/* ----------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date: 16/10/14 6:01p $Revision:  V.1.4.5
*
* Project:      CMSIS DSP Library
* Title:        arm_rms_q31.c
*
* Description:  Root Mean Square of the elements of a Q31 vector.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in
*     the documentation and/or other materials provided with the
*     distribution.
*   - Neither the name of ARM LIMITED nor the names of its contributors
*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* ---------------------------------------------------------------------------- */

#include "arm_math.h"

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


/**
 * @brief Root Mean Square of the elements of a Q31 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 an internal 64-bit accumulator.
 * The input is represented in 1.31 format, and intermediate multiplication
 * yields a 2.62 format.
 * The accumulator maintains full precision of the intermediate multiplication results,
 * but provides only a single guard bit.
 * There is no saturation on intermediate additions.
 * If the accumulator overflows, it wraps around and distorts the result.
 * In order to avoid overflows completely, the input signal must be scaled down by
 * log2(blockSize) bits, as a total of blockSize additions are performed internally.
 * Finally, the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value.
 *
 */

void arm_rms_q31(
    q31_t * pSrc,
    uint32_t blockSize,
    q31_t * pResult)
{
    q63_t sum = 0;                                 /* accumulator */
    q31_t in;                                      /* Temporary variable to store the input */
    uint32_t blkCnt;                               /* loop counter */

#ifndef ARM_MATH_CM0_FAMILY

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

    q31_t in1, in2, in3, in4;                      /* Temporary input variables */

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

    /* First part of the processing with loop unrolling.  Compute 8 outputs at a time.
     ** a second loop below computes the remaining 1 to 7 samples. */
    while(blkCnt > 0u)
    {
        /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
        /* Compute sum of the squares and then store the result in a temporary variable, sum */
        /* read two samples from source buffer */
        in1 = pSrc[0];
        in2 = pSrc[1];

        /* calculate power and accumulate to accumulator */
        sum += (q63_t) in1 * in1;
        sum += (q63_t) in2 * in2;

        /* read two samples from source buffer */
        in3 = pSrc[2];
        in4 = pSrc[3];

        /* calculate power and accumulate to accumulator */
        sum += (q63_t) in3 * in3;
        sum += (q63_t) in4 * in4;


        /* update source buffer to process next samples */
        pSrc += 4u;

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

    /* If the blockSize is not a multiple of 8, compute any remaining output samples here.
     ** No loop unrolling is used. */
    blkCnt = blockSize % 0x4u;

#else

    /* Run the below code for Cortex-M0 */
    blkCnt = blockSize;

#endif /* #ifndef ARM_MATH_CM0_FAMILY */

    while(blkCnt > 0u)
    {
        /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
        /* Compute sum of the squares and then store the results in a temporary variable, sum */
        in = *pSrc++;
        sum += (q63_t) in * in;

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

    /* Convert data in 2.62 to 1.31 by 31 right shifts and saturate */
    /* Compute Rms and store the result in the destination vector */
    arm_sqrt_q31(clip_q63_to_q31((sum / (q63_t) blockSize) >> 31), pResult);
}

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