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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_rms_q15.c    
  9. *    
  10. * Description:  Root Mean Square of the elements 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.  * @addtogroup RMS    
  45.  * @{    
  46.  */
  47.  
  48. /**    
  49.  * @brief Root Mean Square of the elements of a Q15 vector.    
  50.  * @param[in]       *pSrc points to the input vector    
  51.  * @param[in]       blockSize length of the input vector    
  52.  * @param[out]      *pResult rms value returned here    
  53.  * @return none.    
  54.  *    
  55.  * @details    
  56.  * <b>Scaling and Overflow Behavior:</b>    
  57.  *    
  58.  * \par    
  59.  * The function is implemented using a 64-bit internal accumulator.    
  60.  * The input is represented in 1.15 format.    
  61.  * Intermediate multiplication yields a 2.30 format, and this    
  62.  * result is added without saturation to a 64-bit accumulator in 34.30 format.    
  63.  * With 33 guard bits in the accumulator, there is no risk of overflow, and the    
  64.  * full precision of the intermediate multiplication is preserved.    
  65.  * Finally, the 34.30 result is truncated to 34.15 format by discarding the lower    
  66.  * 15 bits, and then saturated to yield a result in 1.15 format.    
  67.  *    
  68.  */
  69.  
  70. void arm_rms_q15(
  71.   q15_t * pSrc,
  72.   uint32_t blockSize,
  73.   q15_t * pResult)
  74. {
  75.   q63_t sum = 0;                                 /* accumulator */
  76.  
  77. #ifndef ARM_MATH_CM0_FAMILY
  78.  
  79.   /* Run the below code for Cortex-M4 and Cortex-M3 */
  80.  
  81.   q31_t in;                                      /* temporary variable to store the input value */
  82.   q15_t in1;                                     /* temporary variable to store the input value */
  83.   uint32_t blkCnt;                               /* loop counter */
  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[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
  93.     /* Compute sum of the squares and then store the results in a temporary variable, sum */
  94.     in = *__SIMD32(pSrc)++;
  95.     sum = __SMLALD(in, in, sum);
  96.     in = *__SIMD32(pSrc)++;
  97.     sum = __SMLALD(in, in, sum);
  98.  
  99.     /* Decrement the loop counter */
  100.     blkCnt--;
  101.   }
  102.  
  103.   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.    
  104.    ** No loop unrolling is used. */
  105.   blkCnt = blockSize % 0x4u;
  106.  
  107.   while(blkCnt > 0u)
  108.   {
  109.     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
  110.     /* Compute sum of the squares and then store the results in a temporary variable, sum */
  111.     in1 = *pSrc++;
  112.     sum = __SMLALD(in1, in1, sum);
  113.  
  114.     /* Decrement the loop counter */
  115.     blkCnt--;
  116.   }
  117.  
  118.   /* Truncating and saturating the accumulator to 1.15 format */
  119.   /* Store the result in the destination */
  120.   arm_sqrt_q15(__SSAT((sum / (q63_t)blockSize) >> 15, 16), pResult);
  121.  
  122. #else
  123.  
  124.   /* Run the below code for Cortex-M0 */
  125.  
  126.   q15_t in;                                      /* temporary variable to store the input value */
  127.   uint32_t blkCnt;                               /* loop counter */
  128.  
  129.   /* Loop over blockSize number of values */
  130.   blkCnt = blockSize;
  131.  
  132.   while(blkCnt > 0u)
  133.   {
  134.     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
  135.     /* Compute sum of the squares and then store the results in a temporary variable, sum */
  136.     in = *pSrc++;
  137.     sum += ((q31_t) in * in);
  138.  
  139.     /* Decrement the loop counter */
  140.     blkCnt--;
  141.   }
  142.  
  143.   /* Truncating and saturating the accumulator to 1.15 format */
  144.   /* Store the result in the destination */
  145.   arm_sqrt_q15(__SSAT((sum / (q63_t)blockSize) >> 15, 16), pResult);
  146.  
  147. #endif /* #ifndef ARM_MATH_CM0_FAMILY */
  148.  
  149. }
  150.  
  151. /**    
  152.  * @} end of RMS group    
  153.  */
  154.