| 1 | /* ----------------------------------------------------------------------
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| 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 |
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| 29 | #include "arm_math.h"
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| 30 |
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| 31 | /**
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| 32 | * @addtogroup RMS
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| 33 | * @{
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| 34 | */
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| 35 |
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| 36 |
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| 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 |
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| 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 |
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| 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 |
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| 73 | q31_t in1, in2, in3, in4; /* Temporary input variables */
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| 74 |
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| 75 | /*loop Unrolling */
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| 76 | blkCnt = blockSize >> 2U;
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| 77 |
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| 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 |
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| 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 |
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| 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 |
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| 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 |
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| 100 |
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| 101 | /* update source buffer to process next samples */
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| 102 | pSrc += 4U;
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| 103 |
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| 104 | /* Decrement the loop counter */
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| 105 | blkCnt--;
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| 106 | }
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| 107 |
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| 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 |
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| 112 | #else
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| 113 | /* Run the below code for Cortex-M0 */
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| 114 |
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| 115 | blkCnt = blockSize;
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| 116 |
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| 117 | #endif /* #if defined (ARM_MATH_DSP) */
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| 118 |
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| 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 |
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| 126 | /* Decrement the loop counter */
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| 127 | blkCnt--;
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| 128 | }
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| 129 |
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| 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 |
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| 135 | /**
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| 136 | * @} end of RMS group
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| 137 | */
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