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+/* ----------------------------------------------------------------------
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+ * Project: CMSIS DSP Library
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+ * Title: arm_fir_decimate_f64.c
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+ * Description: FIR decimation for floating-point sequences
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+ *
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+ * $Date: 17 February 2024
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+ * $Revision: V1.16.0
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+ *
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+ * Target Processor: Cortex-M and Cortex-A cores
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+ * -------------------------------------------------------------------- */
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+/*
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+ * Copyright (C) 2010-2024 ARM Limited or its affiliates. All rights reserved.
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+ *
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+ * SPDX-License-Identifier: Apache-2.0
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+ *
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+ * Licensed under the Apache License, Version 2.0 (the License); you may
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+ * not use this file except in compliance with the License.
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+ * You may obtain a copy of the License at
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+ *
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+ * www.apache.org/licenses/LICENSE-2.0
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+ *
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+ * Unless required by applicable law or agreed to in writing, software
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+ * distributed under the License is distributed on an AS IS BASIS, WITHOUT
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+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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+ * See the License for the specific language governing permissions and
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+ * limitations under the License.
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+ */
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+
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+#include "dsp/filtering_functions.h"
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+
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+/**
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+ @ingroup groupFilters
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+ */
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+
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+/**
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+ @defgroup FIR_decimate Finite Impulse Response (FIR) Decimator
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+
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+ These functions combine an FIR filter together with a decimator.
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+ They are used in multirate systems for reducing the sample rate of a signal without introducing aliasing distortion.
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+ Conceptually, the functions are equivalent to the block diagram below:
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+ \image html FIRDecimator.gif "Components included in the FIR Decimator functions"
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+ When decimating by a factor of <code>M</code>, the signal should be prefiltered by a lowpass filter with a normalized
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+ cutoff frequency of <code>1/M</code> in order to prevent aliasing distortion.
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+ The user of the function is responsible for providing the filter coefficients.
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+
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+ The FIR decimator functions provided in the CMSIS DSP Library combine the FIR filter and the decimator in an efficient manner.
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+ Instead of calculating all of the FIR filter outputs and discarding <code>M-1</code> out of every <code>M</code>, only the
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+ samples output by the decimator are computed.
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+ The functions operate on blocks of input and output data.
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+ <code>pSrc</code> points to an array of <code>blockSize</code> input values and
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+ <code>pDst</code> points to an array of <code>blockSize/M</code> output values.
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+ In order to have an integer number of output samples <code>blockSize</code>
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+ must always be a multiple of the decimation factor <code>M</code>.
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+
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+ The library provides separate functions for Q15, Q31 and floating-point data types.
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+
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+ @par Algorithm:
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+ The FIR portion of the algorithm uses the standard form filter:
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+ <pre>
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+ y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1]
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+ </pre>
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+ where, <code>b[n]</code> are the filter coefficients.
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+ @par
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+ The <code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>.
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+ Coefficients are stored in time reversed order.
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+ @par
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+ <pre>
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+ {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
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+ </pre>
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+ @par
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+ <code>pState</code> points to a state array of size <code>numTaps + blockSize - 1</code>.
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+ Samples in the state buffer are stored in the order:
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+ @par
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+ <pre>
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+ {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]}
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+ </pre>
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+ The state variables are updated after each block of data is processed, the coefficients are untouched.
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+
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+ @par Instance Structure
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+ The coefficients and state variables for a filter are stored together in an instance data structure.
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+ A separate instance structure must be defined for each filter.
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+ Coefficient arrays may be shared among several instances while state variable array should be allocated separately.
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+ There are separate instance structure declarations for each of the 3 supported data types.
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+
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+ @par Initialization Functions
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+ There is also an associated initialization function for each data type.
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+ The initialization function performs the following operations:
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+ - Sets the values of the internal structure fields.
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+ - Zeros out the values in the state buffer.
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+ - Checks to make sure that the size of the input is a multiple of the decimation factor.
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+ To do this manually without calling the init function, assign the follow subfields of the instance structure:
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+ numTaps, pCoeffs, M (decimation factor), pState. Also set all of the values in pState to zero.
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+ @par
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+ Use of the initialization function is optional.
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+ However, if the initialization function is used, then the instance structure cannot be placed into a const data section.
