then saturated to yield a result in 1.15 format. |
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| 55 | * |
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| 56 | */ |
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| 57 | |||
| 58 | void arm_rms_q15( |
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| 59 | q15_t * pSrc, |
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| 60 | uint32_t blockSize, |
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| 61 | q15_t * pResult) |
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| 62 | { |
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| 63 | q63_t sum = 0; /* accumulator */ |
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| 64 | |||
| 65 | #if defined (ARM_MATH_DSP) |
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| 66 | /* Run the below code for Cortex-M4 and Cortex-M3 */ |
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| 67 | |||
| 68 | q31_t in; /* temporary variable to store the input value */ |
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| 69 | q15_t in1; /* temporary variable to store the input value */ |
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| 70 | uint32_t blkCnt; /* loop counter */ |
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| 71 | |||
| 72 | /* loop Unrolling */ |
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| 73 | blkCnt = blockSize >> 2U; |
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| 74 | |||
| 75 | /* First part of the processing with loop unrolling. Compute 4 outputs at a time. |
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| 76 | ** a second loop below computes the remaining 1 to 3 samples. */ |
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| 77 | while (blkCnt > 0U) |
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| 78 | { |
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| 79 | /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ |
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| 80 | /* Compute sum of the squares and then store the results in a temporary variable, sum */ |
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| 81 | in = *__SIMD32(pSrc)++; |
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| 82 | sum = __SMLALD(in, in, sum); |
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| 83 | in = *__SIMD32(pSrc)++; |
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| 84 | sum = __SMLALD(in, in, sum); |
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| 85 | |||
| 86 | /* Decrement the loop counter */ |
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| 87 | blkCnt--; |
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| 88 | } |
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| 89 | |||
| 90 | /* If the blockSize is not a multiple of 4, compute any remaining output samples here. |
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| 91 | ** No loop unrolling is used. */ |
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| 92 | blkCnt = blockSize % 0x4U; |
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| 93 | |||
| 94 | while (blkCnt > 0U) |
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| 95 | { |
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| 96 | /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ |
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| 97 | /* Compute sum of the squares and then store the results in a temporary variable, sum */ |
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| 98 | in1 = *pSrc++; |
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| 99 | sum = __SMLALD(in1, in1, sum); |
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| 100 | |||
| 101 | /* Decrement the loop counter */ |
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| 102 | blkCnt--; |
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| 103 | } |
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| 104 | |||
| 105 | /* Truncating and saturating the accumulator to 1.15 format */ |
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| 106 | /* Store the result in the destination */ |
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| 107 | arm_sqrt_q15(__SSAT((sum / (q63_t)blockSize) >> 15, 16), pResult); |
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| 108 | |||
| 109 | #else |
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| 110 | /* Run the below code for Cortex-M0 */ |
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| 111 | |||
| 112 | q15_t in; /* temporary variable to store the input value */ |
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| 113 | uint32_t blkCnt; /* loop counter */ |
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| 114 | |||
| 115 | /* Loop over blockSize number of values */ |
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| 116 | blkCnt = blockSize; |
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| 117 | |||
| 118 | while (blkCnt > 0U) |
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| 119 | { |
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| 120 | /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ |
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| 121 | /* Compute sum of the squares and then store the results in a temporary variable, sum */ |
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| 122 | in = *pSrc++; |
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| 123 | sum += ((q31_t) in * in); |
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| 124 | |||
| 125 | /* Decrement the loop counter */ |
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| 126 | blkCnt--; |
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| 127 | } |
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| 128 | |||
| 129 | /* Truncating and saturating the accumulator to 1.15 format */ |
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| 130 | /* Store the result in the destination */ |
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| 131 | arm_sqrt_q15(__SSAT((sum / (q63_t)blockSize) >> 15, 16), pResult); |
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| 132 | |||
| 133 | #endif /* #if defined (ARM_MATH_DSP) */ |
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| 134 | |||
| 135 | } |
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| 136 | |||
| 137 | /** |
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| 138 | * @} end of RMS group |
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| 139 | */ |