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CMSIS DSP library

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cmsis_dsp/TransformFunctions/arm_rfft_fast_f32.c@5:3762170b6d4d, 2015-11-20 (annotated)

Committer:
mbed_official
Date:
Fri Nov 20 08:45:18 2015 +0000
Revision:
5:3762170b6d4d
Parent:
3:7a284390b0ce 
Synchronized with git revision 2eb940b9a73af188d3004a2575fdfbb05febe62b



Full URL: https://github.com/mbedmicro/mbed/commit/2eb940b9a73af188d3004a2575fdfbb05febe62b/



Added option to build rpc library. closes #1426

Who changed what in which revision?

UserRevisionLine numberNew contents of line
mbed_official 3:7a284390b0ce 1 /* ----------------------------------------------------------------------
mbed_official 5:3762170b6d4d 2 * Copyright (C) 2010-2014 ARM Limited. All rights reserved.
mbed_official 3:7a284390b0ce 3 *
mbed_official 5:3762170b6d4d 4 * $Date: 19. March 2015
mbed_official 5:3762170b6d4d 5 * $Revision: V.1.4.5
mbed_official 3:7a284390b0ce 6 *
mbed_official 3:7a284390b0ce 7 * Project: CMSIS DSP Library
mbed_official 3:7a284390b0ce 8 * Title: arm_rfft_f32.c
mbed_official 3:7a284390b0ce 9 *
mbed_official 3:7a284390b0ce 10 * Description: RFFT & RIFFT Floating point process function
mbed_official 3:7a284390b0ce 11 *
mbed_official 3:7a284390b0ce 12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
mbed_official 3:7a284390b0ce 13 *
mbed_official 3:7a284390b0ce 14 * Redistribution and use in source and binary forms, with or without
mbed_official 3:7a284390b0ce 15 * modification, are permitted provided that the following conditions
mbed_official 3:7a284390b0ce 16 * are met:
mbed_official 3:7a284390b0ce 17 * - Redistributions of source code must retain the above copyright
mbed_official 3:7a284390b0ce 18 * notice, this list of conditions and the following disclaimer.
mbed_official 3:7a284390b0ce 19 * - Redistributions in binary form must reproduce the above copyright
mbed_official 3:7a284390b0ce 20 * notice, this list of conditions and the following disclaimer in
mbed_official 3:7a284390b0ce 21 * the documentation and/or other materials provided with the
mbed_official 3:7a284390b0ce 22 * distribution.
mbed_official 3:7a284390b0ce 23 * - Neither the name of ARM LIMITED nor the names of its contributors
mbed_official 3:7a284390b0ce 24 * may be used to endorse or promote products derived from this
mbed_official 3:7a284390b0ce 25 * software without specific prior written permission.
mbed_official 3:7a284390b0ce 26 *
mbed_official 3:7a284390b0ce 27 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
mbed_official 3:7a284390b0ce 28 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
mbed_official 3:7a284390b0ce 29 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
mbed_official 3:7a284390b0ce 30 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
mbed_official 3:7a284390b0ce 31 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
mbed_official 3:7a284390b0ce 32 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
mbed_official 3:7a284390b0ce 33 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
mbed_official 3:7a284390b0ce 34 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
mbed_official 3:7a284390b0ce 35 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
mbed_official 3:7a284390b0ce 36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
mbed_official 3:7a284390b0ce 37 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
mbed_official 3:7a284390b0ce 38 * POSSIBILITY OF SUCH DAMAGE.