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+ To place an instance structure into a const data section, the instance structure must be manually initialized.
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+ The code below statically initializes each of the 3 different data type filter instance structures
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+ <pre>
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+ arm_fir_decimate_instance_f64 S = {M, numTaps, pCoeffs, pState};
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+ arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState};
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+ arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState};
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+ </pre>
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+ where <code>M</code> is the decimation factor; <code>numTaps</code> is the number of filter coefficients in the filter;
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+ <code>pCoeffs</code> is the address of the coefficient buffer;
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+ <code>pState</code> is the address of the state buffer.
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+ Be sure to set the values in the state buffer to zeros when doing static initialization.
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+
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+ @par Fixed-Point Behavior
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+ Care must be taken when using the fixed-point versions of the FIR decimate filter functions.
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+ In particular, the overflow and saturation behavior of the accumulator used in each function must be considered.
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+ Refer to the function specific documentation below for usage guidelines.
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+ */
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+
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+/**
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+ @addtogroup FIR_decimate
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+ @{
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+ */
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+
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+/**
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+ @brief Processing function for floating-point FIR decimator.
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+ @param[in] S points to an instance of the floating-point FIR decimator structure
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+ @param[in] pSrc points to the block of input data
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+ @param[out] pDst points to the block of output data
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+ @param[in] blockSize number of input samples to process
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+ */
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+
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+void arm_fir_decimate_f64(
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+ const arm_fir_decimate_instance_f64 * S,
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+ const float64_t * pSrc,
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+ float64_t * pDst,
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+ uint32_t blockSize)
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+{
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+ float64_t *pState = S->pState; /* State pointer */
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+ const float64_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
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+ float64_t *pStateCur; /* Points to the current sample of the state */
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+ float64_t *px0; /* Temporary pointer for state buffer */
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+ const float64_t *pb; /* Temporary pointer for coefficient buffer */
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+ float64_t x0, c0; /* Temporary variables to hold state and coefficient values */
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+ float64_t acc0; /* Accumulator */
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+ uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */
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+ uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */
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+
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+#if defined (ARM_MATH_LOOPUNROLL)
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+ float64_t *px1, *px2, *px3;
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+ float64_t x1, x2, x3;
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+ float64_t acc1, acc2, acc3;
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+#endif
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+
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+ /* S->pState buffer contains previous frame (numTaps - 1) samples */
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+ /* pStateCur points to the location where the new input data should be written */
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+ pStateCur = S->pState + (numTaps - 1U);
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+
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+#if defined (ARM_MATH_LOOPUNROLL)
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+
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+ /* Loop unrolling: Compute 4 samples at a time */
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+ blkCnt = outBlockSize >> 2U;
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+
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+ /* Samples loop unrolled by 4 */
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+ while (blkCnt > 0U)
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+ {
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+ /* Copy 4 * decimation factor number of new input samples into the state buffer */
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+ i = S->M * 4;
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+
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+ do
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+ {
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+ *pStateCur++ = *pSrc++;
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+
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+ } while (--i);
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+
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+ /* Set accumulators to zero */
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+ acc0 = 0.0f;
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+ acc1 = 0.0f;
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+ acc2 = 0.0f;
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+ acc3 = 0.0f;
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+
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+ /* Initialize state pointer for all the samples */
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+ px0 = pState;
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+ px1 = pState + S->M;
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+ px2 = pState + 2 * S->M;
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+ px3 = pState + 3 * S->M;
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+
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+ /* Initialize coeff pointer */
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+ pb = pCoeffs;
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+
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+ /* Loop unrolling: Compute 4 taps at a time */
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+ tapCnt = numTaps >> 2U;
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+
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+ while (tapCnt > 0U)
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+ {
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+ /* Read the b[numTaps-1] coefficient */
