ti/dsplib/src/DSP_autocor/c66/DSP_autocor_cn.c

   1 /* ======================================================================= */
   2 /*  NAME                                                                   */
   3 /*      DSP_autocor_cn -- Autocorrelation                                  */
   4 /*                                                                         */
   5 /*   USAGE                                                                 */
   6 /*        This routine has the following C prototype:                      */
   7 /*                                                                         */
   8 /*        void DSP_autocor_cn (                                            */
   9 /*            short *restrict r,                                           */
  10 /*            const short *restrict x,                                     */
  11 /*            int          nx,                                             */
  12 /*            int          nr                                              */
  13 /*         );                                                              */
  14 /*                                                                         */
  15 /*        r[nr]   : Output array                                           */
  16 /*        x[nr+nx]: Input array. The first nr elements are assumed to be 0 */
  17 /*        nx      : Length of autocorrelation                              */
  18 /*        nr      : Number of lags                                         */
  19 /*                                                                         */
  20 /*                                                                         */
  21 /*     DESCRIPTION                                                         */
  22 /*        This routine performs an autocorrelation of an input vector      */
  23 /*        x. The length of the autocorrelation is nx samples. Since nr     */
  24 /*        such autocorrelations are performed, input vector x needs to be  */
  25 /*        of length nx + nr. This produces nr output results which are     */
  26 /*        stored in an output array r.                                     */
  27 /*                                                                         */
  28 /*        The following diagram illustrates how the correlations are       */
  29 /*        obtained.                                                        */
  30 /*                                                                         */
  31 /*        Example for nr=8, nx=24:                                         */
  32 /*        0       nr                  nx+nr-1                              */
  33 /*        |-------|----------------------|  <- x[]                         */
  34 /*        |       |----------------------|  -> r[0]                        */
  35 /*        |      |----------------------|   -> r[1]                        */
  36 /*        |     |----------------------|    -> r[2]                        */
  37 /*        |    |----------------------|     -> r[3]                        */
  38 /*        |   |----------------------|      -> r[4]                        */
  39 /*        |  |----------------------|       -> r[5]                        */
  40 /*        | |----------------------|        -> r[6]                        */
  41 /*                                                                         */
  42 /*        Note that x[0] is never used, but is required for padding to     */
  43 /*        make x[nr] double-word aligned.                                  */
  44 /*                                                                         */
  45 /*   ASSUMPTIONS                                                           */
  46 /*        The first nr elements are assumed to be 0.                       */
  47 /*                                                                         */
  48 /* Copyright (C) 2011 Texas Instruments Incorporated - http://www.ti.com/  */
  49 /*                                                                         */
  50 /*                                                                         */
  51 /*  Redistribution and use in source and binary forms, with or without     */
  52 /*  modification, are permitted provided that the following conditions     */
  53 /*  are met:                                                               */
  54 /*                                                                         */
  55 /*    Redistributions of source code must retain the above copyright       */
  56 /*    notice, this list of conditions and the following disclaimer.        */
  57 /*                                                                         */
  58 /*    Redistributions in binary form must reproduce the above copyright    */
  59 /*    notice, this list of conditions and the following disclaimer in the  */
  60 /*    documentation and/or other materials provided with the               */
  61 /*    distribution.                                                        */
  62 /*                                                                         */
  63 /*    Neither the name of Texas Instruments Incorporated nor the names of  */
  64 /*    its contributors may be used to endorse or promote products derived  */
  65 /*    from this software without specific prior written permission.        */
  66 /*                                                                         */
  67 /*  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS    */
  68 /*  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT      */
  69 /*  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR  */
  70 /*  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT   */
  71 /*  OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,  */
  72 /*  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT       */
  73 /*  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,  */
  74 /*  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY  */
  75 /*  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT    */
  76 /*  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE  */
  77 /*  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.   */
  78 /*                                                                         */
  79 /* ======================================================================= */
  80
  81 #pragma CODE_SECTION(DSP_autocor_cn, ".text:ansi");
  82
  83 #include "DSP_autocor_cn.h"
  84
  85 void DSP_autocor_cn (
  86     short *restrict r,
  87     const short *restrict x,
  88     int nx,
  89     int nr
  90 )
  91 {
  92    int i, k;
  93    int sum;
  94
  95    #ifndef NOASSUME
  96    _nassert (nr % 4 == 0);
  97    #endif
  98
  99    /*----------------------------------------------------------------------*/
 100    /* Outer loop that iterates for every output. There are 'nr' output     */
 101    /* samples to be computed. Hence this loop iterates 'nr' times. 'nr'    */
 102    /* needs to be a multiple of 4. This information is conveyed to the     */
 103    /* compiler.                                                            */
 104    /*----------------------------------------------------------------------*/
 105    for (i = 0; i < nr; i++) {
 106       sum = 0;
 107
 108       #ifndef NOASSUME
 109       _nassert(nx % 8 == 0);
 110       _nassert((int)(x) % 8 == 0);
 111       _nassert((int)(r) % 4 == 0);
 112       _nassert(nr % 4 == 0);
 113       #pragma MUST_ITERATE(8,,4);
 114       #endif
 115
 116       /*-------------------------------------------------------------------*/
 117       /*  Compute one autocorrelation. Each autocorrelation has 'nx' terms */
 118       /*  'nx' is assumed to be a multiple of 8.                           */
 119       /*-------------------------------------------------------------------*/
 120       for (k = nr; k < nx + nr; k++)
 121           sum += x[k] * x[k-i];
 122
 123       /*-------------------------------------------------------------------*/
 124       /* Shift out autocorrelation sum taking into account Q15 math.       */
 125       /*-------------------------------------------------------------------*/
 126       r[i] = sum  >> 15;
 127    }
 128 }
 129
 130 /* ======================================================================== */
 131 /*  End of file:  DSP_autocor_cn.c                                          */
 132 /* ------------------------------------------------------------------------ */
 133 /*            Copyright (c) 2011 Texas Instruments, Incorporated.           */
 134 /*                           All Rights Reserved.                           */
 135 /* ======================================================================== */
 136