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# arm_fir_q31.c

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    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_q31.c
    00009 *
    00010 * Description:  Q31 FIR filter processing function.
    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 0.0.5  2010/04/26
    00027 *    incorporated review comments and updated with latest CMSIS layer
    00028 *
    00029 * Version 0.0.3  2010/03/10
    00030 *    Initial version
    00031 * -------------------------------------------------------------------- */
    00032
    00033 #include "arm_math.h"
    00034
    00064 void arm_fir_q31(
    00065   const arm_fir_instance_q31 * S,
    00066   q31_t * pSrc,
    00067   q31_t * pDst,
    00068   uint32_t blockSize)
    00069 {
    00070   q31_t *pState = S->pState;                     /* State pointer */
    00071   q31_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
    00072   q31_t *pStateCurnt;                            /* Points to the current sample of the state */
    00073   q31_t x0, x1, x2, x3;                          /* Temporary variables to hold state */
    00074   q31_t c0;                                      /* Temporary variable to hold coefficient value */
    00075   q31_t *px;                                     /* Temporary pointer for state */
    00076   q31_t *pb;                                     /* Temporary pointer for coefficient buffer */
    00077   q63_t acc0, acc1, acc2, acc3;                  /* Accumulators */
    00078   uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
    00079   uint32_t i, tapCnt, blkCnt;                    /* Loop counters */
    00080
    00081   /* S->pState points to state array which contains previous frame (numTaps - 1) samples */
    00082   /* pStateCurnt points to the location where the new input data should be written */
    00083   pStateCurnt = &(S->pState[(numTaps - 1u)]);
    00084
    00085   /* Apply loop unrolling and compute 4 output values simultaneously.
    00086    * The variables acc0 ... acc3 hold output values that are being computed:
    00087    *
    00088    *    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]
    00089    *    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]
    00090    *    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]
    00091    *    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]
    00092    */
    00093   blkCnt = blockSize >> 2;
    00094
    00095   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00096    ** a second loop below computes the remaining 1 to 3 samples. */
    00097   while(blkCnt > 0u)
    00098   {
    00099     /* Copy four new input samples into the state buffer */
    00100     *pStateCurnt++ = *pSrc++;
    00101     *pStateCurnt++ = *pSrc++;
    00102     *pStateCurnt++ = *pSrc++;
    00103     *pStateCurnt++ = *pSrc++;
    00104
    00105     /* Set all accumulators to zero */
    00106     acc0 = 0;
    00107     acc1 = 0;
    00108     acc2 = 0;
    00109     acc3 = 0;
    00110
    00111     /* Initialize state pointer */
    00112     px = pState;
    00113
    00114     /* Initialize coefficient pointer */
    00115     pb = pCoeffs;
    00116
    00117     /* Read the first three samples from the state buffer:
    00118      *  x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */
    00119     x0 = *(px++);
    00120     x1 = *(px++);
    00121     x2 = *(px++);
    00122
    00123     /* Loop unrolling.  Process 4 taps at a time. */
    00124     tapCnt = numTaps >> 2;
    00125     i = tapCnt;
    00126
    00127     while(i > 0u)
    00128     {
    00129       /* Read the b[numTaps] coefficient */
    00130       c0 = *(pb++);
    00131
    00132       /* Read x[n-numTaps-3] sample */
    00133       x3 = *(px++);
    00134
    00135       /* acc0 +=  b[numTaps] * x[n-numTaps] */
    00136       acc0 += ((q63_t) x0 * c0);
    00137
    00138       /* acc1 +=  b[numTaps] * x[n-numTaps-1] */
    00139       acc1 += ((q63_t) x1 * c0);
    00140
    00141       /* acc2 +=  b[numTaps] * x[n-numTaps-2] */
    00142       acc2 += ((q63_t) x2 * c0);
    00143
    00144       /* acc3 +=  b[numTaps] * x[n-numTaps-3] */
    00145       acc3 += ((q63_t) x3 * c0);
    00146
    00147       /* Read the b[numTaps-1] coefficient */
    00148       c0 = *(pb++);
    00149
    00150       /* Read x[n-numTaps-4] sample */
    00151       x0 = *(px++);
    00152
    00153       /* Perform the multiply-accumulates */
    00154       acc0 += ((q63_t) x1 * c0);
    00155       acc1 += ((q63_t) x2 * c0);
    00156       acc2 += ((q63_t) x3 * c0);
    00157       acc3 += ((q63_t) x0 * c0);