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+ c0 = *(pb++);
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+
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+ /* Read x[n-numTaps-1] sample for acc0 */
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+ x0 = *(px0++);
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+ /* Read x[n-numTaps-1] sample for acc1 */
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+ x1 = *(px1++);
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+ /* Read x[n-numTaps-1] sample for acc2 */
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+ x2 = *(px2++);
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+ /* Read x[n-numTaps-1] sample for acc3 */
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+ x3 = *(px3++);
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+
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+ /* Perform the multiply-accumulate */
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+ acc0 += x0 * c0;
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+ acc1 += x1 * c0;
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+ acc2 += x2 * c0;
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+ acc3 += x3 * c0;
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+
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+ /* Read the b[numTaps-2] coefficient */
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+ c0 = *(pb++);
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+
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+ /* Read x[n-numTaps-2] sample for acc0, acc1, acc2, acc3 */
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+ x0 = *(px0++);
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+ x1 = *(px1++);
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+ x2 = *(px2++);
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+ x3 = *(px3++);
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+
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+ /* Perform the multiply-accumulate */
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+ acc0 += x0 * c0;
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+ acc1 += x1 * c0;
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+ acc2 += x2 * c0;
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+ acc3 += x3 * c0;
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+
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+ /* Read the b[numTaps-3] coefficient */
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+ c0 = *(pb++);
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+
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+ /* Read x[n-numTaps-3] sample acc0, acc1, acc2, acc3 */
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+ x0 = *(px0++);
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+ x1 = *(px1++);
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+ x2 = *(px2++);
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+ x3 = *(px3++);
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+
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+ /* Perform the multiply-accumulate */
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+ acc0 += x0 * c0;
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+ acc1 += x1 * c0;
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+ acc2 += x2 * c0;
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+ acc3 += x3 * c0;
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+
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+ /* Read the b[numTaps-4] coefficient */
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+ c0 = *(pb++);
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+
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+ /* Read x[n-numTaps-4] sample acc0, acc1, acc2, acc3 */
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+ x0 = *(px0++);
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+ x1 = *(px1++);
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+ x2 = *(px2++);
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+ x3 = *(px3++);
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+
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+ /* Perform the multiply-accumulate */
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+ acc0 += x0 * c0;
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+ acc1 += x1 * c0;
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+ acc2 += x2 * c0;
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+ acc3 += x3 * c0;
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+
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+ /* Decrement loop counter */
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+ tapCnt--;
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+ }
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+
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+ /* Loop unrolling: Compute remaining taps */
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+ tapCnt = numTaps % 0x4U;
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+
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+ while (tapCnt > 0U)
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+ {
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+ /* Read coefficients */
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+ c0 = *(pb++);
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+
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+ /* Fetch state variables for acc0, acc1, acc2, acc3 */
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+ x0 = *(px0++);
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+ x1 = *(px1++);
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+ x2 = *(px2++);
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+ x3 = *(px3++);
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+
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+ /* Perform the multiply-accumulate */
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+ acc0 += x0 * c0;
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+ acc1 += x1 * c0;
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+ acc2 += x2 * c0;
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+ acc3 += x3 * c0;
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+
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+ /* Decrement loop counter */
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+ tapCnt--;
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+ }
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+
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+ /* Advance the state pointer by the decimation factor
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+ * to process the next group of decimation factor number samples */
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+ pState = pState + S->M * 4;
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+
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+ /* The result is in the accumulator, store in the destination buffer. */
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+ *pDst++ = acc0;
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+ *pDst++ = acc1;
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+ *pDst++ = acc2;
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+ *pDst++ = acc3;
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+
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+ /* Decrement loop counter */
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+ blkCnt--;
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+ }
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+
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+ /* Loop unrolling: Compute remaining samples */
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+ blkCnt = outBlockSize % 0x4U;
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+
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+#else
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+
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+ /* Initialize blkCnt with number of samples */
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+ blkCnt = outBlockSize;
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+