mbed_official 3:7a284390b0ce 39 * -------------------------------------------------------------------- */
mbed_official 3:7a284390b0ce 40
mbed_official 3:7a284390b0ce 41 #include "arm_math.h"
mbed_official 3:7a284390b0ce 42
mbed_official 3:7a284390b0ce 43 void stage_rfft_f32(
mbed_official 3:7a284390b0ce 44 arm_rfft_fast_instance_f32 * S,
mbed_official 3:7a284390b0ce 45 float32_t * p, float32_t * pOut)
mbed_official 3:7a284390b0ce 46 {
mbed_official 3:7a284390b0ce 47 uint32_t k; /* Loop Counter */
mbed_official 3:7a284390b0ce 48 float32_t twR, twI; /* RFFT Twiddle coefficients */
mbed_official 3:7a284390b0ce 49 float32_t * pCoeff = S->pTwiddleRFFT; /* Points to RFFT Twiddle factors */
mbed_official 3:7a284390b0ce 50 float32_t *pA = p; /* increasing pointer */
mbed_official 3:7a284390b0ce 51 float32_t *pB = p; /* decreasing pointer */
mbed_official 3:7a284390b0ce 52 float32_t xAR, xAI, xBR, xBI; /* temporary variables */
mbed_official 3:7a284390b0ce 53 float32_t t1a, t1b; /* temporary variables */
mbed_official 3:7a284390b0ce 54 float32_t p0, p1, p2, p3; /* temporary variables */
mbed_official 3:7a284390b0ce 55
mbed_official 3:7a284390b0ce 56
mbed_official 3:7a284390b0ce 57 k = (S->Sint).fftLen - 1;
mbed_official 3:7a284390b0ce 58
mbed_official 3:7a284390b0ce 59 /* Pack first and last sample of the frequency domain together */
mbed_official 3:7a284390b0ce 60
mbed_official 3:7a284390b0ce 61 xBR = pB[0];
mbed_official 3:7a284390b0ce 62 xBI = pB[1];
mbed_official 3:7a284390b0ce 63 xAR = pA[0];
mbed_official 3:7a284390b0ce 64 xAI = pA[1];
mbed_official 3:7a284390b0ce 65
mbed_official 3:7a284390b0ce 66 twR = *pCoeff++ ;
mbed_official 3:7a284390b0ce 67 twI = *pCoeff++ ;
mbed_official 3:7a284390b0ce 68
mbed_official 3:7a284390b0ce 69 // U1 = XA(1) + XB(1); % It is real
mbed_official 3:7a284390b0ce 70 t1a = xBR + xAR ;
mbed_official 3:7a284390b0ce 71
mbed_official 3:7a284390b0ce 72 // U2 = XB(1) - XA(1); % It is imaginary
mbed_official 3:7a284390b0ce 73 t1b = xBI + xAI ;
mbed_official 3:7a284390b0ce 74
mbed_official 3:7a284390b0ce 75 // real(tw * (xB - xA)) = twR * (xBR - xAR) - twI * (xBI - xAI);
mbed_official 3:7a284390b0ce 76 // imag(tw * (xB - xA)) = twI * (xBR - xAR) + twR * (xBI - xAI);
mbed_official 3:7a284390b0ce 77 *pOut++ = 0.5f * ( t1a + t1b );
mbed_official 3:7a284390b0ce 78 *pOut++ = 0.5f * ( t1a - t1b );
mbed_official 3:7a284390b0ce 79
mbed_official 3:7a284390b0ce 80 // XA(1) = 1/2*( U1 - imag(U2) + i*( U1 +imag(U2) ));
mbed_official 3:7a284390b0ce 81 pB = p + 2*k;
mbed_official 3:7a284390b0ce 82 pA += 2;
mbed_official 3:7a284390b0ce 83
mbed_official 3:7a284390b0ce 84 do
mbed_official 3:7a284390b0ce 85 {
mbed_official 3:7a284390b0ce 86 /*
mbed_official 3:7a284390b0ce 87 function X = my_split_rfft(X, ifftFlag)
mbed_official 3:7a284390b0ce 88 % X is a series of real numbers
mbed_official 3:7a284390b0ce 89 L = length(X);
mbed_official 3:7a284390b0ce 90 XC = X(1:2:end) +i*X(2:2:end);
mbed_official 3:7a284390b0ce 91 XA = fft(XC);
mbed_official 3:7a284390b0ce 92 XB = conj(XA([1 end:-1:2]));
mbed_official 3:7a284390b0ce 93 TW = i*exp(-2*pi*i*[0:L/2-1]/L).';
mbed_official 3:7a284390b0ce 94 for l = 2:L/2
