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# arm_fir_q7.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_q7.c
    00009 *
    00010 * Description:  Q7 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
    00064 void arm_fir_q7(
    00065   const arm_fir_instance_q7 * S,
    00066   q7_t * pSrc,
    00067   q7_t * pDst,
    00068   uint32_t blockSize)
    00069 {
    00070
    00071 #ifndef ARM_MATH_CM0
    00072
    00073   /* Run the below code for Cortex-M4 and Cortex-M3 */
    00074
    00075   q7_t *pState = S->pState;                      /* State pointer */
    00076   q7_t *pCoeffs = S->pCoeffs;                    /* Coefficient pointer */
    00077   q7_t *pStateCurnt;                             /* Points to the current sample of the state */
    00078   q7_t x0, x1, x2, x3;                           /* Temporary variables to hold state */
    00079   q7_t c0;                                       /* Temporary variable to hold coefficient value */
    00080   q7_t *px;                                      /* Temporary pointer for state */
    00081   q7_t *pb;                                      /* Temporary pointer for coefficient buffer */
    00082   q31_t acc0, acc1, acc2, acc3;                  /* Accumulators */
    00083   uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
    00084   uint32_t i, tapCnt, blkCnt;                    /* Loop counters */
    00085
    00086   /* S->pState points to state array which contains previous frame (numTaps - 1) samples */
    00087   /* pStateCurnt points to the location where the new input data should be written */
    00088   pStateCurnt = &(S->pState[(numTaps - 1u)]);
    00089
    00090   /* Apply loop unrolling and compute 4 output values simultaneously.
    00091    * The variables acc0 ... acc3 hold output values that are being computed:
    00092    *
    00093    *    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]
    00094    *    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]
    00095    *    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]
    00096    *    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]
    00097    */
    00098   blkCnt = blockSize >> 2;
    00099
    00100   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00101    ** a second loop below computes the remaining 1 to 3 samples. */
    00102   while(blkCnt > 0u)
    00103   {
    00104     /* Copy four new input samples into the state buffer */
    00105     *pStateCurnt++ = *pSrc++;
    00106     *pStateCurnt++ = *pSrc++;
    00107     *pStateCurnt++ = *pSrc++;
    00108     *pStateCurnt++ = *pSrc++;
    00109
    00110     /* Set all accumulators to zero */
    00111     acc0 = 0;
    00112     acc1 = 0;
    00113     acc2 = 0;
    00114     acc3 = 0;
    00115
    00116     /* Initialize state pointer */
    00117     px = pState;
    00118
    00119     /* Initialize coefficient pointer */
    00120     pb = pCoeffs;
    00121
    00122     /* Read the first three samples from the state buffer:
    00123      *  x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */
    00124     x0 = *(px++);
    00125     x1 = *(px++);
    00126     x2 = *(px++);
    00127
    00128     /* Loop unrolling.  Process 4 taps at a time. */
    00129     tapCnt = numTaps >> 2;
    00130     i = tapCnt;
    00131
    00132     while(i > 0u)
    00133     {
    00134       /* Read the b[numTaps] coefficient */
    00135       c0 = *(pb++);
    00136
    00137       /* Read x[n-numTaps-3] sample */
    00138       x3 = *(px++);
    00139
    00140       /* acc0 +=  b[numTaps] * x[n-numTaps] */
    00141       acc0 += ((q15_t) x0 * c0);
    00142
    00143       /* acc1 +=  b[numTaps] * x[n-numTaps-1] */
    00144       acc1 += ((q15_t) x1 * c0);
    00145
    00146       /* acc2 +=  b[numTaps] * x[n-numTaps-2] */
    00147       acc2 += ((q15_t) x2 * c0);
    00148
    00149       /* acc3 +=  b[numTaps] * x[n-numTaps-3] */
    00150       acc3 += ((q15_t) x3 * c0);
    00151
    00152       /* Read the b[numTaps-1] coefficient */
