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# arm_fir_f32.c

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    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_f32.c
    00009 *
    00010 * Description:  Floating-point FIR filter processing function.
    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 0.0.5  2010/04/26
    00030 *    incorporated review comments and updated with latest CMSIS layer
    00031 *
    00032 * Version 0.0.3  2010/03/10
    00033 *    Initial version
    00034 * -------------------------------------------------------------------- */
    00035
    00036 #include "arm_math.h"
    00037
    00128 void arm_fir_f32(
    00129   const arm_fir_instance_f32 * S,
    00130   float32_t * pSrc,
    00131   float32_t * pDst,
    00132   uint32_t blockSize)
    00133 {
    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   uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
    00140   uint32_t i, tapCnt, blkCnt;                    /* Loop counters */
    00141
    00142
    00143 #ifndef ARM_MATH_CM0
    00144
    00145   /* Run the below code for Cortex-M4 and Cortex-M3 */
    00146
    00147   float32_t acc0, acc1, acc2, acc3;              /* Accumulators */
    00148   float32_t x0, x1, x2, x3, c0;                  /* Temporary variables to hold state and coefficient values */
    00149
    00150
    00151   /* S->pState points to state array which 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   /* Apply loop unrolling and compute 4 output values simultaneously.
    00156    * The variables acc0 ... acc3 hold output values that are being computed:
    00157    *
    00158    *    acc0 =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0]
    00159    *    acc1 =  b[numTaps-1] * x[n-numTaps] +   b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1]
    00160    *    acc2 =  b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] +   b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2]
    00161    *    acc3 =  b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps]   +...+ b[0] * x[3]
    00162    */
    00163   blkCnt = blockSize >> 2;
    00164
    00165   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00166    ** a second loop below computes the remaining 1 to 3 samples. */
    00167   while(blkCnt > 0u)
    00168   {
    00169     /* Copy four new input samples into the state buffer */
    00170     *pStateCurnt++ = *pSrc++;
    00171     *pStateCurnt++ = *pSrc++;
    00172     *pStateCurnt++ = *pSrc++;
    00173     *pStateCurnt++ = *pSrc++;
    00174
    00175     /* Set all accumulators to zero */
    00176     acc0 = 0.0f;
    00177     acc1 = 0.0f;
    00178     acc2 = 0.0f;
    00179     acc3 = 0.0f;
    00180
    00181     /* Initialize state pointer */
    00182     px = pState;
    00183
    00184     /* Initialize coeff pointer */
    00185     pb = (pCoeffs);
    00186
    00187     /* Read the first three samples from the state buffer:  x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */
    00188     x0 = *px++;
    00189     x1 = *px++;
    00190     x2 = *px++;
    00191
    00192     /* Loop unrolling.  Process 4 taps at a time. */
    00193     tapCnt = numTaps >> 2u;
    00194
    00195     /* Loop over the number of taps.  Unroll by a factor of 4.
    00196      ** Repeat until we've computed numTaps-4 coefficients. */
    00197     while(tapCnt > 0u)
    00198     {
    00199       /* Read the b[numTaps-1] coefficient */
    00200       c0 = *(pb++);
    00201
    00202       /* Read x[n-numTaps-3] sample */
    00203       x3 = *(px++);
    00204
    00205       /* acc0 +=  b[numTaps-1] * x[n-numTaps] */
    00206       acc0 += x0 * c0;
    00207
    00208       /* acc1 +=  b[numTaps-1] * x[n-numTaps-1] */
    00209       acc1 += x1 * c0;
    00210
    00211       /* acc2 +=  b[numTaps-1] * x[n-numTaps-2] */
    00212       acc2 += x2 * c0;
    00213
    00214       /* acc3 +=  b[numTaps-1] * x[n-numTaps-3] */
    00215       acc3 += x3 * c0;
    00216
    00217       /* Read the b[numTaps-2] coefficient */
    00218       c0 = *(pb++);
    00219
    00220       /* Read x[n-numTaps-4] sample */
    00221       x0 = *(px++);
    00222
    00223       /* Perform the multiply-accumulate */
    00224       acc0 += x1 * c0;
    00225       acc1 += x2 * c0;
    00226       acc2 += x3 * c0;
    00227       acc3 += x0 * c0;
    00228
    00229       /* Read the b[numTaps-3] coefficient */
    00230       c0 = *(pb++);
    00231
    00232       /* Read x[n-numTaps-5] sample */
    00233       x1 = *(px++);
    00234
    00235       /* Perform the multiply-accumulates */
    00236       acc0 += x2 * c0;
    00237       acc1 += x3 * c0;
    00238       acc2 += x0 * c0;
    00239       acc3 += x1 * c0;
    00240
    00241       /* Read the b[numTaps-4] coefficient */
    00242       c0 = *(pb++);
    00243
    00244       /* Read x[n-numTaps-6] sample */
    00245       x2 = *(px++);
    00246
    00247       /* Perform the multiply-accumulates */
    00248       acc0 += x3 * c0;
    00249       acc1 += x0 * c0;
    00250       acc2 += x1 * c0;
    00251       acc3 += x2 * c0;
    00252
    00253       tapCnt--;
    00254     }
    00255
    00256     /* If the filter length is not a multiple of 4, compute the remaining filter taps */
    00257     tapCnt = numTaps % 0x4u;
    00258
    00259     while(tapCnt > 0u)