mbed_official 3:7a284390b0ce 95 XA(l) = 1/2 * (XA(l) + XB(l) + TW(l) * (XB(l) - XA(l)));
mbed_official 3:7a284390b0ce 96 end
mbed_official 3:7a284390b0ce 97 XA(1) = 1/2* (XA(1) + XB(1) + TW(1) * (XB(1) - XA(1))) + i*( 1/2*( XA(1) + XB(1) + i*( XA(1) - XB(1))));
mbed_official 3:7a284390b0ce 98 X = XA;
mbed_official 3:7a284390b0ce 99 */
mbed_official 3:7a284390b0ce 100
mbed_official 3:7a284390b0ce 101 xBI = pB[1];
mbed_official 3:7a284390b0ce 102 xBR = pB[0];
mbed_official 3:7a284390b0ce 103 xAR = pA[0];
mbed_official 3:7a284390b0ce 104 xAI = pA[1];
mbed_official 3:7a284390b0ce 105
mbed_official 3:7a284390b0ce 106 twR = *pCoeff++;
mbed_official 3:7a284390b0ce 107 twI = *pCoeff++;
mbed_official 3:7a284390b0ce 108
mbed_official 3:7a284390b0ce 109 t1a = xBR - xAR ;
mbed_official 3:7a284390b0ce 110 t1b = xBI + xAI ;
mbed_official 3:7a284390b0ce 111
mbed_official 3:7a284390b0ce 112 // real(tw * (xB - xA)) = twR * (xBR - xAR) - twI * (xBI - xAI);
mbed_official 3:7a284390b0ce 113 // imag(tw * (xB - xA)) = twI * (xBR - xAR) + twR * (xBI - xAI);
mbed_official 3:7a284390b0ce 114 p0 = twR * t1a;
mbed_official 3:7a284390b0ce 115 p1 = twI * t1a;
mbed_official 3:7a284390b0ce 116 p2 = twR * t1b;
mbed_official 3:7a284390b0ce 117 p3 = twI * t1b;
mbed_official 3:7a284390b0ce 118
mbed_official 3:7a284390b0ce 119 *pOut++ = 0.5f * (xAR + xBR + p0 + p3 ); //xAR
mbed_official 3:7a284390b0ce 120 *pOut++ = 0.5f * (xAI - xBI + p1 - p2 ); //xAI
mbed_official 3:7a284390b0ce 121
mbed_official 3:7a284390b0ce 122 pA += 2;
mbed_official 3:7a284390b0ce 123 pB -= 2;
mbed_official 3:7a284390b0ce 124 k--;
mbed_official 3:7a284390b0ce 125 } while(k > 0u);
mbed_official 3:7a284390b0ce 126 }
mbed_official 3:7a284390b0ce 127
mbed_official 3:7a284390b0ce 128 /* Prepares data for inverse cfft */
mbed_official 3:7a284390b0ce 129 void merge_rfft_f32(
mbed_official 3:7a284390b0ce 130 arm_rfft_fast_instance_f32 * S,
mbed_official 3:7a284390b0ce 131 float32_t * p, float32_t * pOut)
mbed_official 3:7a284390b0ce 132 {
mbed_official 3:7a284390b0ce 133 uint32_t k; /* Loop Counter */
mbed_official 3:7a284390b0ce 134 float32_t twR, twI; /* RFFT Twiddle coefficients */
mbed_official 3:7a284390b0ce 135 float32_t *pCoeff = S->pTwiddleRFFT; /* Points to RFFT Twiddle factors */
mbed_official 3:7a284390b0ce 136 float32_t *pA = p; /* increasing pointer */
mbed_official 3:7a284390b0ce 137 float32_t *pB = p; /* decreasing pointer */
mbed_official 3:7a284390b0ce 138 float32_t xAR, xAI, xBR, xBI; /* temporary variables */
mbed_official 3:7a284390b0ce 139 float32_t t1a, t1b, r, s, t, u; /* temporary variables */
mbed_official 3:7a284390b0ce 140
mbed_official 3:7a284390b0ce 141 k = (S->Sint).fftLen - 1;
mbed_official 3:7a284390b0ce 142
mbed_official 3:7a284390b0ce 143 xAR = pA[0];
mbed_official 3:7a284390b0ce 144 xAI = pA[1];
mbed_official 3:7a284390b0ce 145
mbed_official 3:7a284390b0ce 146 pCoeff += 2 ;
mbed_official 3:7a284390b0ce 147
mbed_official 3:7a284390b0ce 148 *pOut++ = 0.5f * ( xAR + xAI );
mbed_official 3:7a284390b0ce 149 *pOut++ = 0.5f * ( xAR - xAI );
mbed_official 3:7a284390b0ce 150
mbed_official 3:7a284390b0ce 151 pB = p + 2*k ;
mbed_official 3:7a284390b0ce 152 pA += 2 ;
