dsp_fir_sym.h64

来自「dm642函数库」· H64 代码 · 共 129 行

;* ======================================================================== *;
;*  TEXAS INSTRUMENTS, INC.                                                 *;
;*                                                                          *;
;*  DSPLIB  DSP Signal Processing Library                                   *;
;*                                                                          *;
;*      Release:        Revision 1.04b                                      *;
;*      CVS Revision:   1.7     Sun Sep 29 03:32:22 2002 (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_fir_sym -- Symmetric FIR                                        *
*                                                                           *
*   REVISION DATE                                                           *
*       11-Mar-2002                                                         *
*                                                                           *
*   USAGE                                                                   *
*       This function is C callable, and may be called as follows:          *
*                                                                           *
*       void DSP_fir_sym                                                    *
*       (                                                                   *
*           const short * x,      /* Input samples                   */     *
*           const short * h ,     /* Filter taps                     */     *
*           short * restrict r,   /* Output samples                  */     *
*           int nh,               /* Number of symmetric filter taps */     *
*           int nr,               /* Number of output samples        */     *
*           int s                 /* Final output shift.             */     *
*       );                                                                  *
*                                                                           *
*   DESCRIPTION                                                             *
*       This function applies a symmetric filter to the input samples.      *
*       The filter tap array h[] provides 'nh + 1' total filter taps.       *
*       The filter tap at h[nh] forms the center point of the filter.       *
*       The taps at h[nh - 1] through h[0] form a symmetric filter          *
*       about this central tap.  The effective filter length is thus        *
*       2*nh + 1 taps.                                                      *
*                                                                           *
*       The filter is performed on 16-bit data with 16-bit coefficients,    *
*       accumulating intermediate results to 40-bit precision.  The         *
*       accumulator is rounded and truncated according to the value         *
*       provided in 's'.  This allows a variety of Q-points to be used.     *
*                                                                           *
*       Note that samples are added together before multiplication, and     *
*       so overflow *may* result for large-scale values, despite the        *
*       40-bit accumulation.                                                *
*                                                                           *
*   C CODE                                                                  *
*       Below is a C code implementation without restrictions.  The         *
*       optimized implementations have restrictions, as noted under         *
*       "ASSUMPTIONS" and "MEMORY NOTE" below.                              *
*                                                                           *
*       void DSP_fir_sym                                                    *
*       (                                                                   *
*           const short * x,      /* Input samples                   */     *
*           const short * h ,     /* Filter taps                     */     *
*           short * restrict r,   /* Output samples                  */     *
*           int nh,               /* Number of symmetric filter taps */     *
*           int nr,               /* Number of output samples        */     *
*           int s                 /* Final output shift.             */     *
*       )                                                                   *
*       {                                                                   *
*           int  i, j;                                                      *
*           long y0, round = (long) 1 << (s - 1);                           *
*                                                                           *
*           for (j = 0; j < nr; j++)                                        *
*           {                                                               *
*               y0 = round;                                                 *
*                                                                           *
*               for (i = 0; i < nh; i++)                                    *
*                   y0 += ((short) (x[j + i] + x[j + 2 * nh - i])) * h[i];  *
*                                                                           *
*               y0 += x[j + nh] * h[nh];                                    *
*                                                                           *
*               r[j] = (int) (y0 >> s);                                     *
*           }                                                               *
*       }                                                                   *
*                                                                           *
*   ASSUMPTIONS                                                             *
*       The optimized versions of this kernel may assume that nr is         *
*       a multiple of 4 and nh is a multiple of 8.                          *
*                                                                           *
*   MEMORY NOTE.                                                            *
*       The code assumes that 'x' and 'h' are double-word aligned, and      *
*       that 'r' is word alignend.                                          *
*                                                                           *
*       The code expects the device to be in LITTLE ENDIAN mode.            *
*                                                                           *
*   CYCLES                                                                  *
*       cycles = (10 * nh/8 + 15) * nr/4 + 26                               *
*                                                                           *
*   CODESIZE                                                                *
*       664 bytes                                                           *
*                                                                           *
* ------------------------------------------------------------------------- *
*             Copyright (c) 2003 Texas Instruments, Incorporated.           *
*                            All Rights Reserved.                           *
* ========================================================================= *

        .global _DSP_fir_sym

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