dsp_maxidx_c.c

来自「dm642函数库」· C语言 代码 · 共 137 行

/* ======================================================================== */
/*  TEXAS INSTRUMENTS, INC.                                                 */
/*                                                                          */
/*  DSPLIB  DSP Signal Processing Library                                   */
/*                                                                          */
/*  This library contains proprietary intellectual property of Texas        */
/*  Instruments, Inc.  The library and its source code are protected by     */
/*  various copyrights, and portions may also be protected by patents or    */
/*  other legal protections.                                                */
/*                                                                          */
/*  This software is licensed for use with Texas Instruments TMS320         */
/*  family DSPs.  This license was provided to you prior to installing      */
/*  the software.  You may review this license by consulting the file       */
/*  TI_license.PDF which accompanies the files in this library.             */
/* ------------------------------------------------------------------------ */
/*          Copyright (C) 2003 Texas Instruments, Incorporated.             */
/*                          All Rights Reserved.                            */
/* ======================================================================== */


/* ======================================================================== */
/*  TEXAS INSTRUMENTS, INC.                                                 */
/*                                                                          */
/*  NAME                                                                    */
/*      DSP_maxidx                                                          */
/*                                                                          */
/*  REVISION DATE                                                           */
/*      13-Aug-2001                                                         */
/*                                                                          */
/*  USAGE                                                                   */
/*      This routine is C-callable and can be called as:                    */
/*                                                                          */
/*          int DSP_maxidx                                                  */
/*          (                                                               */
/*              const short *Input,      // Input array     //              */
/*              short        nInputs     // Length of input //              */
/*          );                                                              */
/*                                                                          */
/*  DESCRIPTION                                                             */
/*      The "DSP_maxidx" routine finds the largest element in an array,     */
/*      returning the index to that element within the array.               */
/*                                                                          */
/*      The input array is treated as 16 separate "columns" that are        */
/*      interleaved throughout the array.  If values in different columns   */
/*      are equal to the maximum value, then the element in the leftmost    */
/*      column is returned.  If two values within a column are equal to     */
/*      the maximum, then the one with the lower index is returned.         */
/*      Column takes precedence over index within the column.               */
/*                                                                          */
/*      The function returns the index of the maximum value.                */
/*                                                                          */
/*  ASSUMPTIONS                                                             */
/*      The input must be at least 48 elements long, and be a multiple      */
/*      of 16 elements long.                                                */
/*                                                                          */
/*      The code requires at least 48 bytes of stack, to make room for a    */
/*      32-byte temporary working buffer.                                   */
/*                                                                          */
/*      The optimized implementations assume that the Input array is        */
/*      double-word aligned, and are optimized for LITTLE ENDIAN.           */
/*                                                                          */
/* ------------------------------------------------------------------------ */
/*            Copyright (c) 2003 Texas Instruments, Incorporated.           */
/*                           All Rights Reserved.                           */
/* ======================================================================== */

int  DSP_maxidx_c
(
    const short *Input,
    int          nInputs
)
{
    int    i, j;
    int    maxLocation, maxIndex;
    short  maxValue;
    short  Max[16];

    #ifndef NOASSUME
    _nassert((int) nInputs      >= 32);
    _nassert((int) nInputs % 16 == 0);
    _nassert((int) Input   % 8  == 0);
    #endif

    /* -------------------------------------------------------------------- */
    /*  Initialize our "max" values from the input array.                   */
    /* -------------------------------------------------------------------- */
    for (i = 0; i < 16; i++)
        Max[i] = Input[i];

    /* -------------------------------------------------------------------- */
    /*  Find the maximums for each of 16 "columns" of the input.            */
    /* -------------------------------------------------------------------- */

    #ifndef NOASSUME
    #pragma MUST_ITERATE(2,,1);
    #endif
    for (i = 16; i < nInputs; i += 16)
        for (j = 0; j < 16; j++)
            if (Input[i + j] > Max[j]) Max[j] = Input[i + j];

    /* -------------------------------------------------------------------- */
    /*  Find the leftmost "column" with the largest value.                  */
    /* -------------------------------------------------------------------- */
    maxValue = Max[0];
    maxIndex = 0;
    for (i = 0; i < 16; i++)
        if (Max[i] > maxValue)
        {
            maxValue = Max[i];
            maxIndex = i;
        }

    /* -------------------------------------------------------------------- */
    /*  Find the earliest value in the selected column with the max value.  */
    /* -------------------------------------------------------------------- */
    maxLocation = maxIndex;

    #ifndef NOASSUME
    #pragma MUST_ITERATE(2,,1);
    #endif
    for (i = nInputs - 16 + maxIndex; i >= 0; i -= 16)
        if (Input[i] == maxValue) maxLocation = i;

    /* -------------------------------------------------------------------- */
    /*  Return the the location                                             */
    /* -------------------------------------------------------------------- */

    return maxLocation;
}

/* ======================================================================== */
/*  End of file:  dsp_maxidx.c                                              */
/* ------------------------------------------------------------------------ */
/*            Copyright (c) 2003 Texas Instruments, Incorporated.           */
/*                           All Rights Reserved.                           */
/* ======================================================================== */