/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_iir_lattice_f32.c
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* Description: Floating-point IIR Lattice filter processing function
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*
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* $Date: 27. January 2017
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* $Revision: V.1.5.1
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*
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* Target Processor: Cortex-M cores
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* -------------------------------------------------------------------- */
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/*
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* Copyright (C) 2010-2017 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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#include "arm_math.h"
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/**
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* @ingroup groupFilters
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*/
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/**
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* @defgroup IIR_Lattice Infinite Impulse Response (IIR) Lattice Filters
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*
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* This set of functions implements lattice filters
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* for Q15, Q31 and floating-point data types. Lattice filters are used in a
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* variety of adaptive filter applications. The filter structure has feedforward and
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* feedback components and the net impulse response is infinite length.
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* The functions operate on blocks
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* of input and output data and each call to the function processes
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* <code>blockSize</code> samples through the filter. <code>pSrc</code> and
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* <code>pDst</code> point to input and output arrays containing <code>blockSize</code> values.
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* \par Algorithm:
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* \image html IIRLattice.gif "Infinite Impulse Response Lattice filter"
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* <pre>
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* fN(n) = x(n)
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* fm-1(n) = fm(n) - km * gm-1(n-1) for m = N, N-1, ...1
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* gm(n) = km * fm-1(n) + gm-1(n-1) for m = N, N-1, ...1
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* y(n) = vN * gN(n) + vN-1 * gN-1(n) + ...+ v0 * g0(n)
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* </pre>
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* \par
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* <code>pkCoeffs</code> points to array of reflection coefficients of size <code>numStages</code>.
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* Reflection coefficients are stored in time-reversed order.
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* \par
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* <pre>
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* {kN, kN-1, ....k1}
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* </pre>
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* <code>pvCoeffs</code> points to the array of ladder coefficients of size <code>(numStages+1)</code>.
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* Ladder coefficients are stored in time-reversed order.
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* \par
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* <pre>
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* {vN, vN-1, ...v0}
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* </pre>
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* <code>pState</code> points to a state array of size <code>numStages + blockSize</code>.
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* The state variables shown in the figure above (the g values) are stored in the <code>pState</code> array.
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* The state variables are updated after each block of data is processed; the coefficients are untouched.
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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 arrays cannot be shared.
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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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* To do this manually without calling the init function, assign the follow subfields of the instance structure:
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* numStages, pkCoeffs, pvCoeffs, pState. Also set all of the values in pState to zero.
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*
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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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* Set the values in the state buffer to zeros and then manually initialize the instance structure as follows:
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* <pre>
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*arm_iir_lattice_instance_f32 S = {numStages, pState, pkCoeffs, pvCoeffs};
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*arm_iir_lattice_instance_q31 S = {numStages, pState, pkCoeffs, pvCoeffs};
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*arm_iir_lattice_instance_q15 S = {numStages, pState, pkCoeffs, pvCoeffs};
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* </pre>
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* \par
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* where <code>numStages</code> is the number of stages in the filter; <code>pState</code> points to the state buffer array;
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* <code>pkCoeffs</code> points to array of the reflection coefficients; <code>pvCoeffs</code> points to the array of ladder coefficients.
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* \par Fixed-Point Behavior
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* Care must be taken when using the fixed-point versions of the IIR lattice 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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* @addtogroup IIR_Lattice
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* @{
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*/
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/**
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* @brief Processing function for the floating-point IIR lattice filter.
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* @param[in] *S points to an instance of the floating-point IIR lattice 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 samples to process.
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* @return none.
