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  1. /* ----------------------------------------------------------------------
  2.  * Project:      CMSIS DSP Library
  3.  * Title:        arm_power_q7.c
  4.  * Description:  Sum of the squares of the elements 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 power
  37.  * @{
  38.  */
  39.  
  40. /**
  41.  * @brief Sum of the squares of the elements of a Q7 vector.
  42.  * @param[in]       *pSrc points to the input vector
  43.  * @param[in]       blockSize length of the input vector
  44.  * @param[out]      *pResult sum of the squares value returned here
  45.  * @return none.
  46.  *
  47.  * @details
  48.  * <b>Scaling and Overflow Behavior:</b>
  49.  *
  50.  * \par
  51.  * The function is implemented using a 32-bit internal accumulator.
  52.  * The input is represented in 1.7 format.
  53.  * Intermediate multiplication yields a 2.14 format, and this
  54.  * result is added without saturation to an accumulator in 18.14 format.
  55.  * With 17 guard bits in the accumulator, there is no risk of overflow, and the
  56.  * full precision of the intermediate multiplication is preserved.
  57.  * Finally, the return result is in 18.14 format.
  58.  *
  59.  */
  60.  
  61. void arm_power_q7(
  62.   q7_t * pSrc,
  63.   uint32_t blockSize,
  64.   q31_t * pResult)
  65. {
  66.   q31_t sum = 0;                                 /* Temporary result storage */
  67.   q7_t in;                                       /* Temporary variable to store input */
  68.   uint32_t blkCnt;                               /* loop counter */
  69.  
  70. #if defined (ARM_MATH_DSP)
  71.   /* Run the below code for Cortex-M4 and Cortex-M3 */
  72.  
  73.   q31_t input1;                                  /* Temporary variable to store packed input */
  74.   q31_t in1, in2;                                /* Temporary variables to store input */
  75.  
  76.   /*loop Unrolling */
  77.   blkCnt = blockSize >> 2U;
  78.  
  79.   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
  80.    ** a second loop below computes the remaining 1 to 3 samples. */
  81.   while (blkCnt > 0U)
  82.   {
  83.     /* Reading two inputs of pSrc vector and packing */
  84.     input1 = *__SIMD32(pSrc)++;
  85.  
  86.     in1 = __SXTB16(__ROR(input1, 8));
  87.     in2 = __SXTB16(input1);
  88.  
  89.     /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
  90.     /* calculate power and accumulate to accumulator */
  91.     sum = __SMLAD(in1, in1, sum);
  92.     sum = __SMLAD(in2, in2, sum);
  93.  
  94.     /* Decrement the loop counter */
  95.     blkCnt--;
  96.   }
  97.  
  98.   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
  99.    ** No loop unrolling is used. */
  100.   blkCnt = blockSize % 0x4U;
  101.  
  102. #else
  103.   /* Run the below code for Cortex-M0 */
  104.  
  105.   /* Loop over blockSize number of values */
  106.   blkCnt = blockSize;
  107.  
  108. #endif /* #if defined (ARM_MATH_DSP) */
  109.  
  110.   while (blkCnt > 0U)
  111.   {
  112.     /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
  113.     /* Compute Power and then store the result in a temporary variable, sum. */
  114.     in = *pSrc++;
  115.     sum += ((q15_t) in * in);
  116.  
  117.     /* Decrement the loop counter */
  118.     blkCnt--;
  119.   }
  120.  
  121.   /* Store the result in 18.14 format  */
  122.   *pResult = sum;
  123. }
  124.  
  125. /**
  126.  * @} end of power group
  127.  */
  128.