DSP/Source/FilteringFunctions/arm_biquad_cascade_df1_fast_q15.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_biquad_cascade_df1_fast_q15.c
 * Description:  Fast processing function for the Q15 Biquad cascade filter
 *
 * $Date:        18. March 2019
 * $Revision:    V1.6.0
 *
 * Target Processor: Cortex-M cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "arm_math.h"

/**
  @ingroup groupFilters
 */

/**
  @addtogroup BiquadCascadeDF1
  @{
 */

/**
  @brief         Processing function for the Q15 Biquad cascade filter (fast variant).
  @param[in]     S         points to an instance of the Q15 Biquad cascade structure
  @param[in]     pSrc      points to the block of input data
  @param[out]    pDst      points to the block of output data
  @param[in]     blockSize number of samples to process per call
  @return        none

  @par           Scaling and Overflow Behavior
                   This fast version uses a 32-bit accumulator with 2.30 format.
                   The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit.
                   Thus, if the accumulator result overflows it wraps around and distorts the result.
                   In order to avoid overflows completely the input signal must be scaled down by two bits and lie in the range [-0.25 +0.25).
                   The 2.30 accumulator is then shifted by <code>postShift</code> bits and the result truncated to 1.15 format by discarding the low 16 bits.
 @remark
                   Refer to \ref arm_biquad_cascade_df1_q15() for a slower implementation of this function
                   which uses 64-bit accumulation to avoid wrap around distortion. Both the slow and the fast versions use the same instance structure.
                   Use the function \ref arm_biquad_cascade_df1_init_q15() to initialize the filter structure.
 */

void arm_biquad_cascade_df1_fast_q15(
  const arm_biquad_casd_df1_inst_q15 * S,
  const q15_t * pSrc,
        q15_t * pDst,
        uint32_t blockSize)
{
  const q15_t *pIn = pSrc;                             /* Source pointer */
        q15_t *pOut = pDst;                            /* Destination pointer */
        q15_t *pState = S->pState;                     /* State pointer */
  const q15_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
        q31_t acc;                                     /* Accumulator */
        q31_t in;                                      /* Temporary variable to hold input value */
        q31_t out;                                     /* Temporary variable to hold output value */
        q31_t b0;                                      /* Temporary variable to hold bo value */
        q31_t b1, a1;                                  /* Filter coefficients */
        q31_t state_in, state_out;                     /* Filter state variables */
        int32_t shift = (int32_t) (15 - S->postShift); /* Post shift */
        uint32_t sample, stage = S->numStages;         /* Loop counters */

  do
  {
    /* Read the b0 and 0 coefficients using SIMD  */
    b0 = read_q15x2_ia ((q15_t **) &pCoeffs);

    /* Read the b1 and b2 coefficients using SIMD */
    b1 = read_q15x2_ia ((q15_t **) &pCoeffs);

    /* Read the a1 and a2 coefficients using SIMD */
    a1 = read_q15x2_ia ((q15_t **) &pCoeffs);

    /* Read the input state values from the state buffer:  x[n-1], x[n-2] */
    state_in = read_q15x2_ia (&pState);

    /* Read the output state values from the state buffer:  y[n-1], y[n-2] */
    state_out = read_q15x2_da (&pState);

#if defined (ARM_MATH_LOOPUNROLL)

    /* Apply loop unrolling and compute 2 output values simultaneously. */
    /* Variable acc hold output values that are being computed:
     *
     * acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
     * acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
     */

    /* Loop unrolling: Compute 2 outputs at a time */
    sample = blockSize >> 1U;

    while (sample > 0U)
    {

      /* Read the input */
      in = read_q15x2_ia ((q15_t **) &pIn);

      /* out =  b0 * x[n] + 0 * 0 */
      out = __SMUAD(b0, in);
      /* acc =  b1 * x[n-1] + acc +=  b2 * x[n-2] + out */
      acc = __SMLAD(b1, state_in, out);
      /* acc +=  a1 * y[n-1] + acc +=  a2 * y[n-2] */
      acc = __SMLAD(a1, state_out, acc);

      /* The result is converted from 3.29 to 1.31 and then saturation is applied */
      out = __SSAT((acc >> shift), 16);

      /* Every time after the output is computed state should be updated. */
      /* The states should be updated as:  */
      /* Xn2 = Xn1 */
      /* Xn1 = Xn  */
      /* Yn2 = Yn1 */
      /* Yn1 = acc */
      /* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
      /* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */

