;* ======================================================================== *;
;* TEXAS INSTRUMENTS, INC. *;
;* *;
;* DSPLIB DSP Signal Processing Library *;
;* *;
;* Release: Version 1.02 *;
;* CVS Revision: 1.4 Fri Mar 22 02:10:54 2002 (UTC) *;
;* Snapshot date: 18-Apr-2002 *;
;* *;
;* 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) 2002 Texas Instruments, Incorporated. *;
;* All Rights Reserved. *;
;* ======================================================================== *;
* ========================================================================= *
* 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 *
* This code is endian neutral *
* 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 *
* fully interruptible *
* *
* 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 *
* *
* ------------------------------------------------------------------------- *
* Copyright (c) 2002 Texas Instruments, Incorporated. *
* All Rights Reserved. *
* ========================================================================= *
.global _DSP_recip16
* ========================================================================= *
* End of file: dsp_recip16.h62 *
* ------------------------------------------------------------------------- *
* Copyright (c) 2002 Texas Instruments, Incorporated. *
* All Rights Reserved. *
* ========================================================================= *