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# arm_iir_lattice_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_iir_lattice_q31.c
    00009 *
    00010 * Description:  Q31 IIR lattice 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 0.0.7  2010/06/10
    00027 *    Misra-C changes done
    00028 * -------------------------------------------------------------------- */
    00029
    00030 #include "arm_math.h"
    00031
    00059 void arm_iir_lattice_q31(
    00060   const arm_iir_lattice_instance_q31 * S,
    00061   q31_t * pSrc,
    00062   q31_t * pDst,
    00063   uint32_t blockSize)
    00064 {
    00065   q31_t fcurr, fnext, gcurr = 0, gnext;          /* Temporary variables for lattice stages */
    00066   q63_t acc;                                     /* Accumlator */
    00067   uint32_t blkCnt, tapCnt;                       /* Temporary variables for counts */
    00068   q31_t *px1, *px2, *pk, *pv;                    /* Temporary pointers for state and coef */
    00069   uint32_t numStages = S->numStages;             /* number of stages */
    00070   q31_t *pState;                                 /* State pointer */
    00071   q31_t *pStateCurnt;                            /* State current pointer */
    00072
    00073   blkCnt = blockSize;
    00074
    00075   pState = &S->pState[0];
    00076
    00077   /* Sample processing */
    00078   while(blkCnt > 0u)
    00079   {
    00080     /* Read Sample from input buffer */
    00081     /* fN(n) = x(n) */
    00082     fcurr = *pSrc++;
    00083
    00084     /* Initialize state read pointer */
    00085     px1 = pState;
    00086     /* Initialize state write pointer */
    00087     px2 = pState;
    00088     /* Set accumulator to zero */
    00089     acc = 0;
    00090     /* Initialize Ladder coeff pointer */
    00091     pv = &S->pvCoeffs[0];
    00092     /* Initialize Reflection coeff pointer */
    00093     pk = &S->pkCoeffs[0];
    00094
    00095
    00096     /* Process sample for first tap */
    00097     gcurr = *px1++;
    00098     /* fN-1(n) = fN(n) - kN * gN-1(n-1) */
    00099     fnext = __QSUB(fcurr, (q31_t) (((q63_t) gcurr * (*pk)) >> 31));
    00100     /* gN(n) = kN * fN-1(n) + gN-1(n-1) */
    00101     gnext = __QADD(gcurr, (q31_t) (((q63_t) fnext * (*pk++)) >> 31));
    00102     /* write gN-1(n-1) into state for next sample processing */
    00103     *px2++ = gnext;
    00104     /* y(n) += gN(n) * vN  */
    00105     acc += ((q63_t) gnext * *pv++);
    00106
    00107     /* Update f values for next coefficient processing */
    00108     fcurr = fnext;
    00109
    00110     /* Loop unrolling.  Process 4 taps at a time. */
    00111     tapCnt = (numStages - 1u) >> 2;
    00112
    00113     while(tapCnt > 0u)
    00114     {
    00115
    00116       /* Process sample for 2nd, 6th .. taps */
    00117       /* Read gN-2(n-1) from state buffer */
    00118       gcurr = *px1++;
    00119       /* fN-2(n) = fN-1(n) - kN-1 * gN-2(n-1) */
    00120       fnext = __QSUB(fcurr, (q31_t) (((q63_t) gcurr * (*pk)) >> 31));
    00121       /* gN-1(n) = kN-1 * fN-2(n) + gN-2(n-1) */
    00122       gnext = __QADD(gcurr, (q31_t) (((q63_t) fnext * (*pk++)) >> 31));
    00123       /* y(n) += gN-1(n) * vN-1  */
    00124       /* process for gN-5(n) * vN-5, gN-9(n) * vN-9 ... */
    00125       acc += ((q63_t) gnext * *pv++);
    00126       /* write gN-1(n) into state for next sample processing */
    00127       *px2++ = gnext;
    00128
    00129       /* Process sample for 3nd, 7th ...taps */
    00130       /* Read gN-3(n-1) from state buffer */
    00131       gcurr = *px1++;
    00132       /* Process sample for 3rd, 7th .. taps */
    00133       /* fN-3(n) = fN-2(n) - kN-2 * gN-3(n-1) */
    00134       fcurr = __QSUB(fnext, (q31_t) (((q63_t) gcurr * (*pk)) >> 31));
    00135       /* gN-2(n) = kN-2 * fN-3(n) + gN-3(n-1) */
    00136       gnext = __QADD(gcurr, (q31_t) (((q63_t) fcurr * (*pk++)) >> 31));
    00137       /* y(n) += gN-2(n) * vN-2  */
    00138       /* process for gN-6(n) * vN-6, gN-10(n) * vN-10 ... */