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*/
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#if defined (ARM_MATH_DSP)
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/* Run the below code for Cortex-M4 and Cortex-M3 */
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void arm_iir_lattice_f32(
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const arm_iir_lattice_instance_f32 * S,
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float32_t * pSrc,
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float32_t * pDst,
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uint32_t blockSize)
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{
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float32_t fnext1, gcurr1, gnext; /* Temporary variables for lattice stages */
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float32_t acc; /* Accumlator */
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uint32_t blkCnt, tapCnt; /* temporary variables for counts */
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float32_t *px1, *px2, *pk, *pv; /* temporary pointers for state and coef */
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uint32_t numStages = S->numStages; /* number of stages */
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float32_t *pState; /* State pointer */
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float32_t *pStateCurnt; /* State current pointer */
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float32_t k1, k2;
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float32_t v1, v2, v3, v4;
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float32_t gcurr2;
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float32_t fnext2;
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/* initialise loop count */
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blkCnt = blockSize;
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/* initialise state pointer */
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pState = &S->pState[0];
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/* Sample processing */
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while (blkCnt > 0U)
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{
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/* Read Sample from input buffer */
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/* fN(n) = x(n) */
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fnext2 = *pSrc++;
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/* Initialize Ladder coeff pointer */
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pv = &S->pvCoeffs[0];
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/* Initialize Reflection coeff pointer */
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pk = &S->pkCoeffs[0];
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/* Initialize state read pointer */
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px1 = pState;
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/* Initialize state write pointer */
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px2 = pState;
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/* Set accumulator to zero */
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acc = 0.0;
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/* Loop unrolling. Process 4 taps at a time. */
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tapCnt = (numStages) >> 2;
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while (tapCnt > 0U)
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{
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/* Read gN-1(n-1) from state buffer */
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gcurr1 = *px1;
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/* read reflection coefficient kN */
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k1 = *pk;
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/* fN-1(n) = fN(n) - kN * gN-1(n-1) */
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fnext1 = fnext2 - (k1 * gcurr1);
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/* read ladder coefficient vN */
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v1 = *pv;
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/* read next reflection coefficient kN-1 */
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k2 = *(pk + 1U);
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/* Read gN-2(n-1) from state buffer */
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gcurr2 = *(px1 + 1U);
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/* read next ladder coefficient vN-1 */
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v2 = *(pv + 1U);
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/* fN-2(n) = fN-1(n) - kN-1 * gN-2(n-1) */
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fnext2 = fnext1 - (k2 * gcurr2);
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/* gN(n) = kN * fN-1(n) + gN-1(n-1) */
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gnext = gcurr1 + (k1 * fnext1);
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/* read reflection coefficient kN-2 */
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k1 = *(pk + 2U);
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/* write gN(n) into state for next sample processing */
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*px2++ = gnext;
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/* Read gN-3(n-1) from state buffer */
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gcurr1 = *(px1 + 2U);
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/* y(n) += gN(n) * vN */
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acc += (gnext * v1);
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/* fN-3(n) = fN-2(n) - kN-2 * gN-3(n-1) */
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fnext1 = fnext2 - (k1 * gcurr1);
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/* gN-1(n) = kN-1 * fN-2(n) + gN-2(n-1) */
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gnext = gcurr2 + (k2 * fnext2);
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/* Read gN-4(n-1) from state buffer */
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gcurr2 = *(px1 + 3U);
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/* y(n) += gN-1(n) * vN-1 */
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acc += (gnext * v2);
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/* read reflection coefficient kN-3 */
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k2 = *(pk + 3U);
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/* write gN-1(n) into state for next sample processing */
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*px2++ = gnext;
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/* fN-4(n) = fN-3(n) - kN-3 * gN-4(n-1) */
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fnext2 = fnext1 - (k2 * gcurr2);
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/* gN-2(n) = kN-2 * fN-3(n) + gN-3(n-1) */
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gnext = gcurr1 + (k1 * fnext1);
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/* read ladder coefficient vN-2 */
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v3 = *(pv + 2U);
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/* y(n) += gN-2(n) * vN-2 */
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acc += (gnext * v3);
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/* write gN-2(n) into state for next sample processing */
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*px2++ = gnext;
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/* update pointer */
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pk += 4U;
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/* gN-3(n) = kN-3 * fN-4(n) + gN-4(n-1) */
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gnext = (fnext2 * k2) + gcurr2;
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/* read next ladder coefficient vN-3 */
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v4 = *(pv + 3U);
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/* y(n) += gN-4(n) * vN-4 */
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acc += (gnext * v4);
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/* write gN-3(n) into state for next sample processing */
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*px2++ = gnext;
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/* update pointers */
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px1 += 4U;
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pv += 4U;
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tapCnt--;
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}
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/* If the filter length is not a multiple of 4, compute the remaining filter taps */
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tapCnt = (numStages) % 0x4U;
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while (tapCnt > 0U)
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{
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gcurr1 = *px1++;
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/* Process sample for last taps */
