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  1. /* ----------------------------------------------------------------------    
  2. * Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
  3. *    
  4. * $Date:        19. March 2015
  5. * $Revision:    V.1.4.5  
  6. *    
  7. * Project:          CMSIS DSP Library    
  8. * Title:                arm_mean_q15.c    
  9. *    
  10. * Description:  Mean value of a Q15 vector.  
  11. *    
  12. * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
  13. *  
  14. * Redistribution and use in source and binary forms, with or without
  15. * modification, are permitted provided that the following conditions
  16. * are met:
  17. *   - Redistributions of source code must retain the above copyright
  18. *     notice, this list of conditions and the following disclaimer.
  19. *   - Redistributions in binary form must reproduce the above copyright
  20. *     notice, this list of conditions and the following disclaimer in
  21. *     the documentation and/or other materials provided with the
  22. *     distribution.
  23. *   - Neither the name of ARM LIMITED nor the names of its contributors
  24. *     may be used to endorse or promote products derived from this
  25. *     software without specific prior written permission.
  26. *
  27. * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  28. * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  29. * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  30. * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  31. * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  32. * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  33. * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  34. * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  35. * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36. * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  37. * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  38. * POSSIBILITY OF SUCH DAMAGE.  
  39. * -------------------------------------------------------------------- */
  40.  
  41. #include "arm_math.h"
  42.  
  43. /**    
  44.  * @ingroup groupStats    
  45.  */
  46.  
  47. /**    
  48.  * @addtogroup mean    
  49.  * @{    
  50.  */
  51.  
  52. /**    
  53.  * @brief Mean value of a Q15 vector.    
  54.  * @param[in]       *pSrc points to the input vector    
  55.  * @param[in]       blockSize length of the input vector    
  56.  * @param[out]      *pResult mean value returned here    
  57.  * @return none.    
  58.  *    
  59.  * @details    
  60.  * <b>Scaling and Overflow Behavior:</b>    
  61.  * \par    
  62.  * The function is implemented using a 32-bit internal accumulator.    
  63.  * The input is represented in 1.15 format and is accumulated in a 32-bit    
  64.  * accumulator in 17.15 format.    
  65.  * There is no risk of internal overflow with this approach, and the    
  66.  * full precision of intermediate result is preserved.    
  67.  * Finally, the accumulator is saturated and truncated to yield a result of 1.15 format.    
  68.  *    
  69.  */
  70.  
  71.  
  72. void arm_mean_q15(
  73.   q15_t * pSrc,
  74.   uint32_t blockSize,
  75.   q15_t * pResult)
  76. {
  77.   q31_t sum = 0;                                 /* Temporary result storage */
  78.   uint32_t blkCnt;                               /* loop counter */
  79.  
  80. #ifndef ARM_MATH_CM0_FAMILY
  81.  
  82.   /* Run the below code for Cortex-M4 and Cortex-M3 */
  83.   q31_t in;
  84.  
  85.   /*loop Unrolling */
  86.   blkCnt = blockSize >> 2u;
  87.  
  88.   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.    
  89.    ** a second loop below computes the remaining 1 to 3 samples. */
  90.   while(blkCnt > 0u)
  91.   {
  92.     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
  93.     in = *__SIMD32(pSrc)++;
  94.     sum += ((in << 16) >> 16);
  95.     sum += (in >> 16);
  96.     in = *__SIMD32(pSrc)++;
  97.     sum += ((in << 16) >> 16);
  98.     sum += (in >> 16);
  99.  
  100.     /* Decrement the loop counter */
  101.     blkCnt--;
  102.   }
  103.  
  104.   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.    
  105.    ** No loop unrolling is used. */
  106.   blkCnt = blockSize % 0x4u;
  107.  
  108. #else
  109.  
  110.   /* Run the below code for Cortex-M0 */
  111.  
  112.   /* Loop over blockSize number of values */
  113.   blkCnt = blockSize;
  114.  
  115. #endif /* #ifndef ARM_MATH_CM0_FAMILY */
  116.  
  117.   while(blkCnt > 0u)
  118.   {
  119.     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
  120.     sum += *pSrc++;
  121.  
  122.     /* Decrement the loop counter */
  123.     blkCnt--;
  124.   }
  125.  
  126.   /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) / blockSize  */
  127.   /* Store the result to the destination */
  128.   *pResult = (q15_t) (sum / (q31_t)blockSize);
  129. }
  130.  
  131. /**    
  132.  * @} end of mean group    
  133.  */
  134.