| 1 | /* ----------------------------------------------------------------------
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| 2 | * Project: CMSIS DSP Library
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| 3 | * Title: arm_mean_q15.c
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| 4 | * Description: Mean value 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 |
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| 29 | #include "arm_math.h"
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| 30 |
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| 31 | /**
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| 32 | * @ingroup groupStats
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| 33 | */
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| 34 |
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| 35 | /**
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| 36 | * @addtogroup mean
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| 37 | * @{
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| 38 | */
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| 39 |
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| 40 |
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| 41 | /**
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| 42 | * @brief Mean value of a Q15 vector.
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| 43 | * @param[in] *pSrc points to the input vector
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| 44 | * @param[in] blockSize length of the input vector
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| 45 | * @param[out] *pResult mean value returned here
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| 46 | * @return none.
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| 47 | *
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| 48 | * @details
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| 49 | * <b>Scaling and Overflow Behavior:</b>
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| 50 | * \par
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| 51 | * The function is implemented using a 32-bit internal accumulator.
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| 52 | * The input is represented in 1.15 format and is accumulated in a 32-bit
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| 53 | * accumulator in 17.15 format.
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| 54 | * There is no risk of internal overflow with this approach, and the
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| 55 | * full precision of intermediate result is preserved.
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| 56 | * Finally, the accumulator is saturated and truncated to yield a result of 1.15 format.
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| 57 | *
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| 58 | */
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| 59 |
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| 60 | void arm_mean_q15(
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| 61 | q15_t * pSrc,
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| 62 | uint32_t blockSize,
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| 63 | q15_t * pResult)
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| 64 | {
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| 65 | q31_t sum = 0; /* Temporary result storage */
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| 66 | uint32_t blkCnt; /* loop counter */
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| 67 |
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| 68 | #if defined (ARM_MATH_DSP)
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| 69 | /* Run the below code for Cortex-M4 and Cortex-M3 */
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| 70 |
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| 71 | q31_t in;
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| 72 |
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| 73 | /*loop Unrolling */
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| 74 | blkCnt = blockSize >> 2U;
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| 75 |
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| 76 | /* First part of the processing with loop unrolling. Compute 4 outputs at a time.
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| 77 | ** a second loop below computes the remaining 1 to 3 samples. */
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| 78 | while (blkCnt > 0U)
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| 79 | {
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| 80 | /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
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| 81 | in = *__SIMD32(pSrc)++;
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| 82 | sum += ((in << 16U) >> 16U);
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| 83 | sum += (in >> 16U);
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| 84 | in = *__SIMD32(pSrc)++;
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| 85 | sum += ((in << 16U) >> 16U);
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| 86 | sum += (in >> 16U);
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| 87 |
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| 88 | /* Decrement the loop counter */
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| 89 | blkCnt--;
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| 90 | }
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| 91 |
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| 92 | /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
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| 93 | ** No loop unrolling is used. */
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| 94 | blkCnt = blockSize % 0x4U;
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| 95 |
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| 96 | #else
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| 97 | /* Run the below code for Cortex-M0 */
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| 98 |
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| 99 | /* Loop over blockSize number of values */
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| 100 | blkCnt = blockSize;
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| 101 |
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| 102 | #endif /* #if defined (ARM_MATH_DSP) */
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| 103 |
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| 104 | while (blkCnt > 0U)
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| 105 | {
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| 106 | /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
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| 107 | sum += *pSrc++;
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| 108 |
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| 109 | /* Decrement the loop counter */
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| 110 | blkCnt--;
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| 111 | }
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| 112 |
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| 113 | /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) / blockSize */
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| 114 | /* Store the result to the destination */
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| 115 | *pResult = (q15_t) (sum / (q31_t)blockSize);
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| 116 | }
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| 117 |
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| 118 | /**
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| 119 | * @} end of mean group
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| 120 | */
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