    00260     {
    00261       /* Read coefficients */
    00262       c0 = *(pb++);
    00263
    00264       /* Fetch 1 state variable */
    00265       x3 = *(px++);
    00266
    00267       /* Perform the multiply-accumulates */
    00268       acc0 += x0 * c0;
    00269       acc1 += x1 * c0;
    00270       acc2 += x2 * c0;
    00271       acc3 += x3 * c0;
    00272
    00273       /* Reuse the present sample states for next sample */
    00274       x0 = x1;
    00275       x1 = x2;
    00276       x2 = x3;
    00277
    00278       /* Decrement the loop counter */
    00279       tapCnt--;
    00280     }
    00281
    00282     /* Advance the state pointer by 4 to process the next group of 4 samples */
    00283     pState = pState + 4;
    00284
    00285     /* The results in the 4 accumulators, store in the destination buffer. */
    00286     *pDst++ = acc0;
    00287     *pDst++ = acc1;
    00288     *pDst++ = acc2;
    00289     *pDst++ = acc3;
    00290
    00291     blkCnt--;
    00292   }
    00293
    00294   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00295    ** No loop unrolling is used. */
    00296   blkCnt = blockSize % 0x4u;
    00297
    00298   while(blkCnt > 0u)
    00299   {
    00300     /* Copy one sample at a time into state buffer */
    00301     *pStateCurnt++ = *pSrc++;
    00302
    00303     /* Set the accumulator to zero */
    00304     acc0 = 0.0f;
    00305
    00306     /* Initialize state pointer */
    00307     px = pState;
    00308
    00309     /* Initialize Coefficient pointer */
    00310     pb = (pCoeffs);
    00311
    00312     i = numTaps;
    00313
    00314     /* Perform the multiply-accumulates */
    00315     do
    00316     {
    00317       acc0 += *px++ * *pb++;
    00318       i--;
    00319
    00320     } while(i > 0u);
    00321
    00322     /* The result is store in the destination buffer. */
    00323     *pDst++ = acc0;
    00324
    00325     /* Advance state pointer by 1 for the next sample */
    00326     pState = pState + 1;
    00327
    00328     blkCnt--;
    00329   }
    00330
    00331   /* Processing is complete.
    00332    ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
    00333    ** This prepares the state buffer for the next function call. */
    00334
    00335   /* Points to the start of the state buffer */
    00336   pStateCurnt = S->pState;
    00337
    00338   tapCnt = (numTaps - 1u) >> 2u;
    00339
    00340   /* copy data */
    00341   while(tapCnt > 0u)
    00342   {
    00343     *pStateCurnt++ = *pState++;
    00344     *pStateCurnt++ = *pState++;
    00345     *pStateCurnt++ = *pState++;
    00346     *pStateCurnt++ = *pState++;
    00347
    00348     /* Decrement the loop counter */
    00349     tapCnt--;
    00350   }
    00351
    00352   /* Calculate remaining number of copies */
    00353   tapCnt = (numTaps - 1u) % 0x4u;
    00354
    00355   /* Copy the remaining q31_t data */
    00356   while(tapCnt > 0u)
    00357   {
    00358     *pStateCurnt++ = *pState++;
    00359
    00360     /* Decrement the loop counter */
    00361     tapCnt--;
    00362   }
    00363
    00364 #else
    00365
    00366   /* Run the below code for Cortex-M0 */
    00367
    00368   float32_t acc;
    00369
    00370   /* S->pState points to state array which contains previous frame (numTaps - 1) samples */
    00371   /* pStateCurnt points to the location where the new input data should be written */
    00372   pStateCurnt = &(S->pState[(numTaps - 1u)]);
    00373
    00374   /* Initialize blkCnt with blockSize */
    00375   blkCnt = blockSize;
    00376
    00377   while(blkCnt > 0u)
    00378   {
    00379     /* Copy one sample at a time into state buffer */
    00380     *pStateCurnt++ = *pSrc++;
    00381
    00382     /* Set the accumulator to zero */
    00383     acc = 0.0f;
    00384
    00385     /* Initialize state pointer */
    00386     px = pState;
    00387
    00388     /* Initialize Coefficient pointer */
    00389     pb = pCoeffs;
    00390
    00391     i = numTaps;
    00392
    00393     /* Perform the multiply-accumulates */
    00394     do
    00395     {
    00396       /* acc =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0] */
    00397       acc += *px++ * *pb++;
    00398       i--;
    00399
    00400     } while(i > 0u);
    00401
    00402     /* The result is store in the destination buffer. */
    00403     *pDst++ = acc;
    00404
    00405     /* Advance state pointer by 1 for the next sample */
    00406     pState = pState + 1;
    00407
    00408     blkCnt--;
    00409   }
    00410
    00411   /* Processing is complete.
    00412    ** Now copy the last numTaps - 1 samples to the starting of the state buffer.
    00413    ** This prepares the state buffer for the next function call. */
    00414
    00415   /* Points to the start of the state buffer */
    00416   pStateCurnt = S->pState;
    00417
    00418   /* Copy numTaps number of values */
    00419   tapCnt = numTaps - 1u;
    00420
    00421   /* Copy data */
    00422   while(tapCnt > 0u)
    00423   {
    00424     *pStateCurnt++ = *pState++;
    00425
    00426     /* Decrement the loop counter */
    00427     tapCnt--;
    00428   }
    00429
    00430 #endif /*   #ifndef ARM_MATH_CM0 */
    00431
    00432 }
    00433

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