CMSIS DSP Software Library: arm_dct4_f32.c Source File
Main Page
Modules
Data Structures
Files
Examples
File List
Globals
arm_dct4_f32.c
Go to the documentation of this file.00001 /* ----------------------------------------------------------------------
00002 * Copyright (C) 2010 ARM Limited. All rights reserved.
00003 *
00004 * $Date: 29. November 2010
00005 * $Revision: V1.0.3
00006 *
00007 * Project: CMSIS DSP Library
00008 * Title: arm_dct4_f32.c
00009 *
00010 * Description: Processing function of DCT4 & IDCT4 F32.
00011 *
00012 * Target Processor: Cortex-M4/Cortex-M3
00013 *
00014 * Version 1.0.3 2010/11/29
00015 * Re-organized the CMSIS folders and updated documentation.
00016 *
00017 * Version 1.0.2 2010/11/11
00018 * Documentation updated.
00019 *
00020 * Version 1.0.1 2010/10/05
00021 * Production release and review comments incorporated.
00022 *
00023 * Version 1.0.0 2010/09/20
00024 * Production release and review comments incorporated.
00025 * -------------------------------------------------------------------- */
00026
00027 #include "arm_math.h"
00028
00123 void arm_dct4_f32(
00124 const arm_dct4_instance_f32 * S,
00125 float32_t * pState,
00126 float32_t * pInlineBuffer)
00127 {
00128 uint32_t i; /* Loop counter */
00129 float32_t *weights = S->pTwiddle; /* Pointer to the Weights table */
00130 float32_t *cosFact = S->pCosFactor; /* Pointer to the cos factors table */
00131 float32_t *pS1, *pS2, *pbuff; /* Temporary pointers for input buffer and pState buffer */
00132 float32_t in; /* Temporary variable */
00133
00134
00135 /* DCT4 computation involves DCT2 (which is calculated using RFFT)
00136 * along with some pre-processing and post-processing.
00137 * Computational procedure is explained as follows:
00138 * (a) Pre-processing involves multiplying input with cos factor,
00139 * r(n) = 2 * u(n) * cos(pi*(2*n+1)/(4*n))
00140 * where,
00141 * r(n) -- output of preprocessing
00142 * u(n) -- input to preprocessing(actual Source buffer)
00143 * (b) Calculation of DCT2 using FFT is divided into three steps:
00144 * Step1: Re-ordering of even and odd elements of input.
00145 * Step2: Calculating FFT of the re-ordered input.
00146 * Step3: Taking the real part of the product of FFT output and weights.
00147 * (c) Post-processing - DCT4 can be obtained from DCT2 output using the following equation:
00148 * Y4(k) = Y2(k) - Y4(k-1) and Y4(-1) = Y4(0)
00149 * where,
00150 * Y4 -- DCT4 output, Y2 -- DCT2 output
00151 * (d) Multiplying the output with the normalizing factor sqrt(2/N).
00152 */
00153
00154 /*-------- Pre-processing ------------*/
00155 /* Multiplying input with cos factor i.e. r(n) = 2 * x(n) * cos(pi*(2*n+1)/(4*n)) */
00156 arm_scale_f32(pInlineBuffer, 2.0f, pInlineBuffer, S->N);
00157 arm_mult_f32(pInlineBuffer, cosFact, pInlineBuffer, S->N);
00158
00159 /* ----------------------------------------------------------------
00160 * Step1: Re-ordering of even and odd elements as,
00161 * pState[i] = pInlineBuffer[2*i] and
00162 * pState[N-i-1] = pInlineBuffer[2*i+1] where i = 0 to N/2
00163 ---------------------------------------------------------------------*/
00164
00165 /* pS1 initialized to pState */
00166 pS1 = pState;
00167
00168 /* pS2 initialized to pState+N-1, so that it points to the end of the state buffer */
00169 pS2 = pState + (S->N - 1u);
00170
00171 /* pbuff initialized to input buffer */
00172 pbuff = pInlineBuffer;
00173
00174 /* Initializing the loop counter to N/2 >> 2 for loop unrolling by 4 */
00175 i = (uint32_t) S->Nby2 >> 2u;
00176
00177 /* First part of the processing with loop unrolling. Compute 4 outputs at a time.
00178 ** a second loop below computes the remaining 1 to 3 samples. */
00179 do
00180 {
00181 /* Re-ordering of even and odd elements */
00182 /* pState[i] = pInlineBuffer[2*i] */
00183 *pS1++ = *pbuff++;
00184 /* pState[N-i-1] = pInlineBuffer[2*i+1] */
00185 *pS2-- = *pbuff++;
00186
00187 *pS1++ = *pbuff++;
00188 *pS2-- = *pbuff++;
00189
00190 *pS1++ = *pbuff++;
00191 *pS2-- = *pbuff++;
00192
00193 *pS1++ = *pbuff++;
00194 *pS2-- = *pbuff++;
00195
00196 /* Decrement the loop counter */
00197 i--;
00198 } while(i > 0u);
00199
00200 /* pbuff initialized to input buffer */
00201 pbuff = pInlineBuffer;
00202
00203 /* pS1 initialized to pState */
00204 pS1 = pState;
00205
00206 /* Initializing the loop counter to N/4 instead of N for loop unrolling */
00207 i = (uint32_t) S->N >> 2u;
00208
00209 /* Processing with loop unrolling 4 times as N is always multiple of 4.
