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# arm_rms_q15.c

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    00001 /* ----------------------------------------------------------------------
    00002 * Copyright (C) 2010 ARM Limited. All rights reserved.
    00003 *
    00004 * $Date:        29. November 2010
    00005 * $Revision:    V1.0.3
    00006 *
    00007 * Project:      CMSIS DSP Library
    00008 * Title:        arm_rms_q15.c
    00009 *
    00010 * Description:  Processing function for the Q15 RMS
    00011 *
    00012 * Target Processor: Cortex-M4/Cortex-M3
    00013 *
    00014 * Version 1.0.3 2010/11/29
    00015 *    Re-organized the CMSIS folders and updated documentation.
    00016 *
    00017 * Version 1.0.2 2010/11/11
    00018 *    Documentation updated.
    00019 *
    00020 * Version 1.0.1 2010/10/05
    00021 *    Production release and review comments incorporated.
    00022 *
    00023 * Version 1.0.0 2010/09/20
    00024 *    Production release and review comments incorporated.
    00025 * ---------------------------------------------------------------------------- */
    00026
    00027 #include "arm_math.h"
    00028
    00056 void arm_rms_q15(
    00057   q15_t * pSrc,
    00058   uint32_t blockSize,
    00059   q15_t * pResult)
    00060 {
    00061   q63_t sum = 0;                                 /* accumulator */
    00062   q31_t in;                                      /* temporary variable to store the input value */
    00063   q15_t in1;                                     /* temporary variable to store the input value */
    00064   uint32_t blkCnt;                               /* loop counter */
    00065
    00066   /* loop Unrolling */
    00067   blkCnt = blockSize >> 2u;
    00068
    00069   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00070    ** a second loop below computes the remaining 1 to 3 samples. */
    00071   while(blkCnt > 0u)
    00072   {
    00073     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00074     /* Compute sum of the squares and then store the results in a temporary variable, sum */
    00075     in = *__SIMD32(pSrc)++;
    00076     sum = __SMLALD(in, in, sum);
    00077     in = *__SIMD32(pSrc)++;
    00078     sum = __SMLALD(in, in, sum);
    00079
    00080     /* Decrement the loop counter */
    00081     blkCnt--;
    00082   }
    00083
    00084   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00085    ** No loop unrolling is used. */
    00086   blkCnt = blockSize % 0x4u;
    00087
    00088   while(blkCnt > 0u)
    00089   {
    00090     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00091     /* Compute sum of the squares and then store the results in a temporary variable, sum */
    00092     in1 = *pSrc++;
    00093     sum = __SMLALD(in1, in1, sum);
    00094
    00095     /* Decrement the loop counter */
    00096     blkCnt--;
    00097   }
    00098
    00099   /* Truncating and saturating the accumulator to 1.15 format */
    00100   sum = __SSAT((q31_t) (sum >> 15), 16);
    00101
    00102   in1 = (q15_t) (sum / blockSize);
    00103
    00104   /* Store the result in the destination */
    00105   arm_sqrt_q15(in1, pResult);
    00106 }
    00107

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