hardware/arduino/sam/system/CMSIS/CMSIS/DSP_Lib/Source/StatisticsFunctions/arm_rms_q15.c

/* ----------------------------------------------------------------------   
* Copyright (C) 2010 ARM Limited. All rights reserved.   
*   
* $Date:        15. July 2011  
* $Revision: 	V1.0.10  
*   
* Project: 	    CMSIS DSP Library   
* Title:		arm_rms_q15.c   
*   
* Description:	Root Mean Square of the elements of a Q15 vector. 
*   
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*  
* Version 1.0.10 2011/7/15 
*    Big Endian support added and Merged M0 and M3/M4 Source code.  
*   
* Version 1.0.3 2010/11/29  
*    Re-organized the CMSIS folders and updated documentation.   
*    
* Version 1.0.2 2010/11/11   
*    Documentation updated.    
*   
* Version 1.0.1 2010/10/05    
*    Production release and review comments incorporated.   
*   
* Version 1.0.0 2010/09/20    
*    Production release and review comments incorporated.   
* ---------------------------------------------------------------------------- */

#include "arm_math.h"

/**   
 * @addtogroup RMS   
 * @{   
 */

/**   
 * @brief Root Mean Square of the elements of a Q15 vector.   
 * @param[in]       *pSrc points to the input vector   
 * @param[in]       blockSize length of the input vector   
 * @param[out]      *pResult rms value returned here   
 * @return none.   
 *   
 * @details   
 * <b>Scaling and Overflow Behavior:</b>   
 *   
 * \par   
 * The function is implemented using a 64-bit internal accumulator.   
 * The input is represented in 1.15 format.   
 * Intermediate multiplication yields a 2.30 format, and this   
 * result is added without saturation to a 64-bit accumulator in 34.30 format.   
 * With 33 guard bits in the accumulator, there is no risk of overflow, and the   
 * full precision of the intermediate multiplication is preserved.   
 * Finally, the 34.30 result is truncated to 34.15 format by discarding the lower    
 * 15 bits, and then saturated to yield a result in 1.15 format.   
 *   
 */

void arm_rms_q15(
  q15_t * pSrc,
  uint32_t blockSize,
  q15_t * pResult)
{
  q63_t sum = 0;                                 /* accumulator */

#ifndef ARM_MATH_CM0

  /* Run the below code for Cortex-M4 and Cortex-M3 */

  q31_t in;                                      /* temporary variable to store the input value */
  q15_t in1;                                     /* temporary variable to store the input value */
  uint32_t blkCnt;                               /* loop counter */

  /* loop Unrolling */
  blkCnt = blockSize >> 2u;

  /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.   
   ** a second loop below computes the remaining 1 to 3 samples. */
  while(blkCnt > 0u)
  {
    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    /* Compute sum of the squares and then store the results in a temporary variable, sum */
    in = *__SIMD32(pSrc)++;
    sum = __SMLALD(in, in, sum);
    in = *__SIMD32(pSrc)++;
    sum = __SMLALD(in, in, sum);

    /* Decrement the loop counter */
    blkCnt--;
  }

  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.   
   ** No loop unrolling is used. */
  blkCnt = blockSize % 0x4u;

  while(blkCnt > 0u)
  {
    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    /* Compute sum of the squares and then store the results in a temporary variable, sum */
    in1 = *pSrc++;
    sum = __SMLALD(in1, in1, sum);

    /* Decrement the loop counter */
    blkCnt--;
  }

  /* Truncating and saturating the accumulator to 1.15 format */
  sum = __SSAT((q31_t) (sum >> 15), 16);

  in1 = (q15_t) (sum / blockSize);

  /* Store the result in the destination */
  arm_sqrt_q15(in1, pResult);

#else

  /* Run the below code for Cortex-M0 */

  q15_t in;                                      /* temporary variable to store the input value */
  uint32_t blkCnt;                               /* loop counter */

  /* Loop over blockSize number of values */
  blkCnt = blockSize;

  while(blkCnt > 0u)
  {
    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    /* Compute sum of the squares and then store the results in a temporary variable, sum */
    in = *pSrc++;
    sum += ((q31_t) in * in);

    /* Decrement the loop counter */
    blkCnt--;
  }

  /* Truncating and saturating the accumulator to 1.15 format */
  sum = __SSAT((q31_t) (sum >> 15), 16);

  in = (q15_t) (sum / blockSize);

  /* Store the result in the destination */
  arm_sqrt_q15(in, pResult);

#endif /* #ifndef ARM_MATH_CM0 */

}

/**   
 * @} end of RMS group   
 */