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+#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
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+
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+ while (blkCnt > 0U)
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+ {
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+ /* Copy decimation factor number of new input samples into the state buffer */
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+ i = S->M;
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+
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+ do
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+ {
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+ *pStateCur++ = *pSrc++;
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+
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+ } while (--i);
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+
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+ /* Set accumulator to zero */
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+ acc0 = 0.0f;
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+
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+ /* Initialize state pointer */
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+ px0 = pState;
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+
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+ /* Initialize coeff pointer */
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+ pb = pCoeffs;
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+
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+#if defined (ARM_MATH_LOOPUNROLL)
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+
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+ /* Loop unrolling: Compute 4 taps at a time */
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+ tapCnt = numTaps >> 2U;
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+
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+ while (tapCnt > 0U)
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+ {
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+ /* Read the b[numTaps-1] coefficient */
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+ c0 = *pb++;
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+
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+ /* Read x[n-numTaps-1] sample */
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+ x0 = *px0++;
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+
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+ /* Perform the multiply-accumulate */
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+ acc0 += x0 * c0;
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+
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+ /* Read the b[numTaps-2] coefficient */
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+ c0 = *pb++;
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+
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+ /* Read x[n-numTaps-2] sample */
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+ x0 = *px0++;
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+
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+ /* Perform the multiply-accumulate */
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+ acc0 += x0 * c0;
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+
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+ /* Read the b[numTaps-3] coefficient */
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+ c0 = *pb++;
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+
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+ /* Read x[n-numTaps-3] sample */
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+ x0 = *px0++;
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+
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+ /* Perform the multiply-accumulate */
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+ acc0 += x0 * c0;
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+
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+ /* Read the b[numTaps-4] coefficient */
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+ c0 = *pb++;
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+
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+ /* Read x[n-numTaps-4] sample */
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+ x0 = *px0++;
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+
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+ /* Perform the multiply-accumulate */
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+ acc0 += x0 * c0;
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+
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+ /* Decrement loop counter */
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+ tapCnt--;
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+ }
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+
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+ /* Loop unrolling: Compute remaining taps */
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+ tapCnt = numTaps % 0x4U;
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+
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+#else
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+
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+ /* Initialize tapCnt with number of taps */
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+ tapCnt = numTaps;
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+
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+#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
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+
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+ while (tapCnt > 0U)
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+ {
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+ /* Read coefficients */
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+ c0 = *pb++;
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+
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+ /* Fetch 1 state variable */
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+ x0 = *px0++;
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+
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+ /* Perform the multiply-accumulate */
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+ acc0 += x0 * c0;
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+
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+ /* Decrement loop counter */
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+ tapCnt--;
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+ }
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+
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+ /* Advance the state pointer by the decimation factor
|
|
|
+ * to process the next group of decimation factor number samples */
|
|
|
+ pState = pState + S->M;
|
|
|
+
|
|
|
+ /* The result is in the accumulator, store in the destination buffer. */
|
|
|
+ *pDst++ = acc0;
|
|
|
+
|
|
|
+ /* Decrement loop counter */
|
|
|
+ blkCnt--;
|
|
|
+ }
|
|
|
+
|
|
|
+ /* Processing is complete.
|
|
|
+ Now copy the last numTaps - 1 samples to the satrt of the state buffer.
|
|
|
+ This prepares the state buffer for the next function call. */
|
|
|
+
|
|
|
+ /* Points to the start of the state buffer */
|
|
|
+ pStateCur = S->pState;
|
|
|
+
|
|
|
+#if defined (ARM_MATH_LOOPUNROLL)
|
|
|
+
|
|
|
+ /* Loop unrolling: Compute 4 taps at a time */
|
|
|
+ tapCnt = (numTaps - 1U) >> 2U;
|
|
|
+
|
|
|
+ /* Copy data */
|
|
|
+ while (tapCnt > 0U)
|
|
|
+ {
|
|
|
+ *pStateCur++ = *pState++;
|
|
|
+ *pStateCur++ = *pState++;
|
|
|
+ *pStateCur++ = *pState++;
|
|
|
+ *pStateCur++ = *pState++;
|
|
|
+
|
|
|
+ /* Decrement loop counter */
|
|
|
+ tapCnt--;
|
|
|
+ }
|
|
|
+
|
|
|
+ /* Loop unrolling: Compute remaining taps */
|
|
|
+ tapCnt = (numTaps - 1U) % 0x04U;
|
|
|
+
|
|
|
+#else
|
|
|
+
|
|
|
+ /* Initialize tapCnt with number of taps */
|
|
|
+ tapCnt = (numTaps - 1U);
|
|
|
+
|
|
|
+#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
|
|
|
+
|
|
|
+ /* Copy data */
|
|
|
+ while (tapCnt > 0U)
|
|
|
+ {
|
|
|
+ *pStateCur++ = *pState++;
|
|
|
+
|
|
|
+ /* Decrement loop counter */
|
|
|
+ tapCnt--;
|
|
|
+ }
|
|
|
+
|
|
|
+}
|
|
|
+/**
|
|
|
+ @} end of FIR_decimate group
|
|
|
+ */
|
Christophe Favergeon