;* ======================================================================== *;
;* TEXAS INSTRUMENTS, INC. *;
;* *;
;* DSPLIB DSP Signal Processing Library *;
;* *;
;* Release: Version 1.02 *;
;* CVS Revision: 1.3 Fri Mar 22 02:08:27 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_radix2 -- In-place Radix-2 FFT (Little Endian) *
* *
* REVISION DATE *
* 10-Dec-2001 *
* *
* USAGE *
* This routine is C-callable and can be called as: *
* *
* void DSP_radix2(int n, short *restrict xy, *
* const short *restrict w); *
* *
* n -- FFT size (input) *
* xy[] -- input and output sequences (dim-n) (input/output) *
* w[] -- FFT coefficients (dim-n/2) (input) *
* *
* DESCRIPTION *
* This routine is used to compute FFT of a complex sequece of size *
* n, a power of 2, with "decimation-in-frequency decomposition" *
* method, ie, the output is in bit-reversed order. Each complex *
* value is with interleaved 16-bit real and imaginary parts. To *
* prevent overflow, input samples may have to be scaled by 1/n. *
* *
* void DSP_radix2(int n, short *restrict xy, *
* const short *restrict w) *
* { *
* short n1,n2,ie,ia,i,j,k,l; *
* short xt,yt,c,s; *
* *
* n2 = n; *
* ie = 1; *
* for (k=n; k > 1; k = (k >> 1) ) *
* { *
* n1 = n2; *
* n2 = n2>>1; *
* ia = 0; *
* for (j=0; j < n2; j++) *
* { *
* c = w[2*ia]; *
* s = w[2*ia+1]; *
* ia = ia + ie; *
* for (i=j; i < n; i += n1) *
* { *
* l = i + n2; *
* xt = xy[2*l] - xy[2*i]; *
* xy[2*i] = xy[2*i] + xy[2*l]; *
* yt = xy[2*l+1] - xy[2*i+1]; *
* xy[2*i+1] = xy[2*i+1] + xy[2*l+1]; *
* xy[2*l] = (c*xt + s*yt)>>15; *
* xy[2*l+1] = (c*yt - s*xt)>>15; *
* } *
* } *
* ie = ie<<1; *
* } *
* } *
* *
* ASSUMPTIONS *
* 16 <= n <= 32768 *
* Both input xy and coefficient w must be aligned on word boundary. *
* w coef stored ordered is k*(-cos[0*delta]), k*(-sin[0*delta]), *
* k*(-cos[1*delta]), ... where delta = 2*PI/N, k = 32767 *
* Assembly code is written for processor in Little Endian mode *
* Input xy and coefficients w are 16 bit data. *
* *
* MEMORY NOTE *
* Align xy and w on different word boundaries to minimize *
* memory bank hits. *
* *
* TECHNIQUES *
* 1. Loading input xy as well as coefficient w in word. *
* 2. Both loops j and i shown in the C code are placed in the *
* INNERLOOP of the assembly code. *
* *
* CYCLES *
* cycles = log2(N) * (4*N/2+7) + 34 + N/4. *
* *
* (The N/4 term is due to bank conflicts that occur when xy and w *
* are aligned as suggested above, under "MEMORY NOTE.") *
* *
* For N = 256, cycles = 4250. *
* *
* CODESIZE *
* 800 bytes *
* *
* ------------------------------------------------------------------------- *
* Copyright (c) 2002 Texas Instruments, Incorporated. *
* All Rights Reserved. *
* ========================================================================= *
.global _DSP_radix2
* ========================================================================= *
* End of file: dsp_radix2.h62 *
* ------------------------------------------------------------------------- *
* Copyright (c) 2002 Texas Instruments, Incorporated. *
* All Rights Reserved. *
* ========================================================================= *