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  1. /* ----------------------------------------------------------------------
  2.  * Project:      CMSIS DSP Library
  3.  * Title:        arm_mean_q7.c
  4.  * Description:  Mean value of a Q7 vector
  5.  *
  6.  * $Date:        27. January 2017
  7.  * $Revision:    V.1.5.1
  8.  *
  9.  * Target Processor: Cortex-M cores
  10.  * -------------------------------------------------------------------- */
  11. /*
  12.  * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
  13.  *
  14.  * SPDX-License-Identifier: Apache-2.0
  15.  *
  16.  * Licensed under the Apache License, Version 2.0 (the License); you may
  17.  * not use this file except in compliance with the License.
  18.  * You may obtain a copy of the License at
  19.  *
  20.  * www.apache.org/licenses/LICENSE-2.0
  21.  *
  22.  * Unless required by applicable law or agreed to in writing, software
  23.  * distributed under the License is distributed on an AS IS BASIS, WITHOUT
  24.  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  25.  * See the License for the specific language governing permissions and
  26.  * limitations under the License.
  27.  */
  28.  
  29. #include "arm_math.h"
  30.  
  31. /**
  32.  * @ingroup groupStats
  33.  */
  34.  
  35. /**
  36.  * @addtogroup mean
  37.  * @{
  38.  */
  39.  
  40.  
  41. /**
  42.  * @brief Mean value of a Q7 vector.
  43.  * @param[in]       *pSrc points to the input vector
  44.  * @param[in]       blockSize length of the input vector
  45.  * @param[out]      *pResult mean value returned here
  46.  * @return none.
  47.  *
  48.  * @details
  49.  * <b>Scaling and Overflow Behavior:</b>
  50.  * \par
  51.  * The function is implemented using a 32-bit internal accumulator.
  52.  * The input is represented in 1.7 format and is accumulated in a 32-bit
  53.  * accumulator in 25.7 format.
  54.  * There is no risk of internal overflow with this approach, and the
  55.  * full precision of intermediate result is preserved.
  56.  * Finally, the accumulator is truncated to yield a result of 1.7 format.
  57.  *
  58.  */
  59.  
  60. void arm_mean_q7(
  61.   q7_t * pSrc,
  62.   uint32_t blockSize,
  63.   q7_t * pResult)
  64. {
  65.   q31_t sum = 0;                                 /* Temporary result storage */
  66.   uint32_t blkCnt;                               /* loop counter */
  67.  
  68. #if defined (ARM_MATH_DSP)
  69.   /* Run the below code for Cortex-M4 and Cortex-M3 */
  70.  
  71.   q31_t in;
  72.  
  73.   /*loop Unrolling */
  74.   blkCnt = blockSize >> 2U;
  75.  
  76.   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
  77.    ** a second loop below computes the remaining 1 to 3 samples. */
  78.   while (blkCnt > 0U)
  79.   {
  80.     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
  81.     in = *__SIMD32(pSrc)++;
  82.  
  83.     sum += ((in << 24U) >> 24U);
  84.     sum += ((in << 16U) >> 24U);
  85.     sum += ((in <<  8U) >> 24U);
  86.     sum +=  (in >> 24U);
  87.  
  88.     /* Decrement the loop counter */
  89.     blkCnt--;
  90.   }
  91.  
  92.   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
  93.    ** No loop unrolling is used. */
  94.   blkCnt = blockSize % 0x4U;
  95.  
  96. #else
  97.   /* Run the below code for Cortex-M0 */
  98.  
  99.   /* Loop over blockSize number of values */
  100.   blkCnt = blockSize;
  101.  
  102. #endif /* #if defined (ARM_MATH_DSP) */
  103.  
  104.   while (blkCnt > 0U)
  105.   {
  106.     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
  107.     sum += *pSrc++;
  108.  
  109.     /* Decrement the loop counter */
  110.     blkCnt--;
  111.   }
  112.  
  113.   /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) / blockSize  */
  114.   /* Store the result to the destination */
  115.   *pResult = (q7_t) (sum / (int32_t) blockSize);
  116. }
  117.  
  118. /**
  119.  * @} end of mean group
  120.  */
  121.