- Main Page
- Modules
- Data Structures
- Files
- Examples

- File List
- Globals

# 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:        15. July 2011
    00005 * $Revision:    V1.0.10
    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/Cortex-M0
    00013 *
    00014 * Version 1.0.10 2011/7/15
    00015 *    Big Endian support added and Merged M0 and M3/M4 Source code.
    00016 *
    00017 * Version 1.0.3 2010/11/29
    00018 *    Re-organized the CMSIS folders and updated documentation.
    00019 *
    00020 * Version 1.0.2 2010/11/11
    00021 *    Documentation updated.
    00022 *
    00023 * Version 1.0.1 2010/10/05
    00024 *    Production release and review comments incorporated.
    00025 *
    00026 * Version 1.0.0 2010/09/20
    00027 *    Production release and review comments incorporated
    00028 *
    00029 * Version 0.0.7  2010/06/10
    00030 *    Misra-C changes done
    00031 *
    00032 * -------------------------------------------------------------------- */
    00033
    00034 #include "arm_math.h"
    00035
    00132 void arm_fir_decimate_f32(
    00133   const arm_fir_decimate_instance_f32 * S,
    00134   float32_t * pSrc,
    00135   float32_t * pDst,
    00136   uint32_t blockSize)
    00137 {
    00138   float32_t *pState = S->pState;                 /* State pointer */
    00139   float32_t *pCoeffs = S->pCoeffs;               /* Coefficient pointer */
    00140   float32_t *pStateCurnt;                        /* Points to the current sample of the state */
    00141   float32_t *px, *pb;                            /* Temporary pointers for state and coefficient buffers */
    00142   float32_t sum0;                                /* Accumulator */
    00143   float32_t x0, c0;                              /* Temporary variables to hold state and coefficient values */
    00144   uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
    00145   uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M;  /* Loop counters */
    00146
    00147 #ifndef ARM_MATH_CM0
    00148
    00149   /* Run the below code for Cortex-M4 and Cortex-M3 */
    00150
    00151   /* S->pState buffer contains previous frame (numTaps - 1) samples */
    00152   /* pStateCurnt points to the location where the new input data should be written */
    00153   pStateCurnt = S->pState + (numTaps - 1u);
    00154
    00155   /* Total number of output samples to be computed */
    00156   blkCnt = outBlockSize;
    00157
    00158   while(blkCnt > 0u)
    00159   {
    00160     /* Copy decimation factor number of new input samples into the state buffer */
    00161     i = S->M;
    00162
    00163     do
    00164     {
    00165       *pStateCurnt++ = *pSrc++;
    00166
    00167     } while(--i);
    00168
    00169     /* Set accumulator to zero */
    00170     sum0 = 0.0f;
    00171
    00172     /* Initialize state pointer */
    00173     px = pState;
    00174
    00175     /* Initialize coeff pointer */
    00176     pb = pCoeffs;
    00177
    00178     /* Loop unrolling.  Process 4 taps at a time. */
    00179     tapCnt = numTaps >> 2;
    00180
    00181     /* Loop over the number of taps.  Unroll by a factor of 4.
    00182      ** Repeat until we've computed numTaps-4 coefficients. */
    00183     while(tapCnt > 0u)
    00184     {
    00185       /* Read the b[numTaps-1] coefficient */
    00186       c0 = *(pb++);
    00187
    00188       /* Read x[n-numTaps-1] sample */
    00189       x0 = *(px++);
    00190
    00191       /* Perform the multiply-accumulate */
    00192       sum0 += x0 * c0;
    00193
    00194       /* Read the b[numTaps-2] coefficient */
    00195       c0 = *(pb++);
    00196
    00197       /* Read x[n-numTaps-2] sample */
    00198       x0 = *(px++);
    00199
    00200       /* Perform the multiply-accumulate */
    00201       sum0 += x0 * c0;
    00202
    00203       /* Read the b[numTaps-3] coefficient */
    00204       c0 = *(pb++);
    00205
    00206       /* Read x[n-numTaps-3] sample */
    00207       x0 = *(px++);
    00208
    00209       /* Perform the multiply-accumulate */
    00210       sum0 += x0 * c0;
    00211
    00212       /* Read the b[numTaps-4] coefficient */
    00213       c0 = *(pb++);
    00214
    00215       /* Read x[n-numTaps-4] sample */
    00216       x0 = *(px++);
    00217
    00218       /* Perform the multiply-accumulate */
    00219       sum0 += x0 * c0;
    00220
    00221       /* Decrement the loop counter */
    00222       tapCnt--;
    00223     }
    00224
