dsp_recip16.h64

来自「dm642函数库」· H64 代码 · 共 126 行

;* ======================================================================== *;
;*  TEXAS INSTRUMENTS, INC.                                                 *;
;*                                                                          *;
;*  DSPLIB  DSP Signal Processing Library                                   *;
;*                                                                          *;
;*      Release:        Revision 1.04b                                      *;
;*      CVS Revision:   1.5     Sun Sep 29 03:32:28 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_recip16                                                         *
*                                                                           *
*                                                                           *
*   REVISION DATE                                                           *
*       20-Jul-2001                                                         *
*                                                                           *
*   USAGE                                                                   *
*       This routine is C-callable and can be called as:                    *
*                                                                           *
*       void DSP_recip16 (short *x, short *rfrac, short *rexp, short nx);   *
*                                                                           *
*       x[nx]     = Pointer to input vector of size nx                      *
*       rfrac[nx] = Pointer to output vector of size nx to                  *
*                   contain the fractional part of the reciprocal           *
*       rexp[nx]  = Pointer to output vector of size nx to                  *
*                   contain the exponent part of the reciprocal             *
*       nx        = Number of elements in input vector                      *
*                                                                           *
*       (See the C compiler reference guide.)                               *
*                                                                           *
*   DESCRIPTION                                                             *
*       This program performs a reciprocal on a vector of Q15 numbers.      *
*       The result is stored in two parts: a Q15 part and an exponent       *
*       (power of two) of the fraction.                                     *
*       First, the input is loaded, then its absolute value is taken,       *
*       then it is normalized, then divided using a loop of conditional     *
*       subtracts, and finally it is negated if the original input was      *
*       negative.                                                           *
*                                                                           *
*       void DSP_recip16 (short *x, short *rfrac, short *rexp, short nx)    *
*       {                                                                   *
*          int i,j,a,b;                                                     *
*          short neg, normal;                                               *
*                                                                           *
*          for(i = nx; i > 0; i--)                                          *
*          {                                                                *
*              a = *(x++);                                                  *
*              if(a < 0)             /* take absolute value */              *
*              {                                                            *
*                  a = -a;                                                  *
*                  neg = 1;                                                 *
*              }                                                            *
*              else                                                         *
*                  neg = 0;                                                 *
*              normal = _norm(a);              /* normalize */              *
*              a = a << normal;                                             *
*              *(rexp++) = normal - 15;   /* store exponent */              *
*              b = 0x80000000;              /* dividend = 1 */              *
*              for(j = 15; j > 0; j--)                                      *
*                  b = _subc(b,a);                /* divide */              *
*              b = b & 0x7FFF;           /* clear remainder */              *
*              if(neg) b = -b;       /* if negative, negate */              *
*              *(rfrac++) = b;            /* store fraction */              *
*          }                                                                *
*       }                                                                   *
*                                                                           *
*   ASSUMPTIONS                                                             *
*       LITTLE ENDIAN Configuration used                                    *
*       x and rfrac are Q15 format                                          *
*       output is accurate up to the least significant bit of rfrac, but    *
*       note that this bit could carry over and change rexp too             *
*                                                                           *
*   MEMORY NOTE                                                             *
*       There are no memory bank hits in this procedure                     *
*                                                                           *
*   NOTE                                                                    *
*       interruptible (single assignment code)                              *
*                                                                           *
*   TECHNIQUES                                                              *
*       The conditional subtract instruction, SUBC, is used for division    *
*       SUBC is used once for every bit of quotient needed (15).            *
*       2 stages of prolog and epilog collapsed                             *
*       split 2 live-too-longs (A_neg and B_norm)                           *
*                                                                           *
*   CYCLES                                                                  *
*        8 * nx + 14                                                        *
*                                                                           *
*   CODESIZE                                                                *
*        196 bytes                                                          *
* ------------------------------------------------------------------------- *
*             Copyright (c) 2003 Texas Instruments, Incorporated.           *
*                            All Rights Reserved.                           *
* ========================================================================= *

        .global _DSP_recip16

* ========================================================================= *
*   End of file:  dsp_recip16.h64                                           *
* ------------------------------------------------------------------------- *
*             Copyright (c) 2003 Texas Instruments, Incorporated.           *
*                            All Rights Reserved.                           *
* ========================================================================= *