    00153       c0 = *(pb++);
    00154
    00155       /* Read x[n-numTaps-4] sample */
    00156       x0 = *(px++);
    00157
    00158       /* Perform the multiply-accumulates */
    00159       acc0 += ((q15_t) x1 * c0);
    00160       acc1 += ((q15_t) x2 * c0);
    00161       acc2 += ((q15_t) x3 * c0);
    00162       acc3 += ((q15_t) x0 * c0);
    00163
    00164       /* Read the b[numTaps-2] coefficient */
    00165       c0 = *(pb++);
    00166
    00167       /* Read x[n-numTaps-5] sample */
    00168       x1 = *(px++);
    00169
    00170       /* Perform the multiply-accumulates */
    00171       acc0 += ((q15_t) x2 * c0);
    00172       acc1 += ((q15_t) x3 * c0);
    00173       acc2 += ((q15_t) x0 * c0);
    00174       acc3 += ((q15_t) x1 * c0);
    00175       /* Read the b[numTaps-3] coefficients */
    00176       c0 = *(pb++);
    00177
    00178       /* Read x[n-numTaps-6] sample */
    00179       x2 = *(px++);
    00180
    00181       /* Perform the multiply-accumulates */
    00182       acc0 += ((q15_t) x3 * c0);
    00183       acc1 += ((q15_t) x0 * c0);
    00184       acc2 += ((q15_t) x1 * c0);
    00185       acc3 += ((q15_t) x2 * c0);
    00186       i--;
    00187     }
    00188
    00189     /* If the filter length is not a multiple of 4, compute the remaining filter taps */
    00190
    00191     i = numTaps - (tapCnt * 4u);
    00192     while(i > 0u)
    00193     {
    00194       /* Read coefficients */
    00195       c0 = *(pb++);
    00196
    00197       /* Fetch 1 state variable */
    00198       x3 = *(px++);
    00199
    00200       /* Perform the multiply-accumulates */
    00201       acc0 += ((q15_t) x0 * c0);
    00202       acc1 += ((q15_t) x1 * c0);
    00203       acc2 += ((q15_t) x2 * c0);
    00204       acc3 += ((q15_t) x3 * c0);
    00205
    00206       /* Reuse the present sample states for next sample */
    00207       x0 = x1;
    00208       x1 = x2;
    00209       x2 = x3;
    00210
    00211       /* Decrement the loop counter */
    00212       i--;
    00213     }
    00214
    00215     /* Advance the state pointer by 4 to process the next group of 4 samples */
    00216     pState = pState + 4;
    00217
    00218     /* The results in the 4 accumulators are in 2.62 format.  Convert to 1.31
    00219      ** Then store the 4 outputs in the destination buffer. */
    00220     acc0 = __SSAT((acc0 >> 7u), 8);
    00221     *pDst++ = acc0;
    00222     acc1 = __SSAT((acc1 >> 7u), 8);
    00223     *pDst++ = acc1;
    00224     acc2 = __SSAT((acc2 >> 7u), 8);
    00225     *pDst++ = acc2;
    00226     acc3 = __SSAT((acc3 >> 7u), 8);
    00227     *pDst++ = acc3;
    00228
    00229     /* Decrement the samples loop counter */
    00230     blkCnt--;
    00231   }
    00232
    00233
    00234   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00235    ** No loop unrolling is used. */
    00236   blkCnt = blockSize % 4u;
    00237
    00238   while(blkCnt > 0u)
    00239   {
    00240     /* Copy one sample at a time into state buffer */
    00241     *pStateCurnt++ = *pSrc++;
    00242
    00243     /* Set the accumulator to zero */
    00244     acc0 = 0;
    00245
    00246     /* Initialize state pointer */
    00247     px = pState;
    00248
    00249     /* Initialize Coefficient pointer */
    00250     pb = (pCoeffs);
    00251
    00252     i = numTaps;
    00253
    00254     /* Perform the multiply-accumulates */
    00255     do
    00256     {
    00257       acc0 += (q15_t) * (px++) * (*(pb++));
    00258       i--;
    00259     } while(i > 0u);
    00260
    00261     /* The result is in 2.14 format.  Convert to 1.7
    00262      ** Then store the output in the destination buffer. */
    00263     *pDst++ = __SSAT((acc0 >> 7u), 8);
    00264
    00265     /* Advance state pointer by 1 for the next sample */
    00266     pState = pState + 1;
    00267
    00268     /* Decrement the samples loop counter */
    00269     blkCnt--;
    00270   }
    00271
    00272   /* Processing is complete.