mbed_official 3:7a284390b0ce 153
mbed_official 3:7a284390b0ce 154 while(k > 0u)
mbed_official 3:7a284390b0ce 155 {
mbed_official 3:7a284390b0ce 156 /* G is half of the frequency complex spectrum */
mbed_official 3:7a284390b0ce 157 //for k = 2:N
mbed_official 3:7a284390b0ce 158 // Xk(k) = 1/2 * (G(k) + conj(G(N-k+2)) + Tw(k)*( G(k) - conj(G(N-k+2))));
mbed_official 3:7a284390b0ce 159 xBI = pB[1] ;
mbed_official 3:7a284390b0ce 160 xBR = pB[0] ;
mbed_official 3:7a284390b0ce 161 xAR = pA[0];
mbed_official 3:7a284390b0ce 162 xAI = pA[1];
mbed_official 3:7a284390b0ce 163
mbed_official 3:7a284390b0ce 164 twR = *pCoeff++;
mbed_official 3:7a284390b0ce 165 twI = *pCoeff++;
mbed_official 3:7a284390b0ce 166
mbed_official 3:7a284390b0ce 167 t1a = xAR - xBR ;
mbed_official 3:7a284390b0ce 168 t1b = xAI + xBI ;
mbed_official 3:7a284390b0ce 169
mbed_official 3:7a284390b0ce 170 r = twR * t1a;
mbed_official 3:7a284390b0ce 171 s = twI * t1b;
mbed_official 3:7a284390b0ce 172 t = twI * t1a;
mbed_official 3:7a284390b0ce 173 u = twR * t1b;
mbed_official 3:7a284390b0ce 174
mbed_official 3:7a284390b0ce 175 // real(tw * (xA - xB)) = twR * (xAR - xBR) - twI * (xAI - xBI);
mbed_official 3:7a284390b0ce 176 // imag(tw * (xA - xB)) = twI * (xAR - xBR) + twR * (xAI - xBI);
mbed_official 3:7a284390b0ce 177 *pOut++ = 0.5f * (xAR + xBR - r - s ); //xAR
mbed_official 3:7a284390b0ce 178 *pOut++ = 0.5f * (xAI - xBI + t - u ); //xAI
mbed_official 3:7a284390b0ce 179
mbed_official 3:7a284390b0ce 180 pA += 2;
mbed_official 3:7a284390b0ce 181 pB -= 2;
mbed_official 3:7a284390b0ce 182 k--;
mbed_official 3:7a284390b0ce 183 }
mbed_official 3:7a284390b0ce 184
mbed_official 3:7a284390b0ce 185 }
mbed_official 3:7a284390b0ce 186
mbed_official 3:7a284390b0ce 187 /**
mbed_official 3:7a284390b0ce 188 * @ingroup groupTransforms
mbed_official 3:7a284390b0ce 189 */
mbed_official 3:7a284390b0ce 190
mbed_official 3:7a284390b0ce 191 /**
mbed_official 3:7a284390b0ce 192 * @defgroup Fast Real FFT Functions
mbed_official 3:7a284390b0ce 193 *
mbed_official 3:7a284390b0ce 194 * \par
mbed_official 3:7a284390b0ce 195 * The CMSIS DSP library includes specialized algorithms for computing the
mbed_official 3:7a284390b0ce 196 * FFT of real data sequences. The FFT is defined over complex data but
mbed_official 3:7a284390b0ce 197 * in many applications the input is real. Real FFT algorithms take advantage
mbed_official 3:7a284390b0ce 198 * of the symmetry properties of the FFT and have a speed advantage over complex
mbed_official 3:7a284390b0ce 199 * algorithms of the same length.
mbed_official 3:7a284390b0ce 200 * \par
mbed_official 3:7a284390b0ce 201 * The Fast RFFT algorith relays on the mixed radix CFFT that save processor usage.
mbed_official 3:7a284390b0ce 202 * \par
mbed_official 3:7a284390b0ce 203 * The real length N forward FFT of a sequence is computed using the steps shown below.
mbed_official 3:7a284390b0ce 204 * \par
mbed_official 3:7a284390b0ce 205 * \image html RFFT.gif "Real Fast Fourier Transform"
mbed_official 3:7a284390b0ce 206 * \par
mbed_official 3:7a284390b0ce 207 * The real sequence is initially treated as if it were complex to perform a CFFT.
