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# arm_fir_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_fir_lattice_q31.c
    00009 *
    00010 * Description:  Q31 FIR 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
    00055 void arm_fir_lattice_q31(
    00056   const arm_fir_lattice_instance_q31 * S,
    00057   q31_t * pSrc,
    00058   q31_t * pDst,
    00059   uint32_t blockSize)
    00060 {
    00061   q31_t *pState;                                 /* State pointer */
    00062   q31_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
    00063   q31_t *px;                                     /* temporary state pointer */
    00064   q31_t *pk;                                     /* temporary coefficient pointer */
    00065   q31_t fcurr1, fnext1, gcurr1 = 0, gnext1;      /* temporary variables for first sample in loop unrolling */
    00066   q63_t fcurr2, fnext2, gnext2;                  /* temporary variables for second sample in loop unrolling */
    00067   q63_t fcurr3, fnext3, gnext3;                  /* temporary variables for third sample in loop unrolling */
    00068   q63_t fcurr4, fnext4, gnext4;                  /* temporary variables for fourth sample in loop unrolling */
    00069   uint32_t numStages = S->numStages;             /* Length of the filter */
    00070   uint32_t blkCnt, stageCnt;                     /* temporary variables for counts */
    00071
    00072   pState = &S->pState[0];
    00073
    00074   blkCnt = blockSize >> 2u;
    00075
    00076   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00077    ** a second loop below computes the remaining 1 to 3 samples. */
    00078   while(blkCnt > 0u)
    00079   {
    00080
    00081     /* Read two samples from input buffer */
    00082     /* f0(n) = x(n) */
    00083     fcurr1 = *pSrc++;
    00084     /* f0(n) = x(n) */
    00085     fcurr2 = *pSrc++;
    00086
    00087     /* Initialize coeff pointer */
    00088     pk = (pCoeffs);
    00089
    00090     /* Initialize state pointer */
    00091     px = pState;
    00092
    00093     /* Read g0(n-1) from state */
    00094     gcurr1 = *px;
    00095
    00096     /* Process first sample for first tap */
    00097     /* f1(n) = f0(n) +  K1 * g0(n-1) */
    00098     fnext1 = (q31_t) (((q63_t) gcurr1 * (*pk)) >> 31) + fcurr1;
    00099     /* g1(n) = f0(n) * K1  +  g0(n-1) */
    00100     gnext1 = (q31_t) (((q63_t) fcurr1 * (*pk)) >> 31) + gcurr1;
    00101
    00102     /* Process second sample for first tap */
    00103     /* for sample 2 processing */
    00104     fnext2 = (q31_t) (((q63_t) fcurr1 * (*pk)) >> 31) + fcurr2;
    00105     gnext2 = (q31_t) (((q63_t) fcurr2 * (*pk)) >> 31) + fcurr1;
    00106
    00107
    00108     /* Read next two samples from input buffer */
    00109     /* f0(n+2) = x(n+2) */
    00110     fcurr3 = *pSrc++;
    00111     fcurr4 = *pSrc++;
    00112
    00113     /* Copy only last input samples into the state buffer
    00114        which will be used for next four samples processing */
    00115     *px++ = (q31_t) fcurr4;
    00116
    00117     /* Process third sample for first tap */
    00118     fnext3 = (q31_t) (((q63_t) fcurr2 * (*pk)) >> 31) + fcurr3;
    00119     gnext3 = (q31_t) (((q63_t) fcurr3 * (*pk)) >> 31) + fcurr2;
    00120
    00121     /* Process fourth sample for first tap */
    00122     fnext4 = (q31_t) (((q63_t) fcurr3 * (*pk)) >> 31) + fcurr4;
    00123     gnext4 = (q31_t) (((q63_t) fcurr4 * (*pk++)) >> 31) + fcurr3;
    00124
    00125     /* save g1(n) in state buffer for next sample processing */
    00126     /* *px++ = gnext4;       */
    00127
    00128     /* Update of f values for next coefficient set processing */
    00129     fcurr1 = fnext1;
    00130     fcurr2 = fnext2;
    00131     fcurr3 = fnext3;
    00132     fcurr4 = fnext4;
    00133
    00134
    00135     /* Loop unrolling.  Process 4 taps at a time . */
    00136     stageCnt = (numStages - 1u) >> 2u;
    00137
    00138
    00139     /* Loop over the number of taps.  Unroll by a factor of 4.
