CMSIS DSP Software Library: arm_fir_decimate_f32.c Source File
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arm_fir_decimate_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_fir_decimate_f32.c
00009 *
00010 * Description: FIR decimation for floating-point sequences.
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 * Version 0.0.7 2010/06/10
00027 * Misra-C changes done
00028 *
00029 * -------------------------------------------------------------------- */
00030
00031 #include "arm_math.h"
00032
00129 void arm_fir_decimate_f32(
00130 const arm_fir_decimate_instance_f32 * S,
00131 float32_t * pSrc,
00132 float32_t * pDst,
00133 uint32_t blockSize)
00134 {
00135 float32_t *pState = S->pState; /* State pointer */
00136 float32_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
00137 float32_t *pStateCurnt; /* Points to the current sample of the state */
00138 float32_t *px, *pb; /* Temporary pointers for state and coefficient buffers */
00139 float32_t sum0; /* Accumulator */
00140 float32_t x0, c0; /* Temporary variables to hold state and coefficient values */
00141 uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */
00142 uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */
00143
00144 /* S->pState buffer contains previous frame (numTaps - 1) samples */
00145 /* pStateCurnt points to the location where the new input data should be written */
00146 pStateCurnt = S->pState + (numTaps - 1u);
00147
00148 /* Total number of output samples to be computed */
00149 blkCnt = outBlockSize;
00150
00151 while(blkCnt > 0u)
00152 {
00153 /* Copy decimation factor number of new input samples into the state buffer */
00154 i = S->M;
00155
00156 do
00157 {
00158 *pStateCurnt++ = *pSrc++;
00159
00160 } while(--i);
00161
00162 /* Set accumulator to zero */
00163 sum0 = 0.0f;
00164
00165 /* Initialize state pointer */
00166 px = pState;
00167
00168 /* Initialize coeff pointer */
00169 pb = pCoeffs;
00170
00171 /* Loop unrolling. Process 4 taps at a time. */
00172 tapCnt = numTaps >> 2;
00173
00174 /* Loop over the number of taps. Unroll by a factor of 4.
00175 ** Repeat until we've computed numTaps-4 coefficients. */
00176 while(tapCnt > 0u)
00177 {
00178 /* Read the b[numTaps-1] coefficient */
00179 c0 = *(pb++);
00180
00181 /* Read x[n-numTaps-1] sample */
00182 x0 = *(px++);
00183
00184 /* Perform the multiply-accumulate */
00185 sum0 += x0 * c0;
00186
00187 /* Read the b[numTaps-2] coefficient */
00188 c0 = *(pb++);
00189
00190 /* Read x[n-numTaps-2] sample */
00191 x0 = *(px++);
00192
00193 /* Perform the multiply-accumulate */
00194 sum0 += x0 * c0;
00195
00196 /* Read the b[numTaps-3] coefficient */
00197 c0 = *(pb++);
00198
00199 /* Read x[n-numTaps-3] sample */
00200 x0 = *(px++);
00201
00202 /* Perform the multiply-accumulate */
00203 sum0 += x0 * c0;
00204
00205 /* Read the b[numTaps-4] coefficient */
00206 c0 = *(pb++);
00207
00208 /* Read x[n-numTaps-4] sample */
00209 x0 = *(px++);
00210
00211 /* Perform the multiply-accumulate */
00212 sum0 += x0 * c0;
00213
00214 /* Decrement the loop counter */
00215 tapCnt--;
00216 }
00217
00218 /* If the filter length is not a multiple of 4, compute the remaining filter taps */
00219 tapCnt = numTaps % 0x4u;
00220
00221 while(tapCnt > 0u)
00222 {
00223 /* Read coefficients */
00224 c0 = *(pb++);
00225
00226 /* Fetch 1 state variable */
00227 x0 = *(px++);
00228
00229 /* Perform the multiply-accumulate */
00230 sum0 += x0 * c0;
00231
00232 /* Decrement the loop counter */
00233 tapCnt--;
00234 }
00235
00236 /* Advance the state pointer by the decimation factor
00237 * to process the next group of decimation factor number samples */
00238 pState = pState + S->M;
00239
00240 /* The result is in the accumulator, store in the destination buffer. */
00241 *pDst++ = sum0;
00242
00243 /* Decrement the loop counter */
00244 blkCnt--;
00245 }
00246
00247 /* Processing is complete.
00248 ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
00249 ** This prepares the state buffer for the next function call. */
00250
00251 /* Points to the start of the state buffer */
00252 pStateCurnt = S->pState;
00253
00254 i = (numTaps - 1u) >> 2;
00255
00256 /* copy data */
00257 while(i > 0u)
00258 {
00259 *pStateCurnt++ = *pState++;
00260 *pStateCurnt++ = *pState++;
00261 *pStateCurnt++ = *pState++;
00262 *pStateCurnt++ = *pState++;
00263
00264 /* Decrement the loop counter */
00265 i--;
00266 }
00267
00268 i = (numTaps - 1u) % 0x04u;
00269
00270 /* copy data */
00271 while(i > 0u)
00272 {
00273 *pStateCurnt++ = *pState++;
00274
00275 /* Decrement the loop counter */
00276 i--;
00277 }
00278 }
00279
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