tmk_core/tool/mbed/mbed-sdk/libraries/dsp/cmsis_dsp/FilteringFunctions/arm_fir_decimate_q31.c

   1 /* ----------------------------------------------------------------------
   2 * Copyright (C) 2010-2013 ARM Limited. All rights reserved.
   3 *
   4 * $Date:        17. January 2013
   5 * $Revision:    V1.4.1
   6 *
   7 * Project:          CMSIS DSP Library
   8 * Title:            arm_fir_decimate_q31.c
   9 *
  10 * Description:  Q31 FIR Decimator.
  11 *
  12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
  13 *
  14 * Redistribution and use in source and binary forms, with or without
  15 * modification, are permitted provided that the following conditions
  16 * are met:
  17 *   - Redistributions of source code must retain the above copyright
  18 *     notice, this list of conditions and the following disclaimer.
  19 *   - Redistributions in binary form must reproduce the above copyright
  20 *     notice, this list of conditions and the following disclaimer in
  21 *     the documentation and/or other materials provided with the
  22 *     distribution.
  23 *   - Neither the name of ARM LIMITED nor the names of its contributors
  24 *     may be used to endorse or promote products derived from this
  25 *     software without specific prior written permission.
  26 *
  27 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  28 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  29 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  30 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  31 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  32 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  33 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  34 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  35 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  37 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  38 * POSSIBILITY OF SUCH DAMAGE.
  39 * -------------------------------------------------------------------- */
  40
  41 #include "arm_math.h"
  42
  43 /**
  44  * @ingroup groupFilters
  45  */
  46
  47 /**
  48  * @addtogroup FIR_decimate
  49  * @{
  50  */
  51
  52 /**
  53  * @brief Processing function for the Q31 FIR decimator.
  54  * @param[in] *S points to an instance of the Q31 FIR decimator structure.
  55  * @param[in] *pSrc points to the block of input data.
  56  * @param[out] *pDst points to the block of output data
  57  * @param[in] blockSize number of input samples to process per call.
  58  * @return none
  59  *
  60  * <b>Scaling and Overflow Behavior:</b>
  61  * \par
  62  * The function is implemented using an internal 64-bit accumulator.
  63  * The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.
  64  * Thus, if the accumulator result overflows it wraps around rather than clip.
  65  * In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (where log2 is read as log to the base 2).
  66  * After all multiply-accumulates are performed, the 2.62 accumulator is truncated to 1.32 format and then saturated to 1.31 format.
  67  *
  68  * \par
  69  * Refer to the function <code>arm_fir_decimate_fast_q31()</code> for a faster but less precise implementation of this function for Cortex-M3 and Cortex-M4.
  70  */
  71
  72 void arm_fir_decimate_q31(
  73   const arm_fir_decimate_instance_q31 * S,
  74   q31_t * pSrc,
  75   q31_t * pDst,
  76   uint32_t blockSize)
  77 {
  78   q31_t *pState = S->pState;                     /* State pointer */
  79   q31_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
  80   q31_t *pStateCurnt;                            /* Points to the current sample of the state */
  81   q31_t x0, c0;                                  /* Temporary variables to hold state and coefficient values */
  82   q31_t *px;                                     /* Temporary pointers for state buffer */
  83   q31_t *pb;                                     /* Temporary pointers for coefficient buffer */
  84   q63_t sum0;                                    /* Accumulator */
  85   uint32_t numTaps = S->numTaps;                 /* Number of taps */
  86   uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M;  /* Loop counters */
  87
  88
  89 #ifndef ARM_MATH_CM0_FAMILY
  90
  91   /* Run the below code for Cortex-M4 and Cortex-M3 */
  92
  93   /* S->pState buffer contains previous frame (numTaps - 1) samples */
  94   /* pStateCurnt points to the location where the new input data should be written */
  95   pStateCurnt = S->pState + (numTaps - 1u);
  96
  97   /* Total number of output samples to be computed */
  98   blkCnt = outBlockSize;
  99
 100   while(blkCnt > 0u)
 101   {
 102     /* Copy decimation factor number of new input samples into the state buffer */
 103     i = S->M;
 104
 105     do
 106     {
 107       *pStateCurnt++ = *pSrc++;
 108
 109     } while(--i);
 110
 111     /* Set accumulator to zero */
 112     sum0 = 0;
 113
 114     /* Initialize state pointer */
 115     px = pState;
 116
 117     /* Initialize coeff pointer */
 118     pb = pCoeffs;
 119
 120     /* Loop unrolling.  Process 4 taps at a time. */
 121     tapCnt = numTaps >> 2;
 122
 123     /* Loop over the number of taps.  Unroll by a factor of 4.
