dsp_maxidx.h64

来自「dm642函数库」· H64 代码 · 共 132 行

;* ======================================================================== *;
;*  TEXAS INSTRUMENTS, INC.                                                 *;
;*                                                                          *;
;*  DSPLIB  DSP Signal Processing Library                                   *;
;*                                                                          *;
;*      Release:        Revision 1.04b                                      *;
;*      CVS Revision:   1.8     Mon Jul 28 13:15:23 2003 (UTC)              *;
;*      Snapshot date:  23-Oct-2003                                         *;
;*                                                                          *;
;*  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.                            *;
;* ======================================================================== *;
;* ======================================================================== *;
;*  Assembler compatibility shim for assembling 4.30 and later code on      *;
;*  tools prior to 4.30.                                                    *;
;* ======================================================================== *;
;* ======================================================================== *;
;*  End of assembler compatibility shim.                                    *;
;* ======================================================================== *;
* ========================================================================= *
*   TEXAS INSTRUMENTS, INC.                                                 *
*                                                                           *
*   NAME                                                                    *
*       DSP_maxidx                                                          *
*                                                                           *
*   REVISION DATE                                                           *
*       23-Jul-2003                                                         *
*                                                                           *
*   USAGE                                                                   *
*       This routine is C callable, and has the following C prototype:      *
*                                                                           *
*           int DSP_maxidx(const short *x, int nx);                         *
*                                                                           *
*           x       = pointer to input data                                 *
*           nx      = number of samples                                     *
*           return  = max index                                             *
*                                                                           *
*   DESCRIPTION                                                             *
*       This routine finds the maximum value of the vector x[ ] and         *
*       returns the index of that value.                                    *
*                                                                           *
*       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.                                 *
*                                                                           *
*           int DSP_maxidx(const short *x, int nx)                          *
*           {                                                               *
*               int col, idx;                                               *
*               short max_val;                                              *
*               int   max_idx;                                              *
*                                                                           *
*               max_val = x[0];                                             *
*               max_idx = 0;                                                *
*                                                                           *
*               for (col = 0; col < 16; col++)                              *
*                   for (idx = col; idx < nx; idx += 16)                    *
*                       if (x[idx] > max_val)                               *
*                       {                                                   *
*                           max_val = x[idx];                               *
*                           max_idx = idx;                                  *
*                       }                                                   *
*                                                                           *
*               return max_idx;                                             *
*           }                                                               *
*                                                                           *
*       The above C code is a general implementation without                *
*       restrictions.  The assembly code has some restrictions, as          *
*       noted below.                                                        *
*                                                                           *
*   TECHNIQUES                                                              *
*       The code is unrolled 16 times to enable the full bandwidth of       *
*       LDDW and MAX2 instructions to be utilized.  This splits the         *
*       search into 16 subranges.  The global maximum is then found         *
*       from the list of maximums of the subsranges.                        *
*                                                                           *
*       Then using this offset from the subranges, the global maximum       *
*       and the index of it are found using a simple match.                 *
*                                                                           *
*       For common maximums in multiple ranges, the index will be           *
*       different to the above C code.                                      *
*                                                                           *
*   ASSUMPTIONS                                                             *
*       The input data are stored on double-word aligned boundaries.        *
*       nx must be a multiple of 16 and >= 48                               *
*                                                                           *
*   MEMORY NOTE                                                             *
*       There are no bank conflicts in this code.                           *
*                                                                           *
*       This code is ENDIAN NEUTRAL.                                        *
*                                                                           *
*       This code requires 40 bytes of stack space for a temporary          *
*       buffer.                                                             *
*                                                                           *
*   NOTES                                                                   *
*       Interupts are disabled for the duration of this function.           *
*                                                                           *
*   CYCLES                                                                  *
*       5/16 * nx + 42                                                      *
*       For nx = 128, cycles = 82.                                          *
*                                                                           *
*   CODESIZE                                                                *
*       388 bytes                                                           *
*                                                                           *
* ------------------------------------------------------------------------- *
*             Copyright (c) 2003 Texas Instruments, Incorporated.           *
*                            All Rights Reserved.                           *
* ========================================================================= *

        .global _DSP_maxidx

* ========================================================================= *
*   End of file:  dsp_maxidx.h64                                            *
* ------------------------------------------------------------------------- *
*             Copyright (c) 2003 Texas Instruments, Incorporated.           *
*                            All Rights Reserved.                           *
* ========================================================================= *