    00158
    00159       /* Read the b[numTaps-2] coefficient */
    00160       c0 = *(pb++);
    00161
    00162       /* Read x[n-numTaps-5] sample */
    00163       x1 = *(px++);
    00164
    00165       /* Perform the multiply-accumulates */
    00166       acc0 += ((q63_t) x2 * c0);
    00167       acc1 += ((q63_t) x3 * c0);
    00168       acc2 += ((q63_t) x0 * c0);
    00169       acc3 += ((q63_t) x1 * c0);
    00170       /* Read the b[numTaps-3] coefficients */
    00171       c0 = *(pb++);
    00172
    00173       /* Read x[n-numTaps-6] sample */
    00174       x2 = *(px++);
    00175
    00176       /* Perform the multiply-accumulates */
    00177       acc0 += ((q63_t) x3 * c0);
    00178       acc1 += ((q63_t) x0 * c0);
    00179       acc2 += ((q63_t) x1 * c0);
    00180       acc3 += ((q63_t) x2 * c0);
    00181       i--;
    00182     }
    00183
    00184     /* If the filter length is not a multiple of 4, compute the remaining filter taps */
    00185
    00186     i = numTaps - (tapCnt * 4u);
    00187     while(i > 0u)
    00188     {
    00189       /* Read coefficients */
    00190       c0 = *(pb++);
    00191
    00192       /* Fetch 1 state variable */
    00193       x3 = *(px++);
    00194
    00195       /* Perform the multiply-accumulates */
    00196       acc0 += ((q63_t) x0 * c0);
    00197       acc1 += ((q63_t) x1 * c0);
    00198       acc2 += ((q63_t) x2 * c0);
    00199       acc3 += ((q63_t) x3 * c0);
    00200
    00201       /* Reuse the present sample states for next sample */
    00202       x0 = x1;
    00203       x1 = x2;
    00204       x2 = x3;
    00205
    00206       /* Decrement the loop counter */
    00207       i--;
    00208     }
    00209
    00210     /* Advance the state pointer by 4 to process the next group of 4 samples */
    00211     pState = pState + 4;
    00212
    00213     /* The results in the 4 accumulators are in 2.30 format.  Convert to 1.31
    00214      ** Then store the 4 outputs in the destination buffer. */
    00215     *pDst++ = (q31_t) (acc0 >> 31u);
    00216     *pDst++ = (q31_t) (acc1 >> 31u);
    00217     *pDst++ = (q31_t) (acc2 >> 31u);
    00218     *pDst++ = (q31_t) (acc3 >> 31u);
    00219
    00220     /* Decrement the samples loop counter */
    00221     blkCnt--;
    00222   }
    00223
    00224
    00225   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00226    ** No loop unrolling is used. */
    00227   blkCnt = blockSize % 4u;
    00228
    00229   while(blkCnt > 0u)
    00230   {
    00231     /* Copy one sample at a time into state buffer */
    00232     *pStateCurnt++ = *pSrc++;
    00233
    00234     /* Set the accumulator to zero */
    00235     acc0 = 0;
    00236
    00237     /* Initialize state pointer */
    00238     px = pState;
    00239
    00240     /* Initialize Coefficient pointer */
    00241     pb = (pCoeffs);
    00242
    00243     i = numTaps;
    00244
    00245     /* Perform the multiply-accumulates */
    00246     do
    00247     {
    00248       acc0 += (q63_t) * (px++) * (*(pb++));
    00249       i--;
    00250     } while(i > 0u);
    00251
    00252     /* The result is in 2.62 format.  Convert to 1.31
    00253      ** Then store the output in the destination buffer. */
    00254     *pDst++ = (q31_t) (acc0 >> 31u);
    00255
    00256     /* Advance state pointer by 1 for the next sample */
    00257     pState = pState + 1;
    00258
    00259     /* Decrement the samples loop counter */
    00260     blkCnt--;
    00261   }
    00262
    00263   /* Processing is complete.
    00264    ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
    00265    ** This prepares the state buffer for the next function call. */
    00266
    00267   /* Points to the start of the state buffer */
    00268   pStateCurnt = S->pState;
    00269
    00270   tapCnt = (numTaps - 1u) >> 2u;
    00271
    00272   /* copy data */
    00273   while(tapCnt > 0u)
    00274   {
    00275     *pStateCurnt++ = *pState++;
    00276     *pStateCurnt++ = *pState++;
    00277     *pStateCurnt++ = *pState++;
    00278     *pStateCurnt++ = *pState++;
    00279
    00280     /* Decrement the loop counter */
    00281     tapCnt--;
    00282   }
    00283
    00284   /* Calculate remaining number of copies */
    00285   tapCnt = (numTaps - 1u) % 0x4u;
    00286
    00287   /* Copy the remaining q31_t data */
    00288   while(tapCnt > 0u)
    00289   {
    00290     *pStateCurnt++ = *pState++;
    00291
    00292     /* Decrement the loop counter */
    00293     tapCnt--;
    00294   }
    00295
    00296 }
    00297

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