    00140      ** Repeat until we've computed numStages-3 coefficients. */
    00141
    00142     /* Process 2nd, 3rd, 4th and 5th taps ... here */
    00143     while(stageCnt > 0u)
    00144     {
    00145       /* Read g1(n-1), g3(n-1) .... from state */
    00146       gcurr1 = *px;
    00147
    00148       /* save g1(n) in state buffer */
    00149       *px++ = (q31_t) gnext4;
    00150
    00151       /* Process first sample for 2nd, 6th .. tap */
    00152       /* Sample processing for K2, K6.... */
    00153       /* f2(n) = f1(n) +  K2 * g1(n-1) */
    00154       fnext1 = (q31_t) (((q63_t) gcurr1 * (*pk)) >> 31) + fcurr1;
    00155       /* Process second sample for 2nd, 6th .. tap */
    00156       /* for sample 2 processing */
    00157       fnext2 = (q31_t) (((q63_t) gnext1 * (*pk)) >> 31) + fcurr2;
    00158       /* Process third sample for 2nd, 6th .. tap */
    00159       fnext3 = (q31_t) (((q63_t) gnext2 * (*pk)) >> 31) + fcurr3;
    00160       /* Process fourth sample for 2nd, 6th .. tap */
    00161       fnext4 = (q31_t) (((q63_t) gnext3 * (*pk)) >> 31) + fcurr4;
    00162
    00163       /* g2(n) = f1(n) * K2  +  g1(n-1) */
    00164       /* Calculation of state values for next stage */
    00165       gnext4 = (q31_t) (((q63_t) fcurr4 * (*pk)) >> 31) + gnext3;
    00166       gnext3 = (q31_t) (((q63_t) fcurr3 * (*pk)) >> 31) + gnext2;
    00167       gnext2 = (q31_t) (((q63_t) fcurr2 * (*pk)) >> 31) + gnext1;
    00168       gnext1 = (q31_t) (((q63_t) fcurr1 * (*pk++)) >> 31) + gcurr1;
    00169
    00170
    00171       /* Read g2(n-1), g4(n-1) .... from state */
    00172       gcurr1 = *px;
    00173
    00174       /* save g2(n) in state buffer */
    00175       *px++ = (q31_t) gnext4;
    00176
    00177       /* Sample processing for K3, K7.... */
    00178       /* Process first sample for 3rd, 7th .. tap */
    00179       /* f3(n) = f2(n) +  K3 * g2(n-1) */
    00180       fcurr1 = (q31_t) (((q63_t) gcurr1 * (*pk)) >> 31) + fnext1;
    00181       /* Process second sample for 3rd, 7th .. tap */
    00182       fcurr2 = (q31_t) (((q63_t) gnext1 * (*pk)) >> 31) + fnext2;
    00183       /* Process third sample for 3rd, 7th .. tap */
    00184       fcurr3 = (q31_t) (((q63_t) gnext2 * (*pk)) >> 31) + fnext3;
    00185       /* Process fourth sample for 3rd, 7th .. tap */
    00186       fcurr4 = (q31_t) (((q63_t) gnext3 * (*pk)) >> 31) + fnext4;
    00187
    00188       /* Calculation of state values for next stage */
    00189       /*  gnext4 = fnext4 * (*pk) +  gnext3; */
    00190       gnext4 = (q31_t) (((q63_t) fnext4 * (*pk)) >> 31) + gnext3;
    00191       gnext3 = (q31_t) (((q63_t) fnext3 * (*pk)) >> 31) + gnext2;
    00192       /*  gnext2 = fnext2 * (*pk) +  gnext1; */
    00193       gnext2 = (q31_t) (((q63_t) fnext2 * (*pk)) >> 31) + gnext1;
    00194
    00195       /* g1(n) = f0(n) * K1  +  g0(n-1) */
    00196       /*  gnext1 = fnext1 * (*pk++) +  gcurr1; */
    00197       gnext1 = (q31_t) (((q63_t) fnext1 * (*pk++)) >> 31) + gcurr1;
    00198
    00199       /* Read g1(n-1), g3(n-1) .... from state */
    00200       gcurr1 = *px;
    00201
    00202       /* save g1(n) in state buffer */