mbed_official 3:7a284390b0ce 208 * Later, a processing stage reshapes the data to obtain half of the frequency spectrum
mbed_official 3:7a284390b0ce 209 * in complex format. Except the first complex number that contains the two real numbers
mbed_official 3:7a284390b0ce 210 * X[0] and X[N/2] all the data is complex. In other words, the first complex sample
mbed_official 3:7a284390b0ce 211 * contains two real values packed.
mbed_official 3:7a284390b0ce 212 * \par
mbed_official 3:7a284390b0ce 213 * The input for the inverse RFFT should keep the same format as the output of the
mbed_official 3:7a284390b0ce 214 * forward RFFT. A first processing stage pre-process the data to later perform an
mbed_official 3:7a284390b0ce 215 * inverse CFFT.
mbed_official 3:7a284390b0ce 216 * \par
mbed_official 3:7a284390b0ce 217 * \image html RIFFT.gif "Real Inverse Fast Fourier Transform"
mbed_official 3:7a284390b0ce 218 * \par
mbed_official 3:7a284390b0ce 219 * The algorithms for floating-point, Q15, and Q31 data are slightly different
mbed_official 3:7a284390b0ce 220 * and we describe each algorithm in turn.
mbed_official 3:7a284390b0ce 221 * \par Floating-point
mbed_official 3:7a284390b0ce 222 * The main functions are <code>arm_rfft_fast_f32()</code>
mbed_official 3:7a284390b0ce 223 * and <code>arm_rfft_fast_init_f32()</code>. The older functions
mbed_official 3:7a284390b0ce 224 * <code>arm_rfft_f32()</code> and <code>arm_rfft_init_f32()</code> have been
mbed_official 3:7a284390b0ce 225 * deprecated but are still documented.
mbed_official 3:7a284390b0ce 226 * \par
mbed_official 3:7a284390b0ce 227 * The FFT of a real N-point sequence has even symmetry in the frequency
mbed_official 3:7a284390b0ce 228 * domain. The second half of the data equals the conjugate of the first half
mbed_official 3:7a284390b0ce 229 * flipped in frequency:
mbed_official 3:7a284390b0ce 230 * <pre>
mbed_official 3:7a284390b0ce 231 *X[0] - real data
mbed_official 3:7a284390b0ce 232 *X[1] - complex data
mbed_official 3:7a284390b0ce 233 *X[2] - complex data
mbed_official 3:7a284390b0ce 234 *...
mbed_official 3:7a284390b0ce 235 *X[fftLen/2-1] - complex data
mbed_official 3:7a284390b0ce 236 *X[fftLen/2] - real data
mbed_official 3:7a284390b0ce 237 *X[fftLen/2+1] - conjugate of X[fftLen/2-1]
mbed_official 3:7a284390b0ce 238 *X[fftLen/2+2] - conjugate of X[fftLen/2-2]
mbed_official 3:7a284390b0ce 239 *...
mbed_official 3:7a284390b0ce 240 *X[fftLen-1] - conjugate of X[1]
mbed_official 3:7a284390b0ce 241 * </pre>
mbed_official 3:7a284390b0ce 242 * Looking at the data, we see that we can uniquely represent the FFT using only
mbed_official 3:7a284390b0ce 243 * <pre>
mbed_official 3:7a284390b0ce 244 *N/2+1 samples:
mbed_official 3:7a284390b0ce 245 *X[0] - real data
mbed_official 3:7a284390b0ce 246 *X[1] - complex data
mbed_official 3:7a284390b0ce 247 *X[2] - complex data
mbed_official 3:7a284390b0ce 248 *...
mbed_official 3:7a284390b0ce 249 *X[fftLen/2-1] - complex data
mbed_official 3:7a284390b0ce 250 *X[fftLen/2] - real data
mbed_official 3:7a284390b0ce 251 * </pre>
mbed_official 3:7a284390b0ce 252 * Looking more closely we see that the first and last samples are real valued.
