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# arm_rms_q31.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_q31.c
    00009 *
    00010 * Description:  root mean square value of an array of Q31 type
    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
    00059 void arm_rms_q31(
    00060   q31_t * pSrc,
    00061   uint32_t blockSize,
    00062   q31_t * pResult)
    00063 {
    00064   q31_t *pIn1 = pSrc;                            /* SrcA pointer */
    00065   q63_t sum = 0;                                 /* accumulator */
    00066   q31_t in;                                      /* Temporary variable to store the input */
    00067   uint32_t blkCnt;                               /* loop counter */
    00068
    00069   /*loop Unrolling */
    00070   blkCnt = blockSize >> 2u;
    00071
    00072   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00073    ** a second loop below computes the remaining 1 to 3 samples. */
    00074   while(blkCnt > 0u)
    00075   {
    00076     /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
    00077     /* Compute sum of the squares and then store the result in a temporary variable, sum */
    00078     in = *pIn1++;
    00079     sum += (q63_t) in *in;
    00080     in = *pIn1++;
    00081     sum += (q63_t) in *in;
    00082     in = *pIn1++;
    00083     sum += (q63_t) in *in;
    00084     in = *pIn1++;
    00085     sum += (q63_t) in *in;
    00086
    00087     /* Decrement the loop counter */
    00088     blkCnt--;
    00089   }
    00090
    00091   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00092    ** No loop unrolling is used. */
    00093   blkCnt = blockSize % 0x4u;
    00094
    00095   while(blkCnt > 0u)
    00096   {
    00097     /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
    00098     /* Compute sum of the squares and then store the results in a temporary variable, sum */
    00099     in = *pIn1++;
    00100     sum += (q63_t) in *in;
    00101
    00102     /* Decrement the loop counter */
    00103     blkCnt--;
    00104   }
    00105
    00106   /* Convert data in 2.62 to 1.31 by 31 right shifts */
    00107   sum = sum >> 31;
    00108
    00109   /* Compute Rms and store the result in the destination vector */
    00110   arm_sqrt_q31((q31_t) (sum / (int32_t) blockSize), pResult);
    00111 }
    00112

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