#ifndef  ARM_MATH_BIG_ENDIAN
      state_in  = __PKHBT(in, state_in, 16);
      state_out = __PKHBT(out, state_out, 16);
#else
      state_in  = __PKHBT(state_in >> 16, (in >> 16), 16);
      state_out = __PKHBT(state_out >> 16, (out), 16);
#endif /* #ifndef  ARM_MATH_BIG_ENDIAN */

      /* out =  b0 * x[n] + 0 * 0 */
      out = __SMUADX(b0, in);
      /* acc0 =  b1 * x[n-1] , acc0 +=  b2 * x[n-2] + out */
      acc = __SMLAD(b1, state_in, out);
      /* acc +=  a1 * y[n-1] + acc +=  a2 * y[n-2] */
      acc = __SMLAD(a1, state_out, acc);

      /* The result is converted from 3.29 to 1.31 and then saturation is applied */
      out = __SSAT((acc >> shift), 16);

      /* Store the output in the destination buffer. */
#ifndef  ARM_MATH_BIG_ENDIAN
      write_q15x2_ia (&pOut, __PKHBT(state_out, out, 16));
#else
      write_q15x2_ia (&pOut, __PKHBT(out, state_out >> 16, 16));
#endif /* #ifndef  ARM_MATH_BIG_ENDIAN */

      /* Every time after the output is computed state should be updated. */
      /* The states should be updated as:  */
      /* Xn2 = Xn1 */
      /* Xn1 = Xn  */
      /* Yn2 = Yn1 */
      /* Yn1 = acc */
      /* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
      /* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
#ifndef  ARM_MATH_BIG_ENDIAN
      state_in  = __PKHBT(in >> 16, state_in, 16);
      state_out = __PKHBT(out, state_out, 16);
#else
      state_in  = __PKHBT(state_in >> 16, in, 16);
      state_out = __PKHBT(state_out >> 16, out, 16);
#endif /* #ifndef  ARM_MATH_BIG_ENDIAN */

      /* Decrement loop counter */
      sample--;
    }

    /* Loop unrolling: Compute remaining outputs */
    sample = (blockSize & 0x1U);

#else

    /* Initialize blkCnt with number of samples */
    sample = blockSize;

#endif /* #if defined (ARM_MATH_LOOPUNROLL) */

    while (sample > 0U)
    {
      /* Read the input */
      in = *pIn++;

      /* out =  b0 * x[n] + 0 * 0 */
#ifndef  ARM_MATH_BIG_ENDIAN
      out = __SMUAD(b0, in);
#else
      out = __SMUADX(b0, in);
#endif /* #ifndef  ARM_MATH_BIG_ENDIAN */

      /* acc =  b1 * x[n-1], acc +=  b2 * x[n-2] + out */
      acc = __SMLAD(b1, state_in, out);
      /* acc +=  a1 * y[n-1] + acc +=  a2 * y[n-2] */
      acc = __SMLAD(a1, state_out, acc);

      /* The result is converted from 3.29 to 1.31 and then saturation is applied */
      out = __SSAT((acc >> shift), 16);

      /* Store the output in the destination buffer. */
      *pOut++ = (q15_t) out;

      /* Every time after the output is computed state should be updated. */
      /* The states should be updated as:  */
      /* Xn2 = Xn1 */
      /* Xn1 = Xn  */
      /* Yn2 = Yn1 */
      /* Yn1 = acc */
      /* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
      /* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
#ifndef  ARM_MATH_BIG_ENDIAN
      state_in = __PKHBT(in, state_in, 16);
      state_out = __PKHBT(out, state_out, 16);
#else
      state_in = __PKHBT(state_in >> 16, in, 16);
      state_out = __PKHBT(state_out >> 16, out, 16);
#endif /* #ifndef  ARM_MATH_BIG_ENDIAN */

      /* decrement loop counter */
      sample--;
    }

    /* The first stage goes from the input buffer to the output buffer. */
    /* Subsequent (numStages - 1) occur in-place in the output buffer */
    pIn = pDst;

    /* Reset the output pointer */
    pOut = pDst;

    /* Store the updated state variables back into the state array */
    write_q15x2_ia(&pState, state_in);
    write_q15x2_ia(&pState, state_out);

    /* Decrement loop counter */
    stage--;

  } while (stage > 0U);
}

/**
  @} end of BiquadCascadeDF1 group
 */