mbed_official 3:7a284390b0ce 253 * They can be packed together and we can thus represent the FFT of an N-point
mbed_official 3:7a284390b0ce 254 * real sequence by N/2 complex values:
mbed_official 3:7a284390b0ce 255 * <pre>
mbed_official 3:7a284390b0ce 256 *X[0],X[N/2] - packed real data: X[0] + jX[N/2]
mbed_official 3:7a284390b0ce 257 *X[1] - complex data
mbed_official 3:7a284390b0ce 258 *X[2] - complex data
mbed_official 3:7a284390b0ce 259 *...
mbed_official 3:7a284390b0ce 260 *X[fftLen/2-1] - complex data
mbed_official 3:7a284390b0ce 261 * </pre>
mbed_official 3:7a284390b0ce 262 * The real FFT functions pack the frequency domain data in this fashion. The
mbed_official 3:7a284390b0ce 263 * forward transform outputs the data in this form and the inverse transform
mbed_official 3:7a284390b0ce 264 * expects input data in this form. The function always performs the needed
mbed_official 3:7a284390b0ce 265 * bitreversal so that the input and output data is always in normal order. The
mbed_official 3:7a284390b0ce 266 * functions support lengths of [32, 64, 128, ..., 4096] samples.
mbed_official 3:7a284390b0ce 267 * \par
mbed_official 3:7a284390b0ce 268 * The forward and inverse real FFT functions apply the standard FFT scaling; no
mbed_official 3:7a284390b0ce 269 * scaling on the forward transform and 1/fftLen scaling on the inverse
mbed_official 3:7a284390b0ce 270 * transform.
mbed_official 3:7a284390b0ce 271 * \par Q15 and Q31
mbed_official 3:7a284390b0ce 272 * The real algorithms are defined in a similar manner and utilize N/2 complex
mbed_official 5:3762170b6d4d 273 * transforms behind the scenes.
mbed_official 3:7a284390b0ce 274 * \par
mbed_official 3:7a284390b0ce 275 * The complex transforms used internally include scaling to prevent fixed-point
mbed_official 3:7a284390b0ce 276 * overflows. The overall scaling equals 1/(fftLen/2).
mbed_official 3:7a284390b0ce 277 * \par
mbed_official 3:7a284390b0ce 278 * A separate instance structure must be defined for each transform used but
mbed_official 3:7a284390b0ce 279 * twiddle factor and bit reversal tables can be reused.
mbed_official 3:7a284390b0ce 280 * \par
mbed_official 3:7a284390b0ce 281 * There is also an associated initialization function for each data type.
mbed_official 3:7a284390b0ce 282 * The initialization function performs the following operations:
mbed_official 3:7a284390b0ce 283 * - Sets the values of the internal structure fields.
mbed_official 3:7a284390b0ce 284 * - Initializes twiddle factor table and bit reversal table pointers.
mbed_official 3:7a284390b0ce 285 * - Initializes the internal complex FFT data structure.
mbed_official 3:7a284390b0ce 286 * \par
mbed_official 3:7a284390b0ce 287 * Use of the initialization function is optional.
mbed_official 3:7a284390b0ce 288 * However, if the initialization function is used, then the instance structure
mbed_official 3:7a284390b0ce 289 * cannot be placed into a const data section. To place an instance structure
mbed_official 3:7a284390b0ce 290 * into a const data section, the instance structure should be manually
mbed_official 3:7a284390b0ce 291 * initialized as follows:
mbed_official 3:7a284390b0ce 292 * <pre>
mbed_official 3:7a284390b0ce 293 *arm_rfft_instance_q31 S = {fftLenReal, fftLenBy2, ifftFlagR, bitReverseFlagR, twidCoefRModifier, pTwiddleAReal, pTwiddleBReal, pCfft};
mbed_official 3:7a284390b0ce 294 *arm_rfft_instance_q15 S = {fftLenReal, fftLenBy2, ifftFlagR, bitReverseFlagR, twidCoefRModifier, pTwiddleAReal, pTwiddleBReal, pCfft};
mbed_official 3:7a284390b0ce 295 * </pre>
mbed_official 3:7a284390b0ce 296 * where <code>fftLenReal</code> is the length of the real transform;
mbed_official 3:7a284390b0ce 297 * <code>fftLenBy2</code> length of the internal complex transform.
mbed_official 3:7a284390b0ce 298 * <code>ifftFlagR</code> Selects forward (=0) or inverse (=1) transform.
mbed_official 3:7a284390b0ce 299 * <code>bitReverseFlagR</code> Selects bit reversed output (=0) or normal order
mbed_official 3:7a284390b0ce 300 * output (=1).