00210 * Compute 4 outputs at a time */
00211 do
00212 {
00213 /* Writing the re-ordered output back to inplace input buffer */
00214 *pbuff++ = *pS1++;
00215 *pbuff++ = *pS1++;
00216 *pbuff++ = *pS1++;
00217 *pbuff++ = *pS1++;
00218
00219 /* Decrement the loop counter */
00220 i--;
00221 } while(i > 0u);
00222
00223
00224 /* ---------------------------------------------------------
00225 * Step2: Calculate RFFT for N-point input
00226 * ---------------------------------------------------------- */
00227 /* pInlineBuffer is real input of length N , pState is the complex output of length 2N */
00228 arm_rfft_f32(S->pRfft, pInlineBuffer, pState);
00229
00230 /*----------------------------------------------------------------------
00231 * Step3: Multiply the FFT output with the weights.
00232 *----------------------------------------------------------------------*/
00233 arm_cmplx_mult_cmplx_f32(pState, weights, pState, S->N);
00234
00235 /* ----------- Post-processing ---------- */
00236 /* DCT-IV can be obtained from DCT-II by the equation,
00237 * Y4(k) = Y2(k) - Y4(k-1) and Y4(-1) = Y4(0)
00238 * Hence, Y4(0) = Y2(0)/2 */
00239 /* Getting only real part from the output and Converting to DCT-IV */
00240
00241 /* Initializing the loop counter to N >> 2 for loop unrolling by 4 */
00242 i = ((uint32_t) S->N - 1u) >> 2u;
00243
00244 /* pbuff initialized to input buffer. */
00245 pbuff = pInlineBuffer;
00246
00247 /* pS1 initialized to pState */
00248 pS1 = pState;
00249
00250 /* Calculating Y4(0) from Y2(0) using Y4(0) = Y2(0)/2 */
00251 in = *pS1++ * (float32_t) 0.5;
00252 /* input buffer acts as inplace, so output values are stored in the input itself. */
00253 *pbuff++ = in;
00254
00255 /* pState pointer is incremented twice as the real values are located alternatively in the array */
00256 pS1++;
00257
00258 /* First part of the processing with loop unrolling. Compute 4 outputs at a time.
00259 ** a second loop below computes the remaining 1 to 3 samples. */
00260 do
00261 {
00262 /* Calculating Y4(1) to Y4(N-1) from Y2 using equation Y4(k) = Y2(k) - Y4(k-1) */
00263 /* pState pointer (pS1) is incremented twice as the real values are located alternatively in the array */
00264 in = *pS1++ - in;
00265 *pbuff++ = in;
00266 /* points to the next real value */
00267 pS1++;
00268
00269 in = *pS1++ - in;
00270 *pbuff++ = in;
00271 pS1++;
00272
00273 in = *pS1++ - in;
00274 *pbuff++ = in;
00275 pS1++;
00276
00277 in = *pS1++ - in;
00278 *pbuff++ = in;
00279 pS1++;
00280
00281 /* Decrement the loop counter */
00282 i--;
00283 } while(i > 0u);
00284
00285 /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
00286 ** No loop unrolling is used. */
00287 i = ((uint32_t) S->N - 1u) % 0x4u;
00288
00289 while(i > 0u)
00290 {
00291 /* Calculating Y4(1) to Y4(N-1) from Y2 using equation Y4(k) = Y2(k) - Y4(k-1) */
00292 /* pState pointer (pS1) is incremented twice as the real values are located alternatively in the array */
00293 in = *pS1++ - in;
00294 *pbuff++ = in;
00295 /* points to the next real value */
00296 pS1++;
00297
00298 /* Decrement the loop counter */
00299 i--;
00300 }
00301
00302
00303 /*------------ Normalizing the output by multiplying with the normalizing factor ----------*/
00304
00305 /* Initializing the loop counter to N/4 instead of N for loop unrolling */
00306 i = (uint32_t) S->N >> 2u;
00307
00308 /* pbuff initialized to the pInlineBuffer(now contains the output values) */
00309 pbuff = pInlineBuffer;
00310
00311 /* Processing with loop unrolling 4 times as N is always multiple of 4. Compute 4 outputs at a time */
00312 do
00313 {
00314 /* Multiplying pInlineBuffer with the normalizing factor sqrt(2/N) */
00315 in = *pbuff;
00316 *pbuff++ = in * S->normalize;
00317
00318 in = *pbuff;
00319 *pbuff++ = in * S->normalize;
00320
00321 in = *pbuff;
00322 *pbuff++ = in * S->normalize;
00323
00324 in = *pbuff;
00325 *pbuff++ = in * S->normalize;
00326
00327 /* Decrement the loop counter */
00328 i--;
00329 } while(i > 0u);
00330
00331 }
00332
All Data Structures Files Functions Variables Typedefs Enumerations Enumerator Defines
Generated on Mon Nov 29 2010 17:19:56 for CMSIS DSP Software Library by
1.7.2