    00139       acc += ((q63_t) gnext * *pv++);
    00140       /* write gN-2(n) into state for next sample processing */
    00141       *px2++ = gnext;
    00142
    00143
    00144       /* Process sample for 4th, 8th ...taps */
    00145       /* Read gN-4(n-1) from state buffer */
    00146       gcurr = *px1++;
    00147       /* Process sample for 4th, 8th .. taps */
    00148       /* fN-4(n) = fN-3(n) - kN-3 * gN-4(n-1) */
    00149       fnext = __QSUB(fcurr, (q31_t) (((q63_t) gcurr * (*pk)) >> 31));
    00150       /* gN-3(n) = kN-3 * fN-4(n) + gN-4(n-1) */
    00151       gnext = __QADD(gcurr, (q31_t) (((q63_t) fnext * (*pk++)) >> 31));
    00152       /* y(n) += gN-3(n) * vN-3  */
    00153       /* process for gN-7(n) * vN-7, gN-11(n) * vN-11 ... */
    00154       acc += ((q63_t) gnext * *pv++);
    00155       /* write gN-3(n) into state for next sample processing */
    00156       *px2++ = gnext;
    00157
    00158
    00159       /* Process sample for 5th, 9th ...taps */
    00160       /* Read gN-5(n-1) from state buffer */
    00161       gcurr = *px1++;
    00162       /* Process sample for 5th, 9th .. taps */
    00163       /* fN-5(n) = fN-4(n) - kN-4 * gN-1(n-1) */
    00164       fcurr = __QSUB(fnext, (q31_t) (((q63_t) gcurr * (*pk)) >> 31));
    00165       /* gN-4(n) = kN-4 * fN-5(n) + gN-5(n-1) */
    00166       gnext = __QADD(gcurr, (q31_t) (((q63_t) fcurr * (*pk++)) >> 31));
    00167       /* y(n) += gN-4(n) * vN-4  */
    00168       /* process for gN-8(n) * vN-8, gN-12(n) * vN-12 ... */
    00169       acc += ((q63_t) gnext * *pv++);
    00170       /* write gN-4(n) into state for next sample processing */
    00171       *px2++ = gnext;
    00172
    00173       tapCnt--;
    00174
    00175     }
    00176
    00177     fnext = fcurr;
    00178
    00179     /* If the filter length is not a multiple of 4, compute the remaining filter taps */
    00180     tapCnt = (numStages - 1u) % 0x4u;
    00181
    00182     while(tapCnt > 0u)
    00183     {
    00184       gcurr = *px1++;
    00185       /* Process sample for last taps */
    00186       fnext = __QSUB(fcurr, (q31_t) (((q63_t) gcurr * (*pk)) >> 31));
    00187       gnext = __QADD(gcurr, (q31_t) (((q63_t) fnext * (*pk++)) >> 31));
    00188       /* Output samples for last taps */
    00189       acc += ((q63_t) gnext * *pv++);
    00190       *px2++ = gnext;
    00191       fcurr = fnext;
    00192
    00193       tapCnt--;
    00194
    00195     }
    00196
    00197     /* y(n) += g0(n) * v0 */
    00198     acc += (q63_t) fnext *(
    00199   *pv++);
    00200
    00201     *px2++ = fnext;
    00202
    00203     /* write out into pDst */
    00204     *pDst++ = (q31_t) (acc >> 31u);
    00205
    00206     /* Advance the state pointer by 4 to process the next group of 4 samples */
    00207     pState = pState + 1u;
    00208     blkCnt--;
    00209
    00210   }
    00211
    00212   /* Processing is complete. Now copy last S->numStages samples to start of the buffer
    00213      for the preperation of next frame process */
    00214
    00215   /* Points to the start of the state buffer */
    00216   pStateCurnt = &S->pState[0];
    00217   pState = &S->pState[blockSize];
    00218
    00219   tapCnt = numStages >> 2u;
    00220
    00221   /* copy data */
    00222   while(tapCnt > 0u)
    00223   {
    00224     *pStateCurnt++ = *pState++;
    00225     *pStateCurnt++ = *pState++;
    00226     *pStateCurnt++ = *pState++;
    00227     *pStateCurnt++ = *pState++;
    00228
    00229     /* Decrement the loop counter */
    00230     tapCnt--;
    00231
    00232   }
    00233
    00234   /* Calculate remaining number of copies */
    00235   tapCnt = (numStages) % 0x4u;
    00236
    00237   /* Copy the remaining q31_t data */
    00238   while(tapCnt > 0u)
    00239   {
    00240     *pStateCurnt++ = *pState++;
    00241
    00242     /* Decrement the loop counter */
    00243     tapCnt--;
    00244   };
    00245
    00246 }
    00247
    00248
    00249
    00250

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