    00273    ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
    00274    ** This prepares the state buffer for the next function call. */
    00275
    00276   /* Points to the start of the state buffer */
    00277   pStateCurnt = S->pState;
    00278
    00279   tapCnt = (numTaps - 1u) >> 2u;
    00280
    00281   /* copy data */
    00282   while(tapCnt > 0u)
    00283   {
    00284     *pStateCurnt++ = *pState++;
    00285     *pStateCurnt++ = *pState++;
    00286     *pStateCurnt++ = *pState++;
    00287     *pStateCurnt++ = *pState++;
    00288
    00289     /* Decrement the loop counter */
    00290     tapCnt--;
    00291   }
    00292
    00293   /* Calculate remaining number of copies */
    00294   tapCnt = (numTaps - 1u) % 0x4u;
    00295
    00296   /* Copy the remaining q31_t data */
    00297   while(tapCnt > 0u)
    00298   {
    00299     *pStateCurnt++ = *pState++;
    00300
    00301     /* Decrement the loop counter */
    00302     tapCnt--;
    00303   }
    00304
    00305 #else
    00306
    00307 /* Run the below code for Cortex-M0 */
    00308
    00309   uint32_t numTaps = S->numTaps;                 /* Number of taps in the filter */
    00310   uint32_t i, blkCnt;                            /* Loop counters */
    00311   q7_t *pState = S->pState;                      /* State pointer */
    00312   q7_t *pCoeffs = S->pCoeffs;                    /* Coefficient pointer */
    00313   q7_t *px, *pb;                                 /* Temporary pointers to state and coeff */
    00314   q31_t acc = 0;                                 /* Accumlator */
    00315   q7_t *pStateCurnt;                             /* Points to the current sample of the state */
    00316
    00317
    00318   /* S->pState points to state array which contains previous frame (numTaps - 1) samples */
    00319   /* pStateCurnt points to the location where the new input data should be written */
    00320   pStateCurnt = S->pState + (numTaps - 1u);
    00321
    00322   /* Initialize blkCnt with blockSize */
    00323   blkCnt = blockSize;
    00324
    00325   /* Perform filtering upto BlockSize - BlockSize%4  */
    00326   while(blkCnt > 0u)
    00327   {
    00328     /* Copy one sample at a time into state buffer */
    00329     *pStateCurnt++ = *pSrc++;
    00330
    00331     /* Set accumulator to zero */
    00332     acc = 0;
    00333
    00334     /* Initialize state pointer of type q7 */
    00335     px = pState;
    00336
    00337     /* Initialize coeff pointer of type q7 */
    00338     pb = pCoeffs;
    00339
    00340
    00341     i = numTaps;
    00342
    00343     while(i > 0u)
    00344     {
    00345       /* 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] */
    00346       acc += (q15_t) * px++ * *pb++;
    00347       i--;
    00348     }
    00349
    00350     /* Store the 1.7 format filter output in destination buffer */
    00351     *pDst++ = (q7_t) __SSAT((acc >> 7), 8);
    00352
    00353     /* Advance the state pointer by 1 to process the next sample */
    00354     pState = pState + 1;
    00355
    00356     /* Decrement the loop counter */
    00357     blkCnt--;
    00358   }
    00359
    00360   /* Processing is complete.
    00361    ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
    00362    ** This prepares the state buffer for the next function call. */
    00363
    00364
    00365   /* Points to the start of the state buffer */
    00366   pStateCurnt = S->pState;
    00367
    00368
    00369   /* Copy numTaps number of values */
    00370   i = (numTaps - 1u);
    00371
    00372   /* Copy q7_t data */
    00373   while(i > 0u)
    00374   {
    00375     *pStateCurnt++ = *pState++;
    00376     i--;
    00377   }
    00378
    00379 #endif /*   #ifndef ARM_MATH_CM0 */
    00380
    00381 }
    00382

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