    00225     /* If the filter length is not a multiple of 4, compute the remaining filter taps */
    00226     tapCnt = numTaps % 0x4u;
    00227
    00228     while(tapCnt > 0u)
    00229     {
    00230       /* Read coefficients */
    00231       c0 = *(pb++);
    00232
    00233       /* Fetch 1 state variable */
    00234       x0 = *(px++);
    00235
    00236       /* Perform the multiply-accumulate */
    00237       sum0 += x0 * c0;
    00238
    00239       /* Decrement the loop counter */
    00240       tapCnt--;
    00241     }
    00242
    00243     /* Advance the state pointer by the decimation factor
    00244      * to process the next group of decimation factor number samples */
    00245     pState = pState + S->M;
    00246
    00247     /* The result is in the accumulator, store in the destination buffer. */
    00248     *pDst++ = sum0;
    00249
    00250     /* Decrement the loop counter */
    00251     blkCnt--;
    00252   }
    00253
    00254   /* Processing is complete.
    00255    ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
    00256    ** This prepares the state buffer for the next function call. */
    00257
    00258   /* Points to the start of the state buffer */
    00259   pStateCurnt = S->pState;
    00260
    00261   i = (numTaps - 1u) >> 2;
    00262
    00263   /* copy data */
    00264   while(i > 0u)
    00265   {
    00266     *pStateCurnt++ = *pState++;
    00267     *pStateCurnt++ = *pState++;
    00268     *pStateCurnt++ = *pState++;
    00269     *pStateCurnt++ = *pState++;
    00270
    00271     /* Decrement the loop counter */
    00272     i--;
    00273   }
    00274
    00275   i = (numTaps - 1u) % 0x04u;
    00276
    00277   /* copy data */
    00278   while(i > 0u)
    00279   {
    00280     *pStateCurnt++ = *pState++;
    00281
    00282     /* Decrement the loop counter */
    00283     i--;
    00284   }
    00285
    00286 #else
    00287
    00288 /* Run the below code for Cortex-M0 */
    00289
    00290   /* S->pState buffer contains previous frame (numTaps - 1) samples */
    00291   /* pStateCurnt points to the location where the new input data should be written */
    00292   pStateCurnt = S->pState + (numTaps - 1u);
    00293
    00294   /* Total number of output samples to be computed */
    00295   blkCnt = outBlockSize;
    00296
    00297   while(blkCnt > 0u)
    00298   {
    00299     /* Copy decimation factor number of new input samples into the state buffer */
    00300     i = S->M;
    00301
    00302     do
    00303     {
    00304       *pStateCurnt++ = *pSrc++;
    00305
    00306     } while(--i);
    00307
    00308     /* Set accumulator to zero */
    00309     sum0 = 0.0f;
    00310
    00311     /* Initialize state pointer */
    00312     px = pState;
    00313
    00314     /* Initialize coeff pointer */
    00315     pb = pCoeffs;
    00316
    00317     tapCnt = numTaps;
    00318
    00319     while(tapCnt > 0u)
    00320     {
    00321       /* Read coefficients */
    00322       c0 = *pb++;
    00323
    00324       /* Fetch 1 state variable */
    00325       x0 = *px++;
    00326
    00327       /* Perform the multiply-accumulate */
    00328       sum0 += x0 * c0;
    00329
    00330       /* Decrement the loop counter */
    00331       tapCnt--;
    00332     }
    00333
    00334     /* Advance the state pointer by the decimation factor
    00335      * to process the next group of decimation factor number samples */
    00336     pState = pState + S->M;
    00337
    00338     /* The result is in the accumulator, store in the destination buffer. */
    00339     *pDst++ = sum0;
    00340
    00341     /* Decrement the loop counter */
    00342     blkCnt--;
    00343   }
    00344
    00345   /* Processing is complete.
    00346    ** Now copy the last numTaps - 1 samples to the start of the state buffer.
    00347    ** This prepares the state buffer for the next function call. */
    00348
    00349   /* Points to the start of the state buffer */
    00350   pStateCurnt = S->pState;
    00351
    00352   /* Copy numTaps number of values */
    00353   i = (numTaps - 1u);
    00354
    00355   /* copy data */
    00356   while(i > 0u)
    00357   {
    00358     *pStateCurnt++ = *pState++;
    00359
    00360     /* Decrement the loop counter */
    00361     i--;
    00362   }
    00363
    00364 #endif /*   #ifndef ARM_MATH_CM0        */
    00365
    00366 }
    00367

All Data Structures Files Functions Variables Typedefs Enumerations Enumerator Defines