    00203       *px++ = (q31_t) gnext4;
    00204
    00205       /* Sample processing for K4, K8.... */
    00206       /* Process first sample for 4th, 8th .. tap */
    00207       /* f4(n) = f3(n) +  K4 * g3(n-1) */
    00208       fnext1 = (q31_t) (((q63_t) gcurr1 * (*pk)) >> 31) + fcurr1;
    00209       /* Process second sample for 4th, 8th .. tap */
    00210       /* for sample 2 processing */
    00211       fnext2 = (q31_t) (((q63_t) gnext1 * (*pk)) >> 31) + fcurr2;
    00212       /* Process third sample for 4th, 8th .. tap */
    00213       fnext3 = (q31_t) (((q63_t) gnext2 * (*pk)) >> 31) + fcurr3;
    00214       /* Process fourth sample for 4th, 8th .. tap */
    00215       fnext4 = (q31_t) (((q63_t) gnext3 * (*pk)) >> 31) + fcurr4;
    00216
    00217       /* g4(n) = f3(n) * K4  +  g3(n-1) */
    00218       /* Calculation of state values for next stage */
    00219       gnext4 = (q31_t) (((q63_t) fcurr4 * (*pk)) >> 31) + gnext3;
    00220       gnext3 = (q31_t) (((q63_t) fcurr3 * (*pk)) >> 31) + gnext2;
    00221       gnext2 = (q31_t) (((q63_t) fcurr2 * (*pk)) >> 31) + gnext1;
    00222       gnext1 = (q31_t) (((q63_t) fcurr1 * (*pk++)) >> 31) + gcurr1;
    00223
    00224       /* Read g2(n-1), g4(n-1) .... from state */
    00225       gcurr1 = *px;
    00226
    00227       /* save g4(n) in state buffer */
    00228       *px++ = (q31_t) gnext4;
    00229
    00230       /* Sample processing for K5, K9.... */
    00231       /* Process first sample for 5th, 9th .. tap */
    00232       /* f5(n) = f4(n) +  K5 * g4(n-1) */
    00233       fcurr1 = (q31_t) (((q63_t) gcurr1 * (*pk)) >> 31) + fnext1;
    00234       /* Process second sample for 5th, 9th .. tap */
    00235       fcurr2 = (q31_t) (((q63_t) gnext1 * (*pk)) >> 31) + fnext2;
    00236       /* Process third sample for 5th, 9th .. tap */
    00237       fcurr3 = (q31_t) (((q63_t) gnext2 * (*pk)) >> 31) + fnext3;
    00238       /* Process fourth sample for 5th, 9th .. tap */
    00239       fcurr4 = (q31_t) (((q63_t) gnext3 * (*pk)) >> 31) + fnext4;
    00240
    00241       /* Calculation of state values for next stage */
    00242       /* g5(n) = f4(n) * K5  +  g4(n-1) */
    00243       gnext4 = (q31_t) (((q63_t) fnext4 * (*pk)) >> 31) + gnext3;
    00244       gnext3 = (q31_t) (((q63_t) fnext3 * (*pk)) >> 31) + gnext2;
    00245       gnext2 = (q31_t) (((q63_t) fnext2 * (*pk)) >> 31) + gnext1;
    00246       gnext1 = (q31_t) (((q63_t) fnext1 * (*pk++)) >> 31) + gcurr1;
    00247
    00248       stageCnt--;
    00249     }
    00250
    00251     /* If the (filter length -1) is not a multiple of 4, compute the remaining filter taps */
    00252     stageCnt = (numStages - 1u) % 0x4u;
    00253
    00254     while(stageCnt > 0u)
    00255     {
    00256       gcurr1 = *px;
    00257
    00258       /* save g value in state buffer */
    00259       *px++ = (q31_t) gnext4;
    00260
    00261       /* Process four samples for last three taps here */
    00262       fnext1 = (q31_t) (((q63_t) gcurr1 * (*pk)) >> 31) + fcurr1;
    00263       fnext2 = (q31_t) (((q63_t) gnext1 * (*pk)) >> 31) + fcurr2;