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fnext1 = fnext2 - ((*pk) * gcurr1);
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gnext = (fnext1 * (*pk++)) + gcurr1;
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/* Output samples for last taps */
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acc += (gnext * (*pv++));
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*px2++ = gnext;
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fnext2 = fnext1;
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tapCnt--;
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}
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/* y(n) += g0(n) * v0 */
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acc += (fnext2 * (*pv));
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*px2++ = fnext2;
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/* write out into pDst */
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*pDst++ = acc;
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/* Advance the state pointer by 4 to process the next group of 4 samples */
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pState = pState + 1U;
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blkCnt--;
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}
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/* Processing is complete. Now copy last S->numStages samples to start of the buffer
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for the preperation of next frame process */
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/* Points to the start of the state buffer */
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pStateCurnt = &S->pState[0];
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pState = &S->pState[blockSize];
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tapCnt = numStages >> 2U;
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/* copy data */
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while (tapCnt > 0U)
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{
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*pStateCurnt++ = *pState++;
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*pStateCurnt++ = *pState++;
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*pStateCurnt++ = *pState++;
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*pStateCurnt++ = *pState++;
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/* Decrement the loop counter */
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tapCnt--;
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}
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/* Calculate remaining number of copies */
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tapCnt = (numStages) % 0x4U;
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/* Copy the remaining q31_t data */
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while (tapCnt > 0U)
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{
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*pStateCurnt++ = *pState++;
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/* Decrement the loop counter */
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tapCnt--;
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}
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}
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#else
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void arm_iir_lattice_f32(
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const arm_iir_lattice_instance_f32 * S,
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float32_t * pSrc,
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float32_t * pDst,
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uint32_t blockSize)
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{
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float32_t fcurr, fnext = 0, gcurr, gnext; /* Temporary variables for lattice stages */
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float32_t acc; /* Accumlator */
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uint32_t blkCnt, tapCnt; /* temporary variables for counts */
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float32_t *px1, *px2, *pk, *pv; /* temporary pointers for state and coef */
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uint32_t numStages = S->numStages; /* number of stages */
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float32_t *pState; /* State pointer */
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float32_t *pStateCurnt; /* State current pointer */
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/* Run the below code for Cortex-M0 */
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blkCnt = blockSize;
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pState = &S->pState[0];
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/* Sample processing */
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while (blkCnt > 0U)
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{
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/* Read Sample from input buffer */
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/* fN(n) = x(n) */
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fcurr = *pSrc++;
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/* Initialize state read pointer */
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px1 = pState;
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/* Initialize state write pointer */
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px2 = pState;
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/* Set accumulator to zero */
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acc = 0.0f;
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/* Initialize Ladder coeff pointer */
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pv = &S->pvCoeffs[0];
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/* Initialize Reflection coeff pointer */
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pk = &S->pkCoeffs[0];
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/* Process sample for numStages */
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tapCnt = numStages;
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while (tapCnt > 0U)
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{
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gcurr = *px1++;
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/* Process sample for last taps */
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fnext = fcurr - ((*pk) * gcurr);
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gnext = (fnext * (*pk++)) + gcurr;
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/* Output samples for last taps */
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acc += (gnext * (*pv++));
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*px2++ = gnext;
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fcurr = fnext;
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/* Decrementing loop counter */
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tapCnt--;
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}
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/* y(n) += g0(n) * v0 */
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acc += (fnext * (*pv));
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*px2++ = fnext;
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/* write out into pDst */
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*pDst++ = acc;
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/* Advance the state pointer by 1 to process the next group of samples */
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pState = pState + 1U;
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blkCnt--;
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}
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/* Processing is complete. Now copy last S->numStages samples to start of the buffer
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for the preperation of next frame process */
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/* Points to the start of the state buffer */
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pStateCurnt = &S->pState[0];
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pState = &S->pState[blockSize];
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tapCnt = numStages;
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/* Copy the data */
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while (tapCnt > 0U)
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{
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*pStateCurnt++ = *pState++;
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/* Decrement the loop counter */
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tapCnt--;
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}
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}
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#endif /* #if defined (ARM_MATH_DSP) */
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/**
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* @} end of IIR_Lattice group
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*/
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