mbed_official 3:7a284390b0ce 301 * <code>twidCoefRModifier</code> stride modifier for the twiddle factor table.
mbed_official 3:7a284390b0ce 302 * The value is based on the FFT length;
mbed_official 3:7a284390b0ce 303 * <code>pTwiddleAReal</code>points to the A array of twiddle coefficients;
mbed_official 3:7a284390b0ce 304 * <code>pTwiddleBReal</code>points to the B array of twiddle coefficients;
mbed_official 3:7a284390b0ce 305 * <code>pCfft</code> points to the CFFT Instance structure. The CFFT structure
mbed_official 3:7a284390b0ce 306 * must also be initialized. Refer to arm_cfft_radix4_f32() for details regarding
mbed_official 3:7a284390b0ce 307 * static initialization of the complex FFT instance structure.
mbed_official 3:7a284390b0ce 308 */
mbed_official 3:7a284390b0ce 309
mbed_official 3:7a284390b0ce 310 /**
mbed_official 3:7a284390b0ce 311 * @addtogroup RealFFT
mbed_official 3:7a284390b0ce 312 * @{
mbed_official 3:7a284390b0ce 313 */
mbed_official 3:7a284390b0ce 314
mbed_official 3:7a284390b0ce 315 /**
mbed_official 3:7a284390b0ce 316 * @brief Processing function for the floating-point real FFT.
mbed_official 3:7a284390b0ce 317 * @param[in] *S points to an arm_rfft_fast_instance_f32 structure.
mbed_official 3:7a284390b0ce 318 * @param[in] *p points to the input buffer.
mbed_official 5:3762170b6d4d 319 * @param[in] *pOut points to the output buffer.
mbed_official 3:7a284390b0ce 320 * @param[in] ifftFlag RFFT if flag is 0, RIFFT if flag is 1
mbed_official 3:7a284390b0ce 321 * @return none.
mbed_official 3:7a284390b0ce 322 */
mbed_official 3:7a284390b0ce 323
mbed_official 3:7a284390b0ce 324 void arm_rfft_fast_f32(
mbed_official 3:7a284390b0ce 325 arm_rfft_fast_instance_f32 * S,
mbed_official 3:7a284390b0ce 326 float32_t * p, float32_t * pOut,
mbed_official 3:7a284390b0ce 327 uint8_t ifftFlag)
mbed_official 3:7a284390b0ce 328 {
mbed_official 3:7a284390b0ce 329 arm_cfft_instance_f32 * Sint = &(S->Sint);
mbed_official 3:7a284390b0ce 330 Sint->fftLen = S->fftLenRFFT / 2;
mbed_official 3:7a284390b0ce 331
mbed_official 3:7a284390b0ce 332 /* Calculation of Real FFT */
mbed_official 3:7a284390b0ce 333 if(ifftFlag)
mbed_official 3:7a284390b0ce 334 {
mbed_official 5:3762170b6d4d 335 /* Real FFT compression */
mbed_official 3:7a284390b0ce 336 merge_rfft_f32(S, p, pOut);
mbed_official 3:7a284390b0ce 337
mbed_official 3:7a284390b0ce 338 /* Complex radix-4 IFFT process */
mbed_official 3:7a284390b0ce 339 arm_cfft_f32( Sint, pOut, ifftFlag, 1);
mbed_official 3:7a284390b0ce 340 }
mbed_official 3:7a284390b0ce 341 else
mbed_official 3:7a284390b0ce 342 {
mbed_official 3:7a284390b0ce 343 /* Calculation of RFFT of input */
mbed_official 3:7a284390b0ce 344 arm_cfft_f32( Sint, p, ifftFlag, 1);
mbed_official 3:7a284390b0ce 345
mbed_official 3:7a284390b0ce 346 /* Real FFT extraction */
mbed_official 3:7a284390b0ce 347 stage_rfft_f32(S, p, pOut);
mbed_official 3:7a284390b0ce 348 }
mbed_official 3:7a284390b0ce 349 }
mbed_official 3:7a284390b0ce 350
mbed_official 5:3762170b6d4d 351 /**
mbed_official 5:3762170b6d4d 352 * @} end of RealFFT group
mbed_official 5:3762170b6d4d 353 */