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# arm_fir_decimate_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_decimate_q31.c
    00009 *
    00010 * Description:  Q31 FIR Decimator.
    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 #include "arm_math.h"
    00031
    00061 void arm_fir_decimate_q31(
    00062   const arm_fir_decimate_instance_q31 * S,
    00063   q31_t * pSrc,
    00064   q31_t * pDst,
    00065   uint32_t blockSize)
    00066 {
    00067   q31_t *pState = S->pState;                     /* State pointer */
    00068   q31_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
    00069   q31_t *pStateCurnt;                            /* Points to the current sample of the state */
    00070   q31_t x0, c0;                                  /* Temporary variables to hold state and coefficient values */
    00071   q31_t *px;                                     /* Temporary pointers for state buffer */
    00072   q31_t *pb;                                     /* Temporary pointers for coefficient buffer */
    00073   q63_t sum0;                                    /* Accumulator */
    00074   uint32_t numTaps = S->numTaps;                 /* Number of taps */
    00075   uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M;  /* Loop counters */
    00076
    00077
    00078   /* S->pState buffer contains previous frame (numTaps - 1) samples */
    00079   /* pStateCurnt points to the location where the new input data should be written */
    00080   pStateCurnt = S->pState + (numTaps - 1u);
    00081
    00082   /* Total number of output samples to be computed */
    00083   blkCnt = outBlockSize;
    00084
    00085   while(blkCnt > 0u)
    00086   {
    00087     /* Copy decimation factor number of new input samples into the state buffer */
    00088     i = S->M;
    00089
    00090     do
    00091     {
    00092       *pStateCurnt++ = *pSrc++;
    00093
    00094     } while(--i);
    00095
    00096     /* Set accumulator to zero */
    00097     sum0 = 0;
    00098
    00099     /* Initialize state pointer */
    00100     px = pState;
    00101
    00102     /* Initialize coeff pointer */
    00103     pb = pCoeffs;
    00104
    00105     /* Loop unrolling.  Process 4 taps at a time. */
    00106     tapCnt = numTaps >> 2;
    00107
    00108     /* Loop over the number of taps.  Unroll by a factor of 4.
    00109      ** Repeat until we've computed numTaps-4 coefficients. */
    00110     while(tapCnt > 0u)
    00111     {
    00112       /* Read the b[numTaps-1] coefficient */
    00113       c0 = *(pb++);
    00114
    00115       /* Read x[n-numTaps-1] sample */
    00116       x0 = *(px++);
    00117
    00118       /* Perform the multiply-accumulate */
    00119       sum0 += (q63_t) x0 *c0;
    00120
    00121       /* Read the b[numTaps-2] coefficient */
    00122       c0 = *(pb++);
    00123
    00124       /* Read x[n-numTaps-2] sample */
    00125       x0 = *(px++);
    00126
    00127       /* Perform the multiply-accumulate */
    00128       sum0 += (q63_t) x0 *c0;
    00129
    00130       /* Read the b[numTaps-3] coefficient */
    00131       c0 = *(pb++);
    00132
    00133       /* Read x[n-numTaps-3] sample */
    00134       x0 = *(px++);
    00135
    00136       /* Perform the multiply-accumulate */
    00137       sum0 += (q63_t) x0 *c0;
    00138
    00139       /* Read the b[numTaps-4] coefficient */
    00140       c0 = *(pb++);
    00141
    00142       /* Read x[n-numTaps-4] sample */
    00143       x0 = *(px++);
    00144
    00145       /* Perform the multiply-accumulate */
    00146       sum0 += (q63_t) x0 *c0;
    00147
    00148       /* Decrement the loop counter */
    00149       tapCnt--;
    00150     }
    00151
    00152     /* If the filter length is not a multiple of 4, compute the remaining filter taps */
    00153     tapCnt = numTaps % 0x4u;
    00154
    00155     while(tapCnt > 0u)
    00156     {
    00157       /* Read coefficients */
    00158       c0 = *(pb++);
    00159
    00160       /* Fetch 1 state variable */
    00161       x0 = *(px++);
    00162
    00163       /* Perform the multiply-accumulate */
    00164       sum0 += (q63_t) x0 *c0;
    00165
    00166       /* Decrement the loop counter */
    00167       tapCnt--;
    00168     }
    00169
    00170     /* Advance the state pointer by the decimation factor
    00171      * to process the next group of decimation factor number samples */
    00172     pState = pState + S->M;
    00173
    00174     /* The result is in the accumulator, store in the destination buffer. */
    00175     *pDst++ = (q31_t) (sum0 >> 31);
    00176
    00177     /* Decrement the loop counter */
    00178     blkCnt--;
    00179   }
    00180
    00181   /* Processing is complete.
    00182    ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
    00183    ** This prepares the state buffer for the next function call. */
    00184
    00185   /* Points to the start of the state buffer */
    00186   pStateCurnt = S->pState;
    00187
    00188   i = (numTaps - 1u) >> 2u;
    00189
    00190   /* copy data */
    00191   while(i > 0u)
    00192   {
    00193     *pStateCurnt++ = *pState++;
    00194     *pStateCurnt++ = *pState++;
    00195     *pStateCurnt++ = *pState++;
    00196     *pStateCurnt++ = *pState++;
    00197
    00198     /* Decrement the loop counter */
    00199     i--;
    00200   }
    00201
    00202   i = (numTaps - 1u) % 0x04u;
    00203
    00204   /* copy data */
    00205   while(i > 0u)
    00206   {
    00207     *pStateCurnt++ = *pState++;
    00208
    00209     /* Decrement the loop counter */
    00210     i--;
    00211   }
    00212 }
    00213

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