    00264       fnext3 = (q31_t) (((q63_t) gnext2 * (*pk)) >> 31) + fcurr3;
    00265       fnext4 = (q31_t) (((q63_t) gnext3 * (*pk)) >> 31) + fcurr4;
    00266
    00267       /* g1(n) = f0(n) * K1  +  g0(n-1) */
    00268       gnext4 = (q31_t) (((q63_t) fcurr4 * (*pk)) >> 31) + gnext3;
    00269       gnext3 = (q31_t) (((q63_t) fcurr3 * (*pk)) >> 31) + gnext2;
    00270       gnext2 = (q31_t) (((q63_t) fcurr2 * (*pk)) >> 31) + gnext1;
    00271       gnext1 = (q31_t) (((q63_t) fcurr1 * (*pk++)) >> 31) + gcurr1;
    00272
    00273       /* Update of f values for next coefficient set processing */
    00274       fcurr1 = fnext1;
    00275       fcurr2 = fnext2;
    00276       fcurr3 = fnext3;
    00277       fcurr4 = fnext4;
    00278
    00279       stageCnt--;
    00280
    00281     }
    00282
    00283     /* The results in the 4 accumulators, store in the destination buffer. */
    00284     /* y(n) = fN(n) */
    00285     *pDst++ = fcurr1;
    00286     *pDst++ = (q31_t) fcurr2;
    00287     *pDst++ = (q31_t) fcurr3;
    00288     *pDst++ = (q31_t) fcurr4;
    00289
    00290     blkCnt--;
    00291   }
    00292
    00293   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00294    ** No loop unrolling is used. */
    00295   blkCnt = blockSize % 0x4u;
    00296
    00297   while(blkCnt > 0u)
    00298   {
    00299     /* f0(n) = x(n) */
    00300     fcurr1 = *pSrc++;
    00301
    00302     /* Initialize coeff pointer */
    00303     pk = (pCoeffs);
    00304
    00305     /* Initialize state pointer */
    00306     px = pState;
    00307
    00308     /* read g2(n) from state buffer */
    00309     gcurr1 = *px;
    00310
    00311     /* for sample 1 processing */
    00312     /* f1(n) = f0(n) +  K1 * g0(n-1) */
    00313     fnext1 = (q31_t) (((q63_t) gcurr1 * (*pk)) >> 31) + fcurr1;
    00314     /* g1(n) = f0(n) * K1  +  g0(n-1) */
    00315     gnext1 = (q31_t) (((q63_t) fcurr1 * (*pk++)) >> 31) + gcurr1;
    00316     /* save g1(n) in state buffer */
    00317     *px++ = fcurr1;
    00318
    00319     /* f1(n) is saved in fcurr1
    00320        for next stage processing */
    00321     fcurr1 = fnext1;
    00322
    00323     stageCnt = (numStages - 1u);
    00324
    00325     /* stage loop */
    00326     while(stageCnt > 0u)
    00327     {
    00328       /* read g2(n) from state buffer */
    00329       gcurr1 = *px;
    00330
    00331       /* save g1(n) in state buffer */
    00332       *px++ = gnext1;
    00333
    00334       /* Sample processing for K2, K3.... */
    00335       /* f2(n) = f1(n) +  K2 * g1(n-1) */
    00336       fnext1 = (q31_t) (((q63_t) gcurr1 * (*pk)) >> 31) + fcurr1;
    00337       /* g2(n) = f1(n) * K2  +  g1(n-1) */
    00338       gnext1 = (q31_t) (((q63_t) fcurr1 * (*pk++)) >> 31) + gcurr1;
    00339
    00340       /* f1(n) is saved in fcurr1
    00341          for next stage processing */
    00342       fcurr1 = fnext1;
    00343
    00344       stageCnt--;
    00345
    00346     }
    00347
    00348     /* y(n) = fN(n) */
    00349     *pDst++ = fcurr1;
    00350
    00351     blkCnt--;
    00352
    00353   }
    00354 }
    00355

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