 124      ** Repeat until we've computed numTaps-4 coefficients. */
 125     while(tapCnt > 0u)
 126     {
 127       /* Read the b[numTaps-1] coefficient */
 128       c0 = *(pb++);
 129
 130       /* Read x[n-numTaps-1] sample */
 131       x0 = *(px++);
 132
 133       /* Perform the multiply-accumulate */
 134       sum0 += (q63_t) x0 *c0;
 135
 136       /* Read the b[numTaps-2] coefficient */
 137       c0 = *(pb++);
 138
 139       /* Read x[n-numTaps-2] sample */
 140       x0 = *(px++);
 141
 142       /* Perform the multiply-accumulate */
 143       sum0 += (q63_t) x0 *c0;
 144
 145       /* Read the b[numTaps-3] coefficient */
 146       c0 = *(pb++);
 147
 148       /* Read x[n-numTaps-3] sample */
 149       x0 = *(px++);
 150
 151       /* Perform the multiply-accumulate */
 152       sum0 += (q63_t) x0 *c0;
 153
 154       /* Read the b[numTaps-4] coefficient */
 155       c0 = *(pb++);
 156
 157       /* Read x[n-numTaps-4] sample */
 158       x0 = *(px++);
 159
 160       /* Perform the multiply-accumulate */
 161       sum0 += (q63_t) x0 *c0;
 162
 163       /* Decrement the loop counter */
 164       tapCnt--;
 165     }
 166
 167     /* If the filter length is not a multiple of 4, compute the remaining filter taps */
 168     tapCnt = numTaps % 0x4u;
 169
 170     while(tapCnt > 0u)
 171     {
 172       /* Read coefficients */
 173       c0 = *(pb++);
 174
 175       /* Fetch 1 state variable */
 176       x0 = *(px++);
 177
 178       /* Perform the multiply-accumulate */
 179       sum0 += (q63_t) x0 *c0;
 180
 181       /* Decrement the loop counter */
 182       tapCnt--;
 183     }
 184
 185     /* Advance the state pointer by the decimation factor
 186      * to process the next group of decimation factor number samples */
 187     pState = pState + S->M;
 188
 189     /* The result is in the accumulator, store in the destination buffer. */
 190     *pDst++ = (q31_t) (sum0 >> 31);
 191
 192     /* Decrement the loop counter */
 193     blkCnt--;
 194   }
 195
 196   /* Processing is complete.
 197    ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
 198    ** This prepares the state buffer for the next function call. */
 199
 200   /* Points to the start of the state buffer */
 201   pStateCurnt = S->pState;
 202
 203   i = (numTaps - 1u) >> 2u;
 204
 205   /* copy data */
 206   while(i > 0u)
 207   {
 208     *pStateCurnt++ = *pState++;
 209     *pStateCurnt++ = *pState++;
 210     *pStateCurnt++ = *pState++;
 211     *pStateCurnt++ = *pState++;
 212
 213     /* Decrement the loop counter */
 214     i--;
 215   }
 216
 217   i = (numTaps - 1u) % 0x04u;
 218
 219   /* copy data */
 220   while(i > 0u)
 221   {
 222     *pStateCurnt++ = *pState++;
 223
 224     /* Decrement the loop counter */
 225     i--;
 226   }
 227
 228 #else
 229
 230 /* Run the below code for Cortex-M0 */
 231
 232   /* S->pState buffer contains previous frame (numTaps - 1) samples */
 233   /* pStateCurnt points to the location where the new input data should be written */
 234   pStateCurnt = S->pState + (numTaps - 1u);
 235
 236   /* Total number of output samples to be computed */
 237   blkCnt = outBlockSize;
 238
 239   while(blkCnt > 0u)
 240   {
 241     /* Copy decimation factor number of new input samples into the state buffer */
 242     i = S->M;
 243
 244     do
 245     {
 246       *pStateCurnt++ = *pSrc++;
 247
 248     } while(--i);
 249
 250     /* Set accumulator to zero */
 251     sum0 = 0;
 252
 253     /* Initialize state pointer */
 254     px = pState;
 255
 256     /* Initialize coeff pointer */
 257     pb = pCoeffs;
 258
 259     tapCnt = numTaps;
 260
 261     while(tapCnt > 0u)
 262     {
 263       /* Read coefficients */
 264       c0 = *pb++;
 265
 266       /* Fetch 1 state variable */
 267       x0 = *px++;
 268
 269       /* Perform the multiply-accumulate */
 270       sum0 += (q63_t) x0 *c0;
 271
 272       /* Decrement the loop counter */
 273       tapCnt--;
 274     }
 275
 276     /* Advance the state pointer by the decimation factor
 277      * to process the next group of decimation factor number samples */
 278     pState = pState + S->M;
 279
 280     /* The result is in the accumulator, store in the destination buffer. */
 281     *pDst++ = (q31_t) (sum0 >> 31);
 282
 283     /* Decrement the loop counter */
 284     blkCnt--;
 285   }
 286
 287   /* Processing is complete.
 288    ** Now copy the last numTaps - 1 samples to the start of the state buffer.
 289    ** This prepares the state buffer for the next function call. */
 290
 291   /* Points to the start of the state buffer */
 292   pStateCurnt = S->pState;
 293
 294   i = numTaps - 1u;
 295
 296   /* copy data */
 297   while(i > 0u)
 298   {
 299     *pStateCurnt++ = *pState++;
 300
 301     /* Decrement the loop counter */
 302     i--;
 303   }
 304
 305 #endif /*   #ifndef ARM_MATH_CM0_FAMILY */
 306
 307 }
 308
 309 /**
 310  * @} end of FIR_decimate group
 311  */