| /* ---------------------------------------------------------------------- |
| * Project: CMSIS DSP Library |
| * Title: arm_iir_lattice_f32.c |
| * Description: Floating-point IIR Lattice filter processing function |
| * |
| * $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 |
| */ |
| |
| /** |
| @defgroup IIR_Lattice Infinite Impulse Response (IIR) Lattice Filters |
| |
| This set of functions implements lattice filters |
| for Q15, Q31 and floating-point data types. Lattice filters are used in a |
| variety of adaptive filter applications. The filter structure has feedforward and |
| feedback components and the net impulse response is infinite length. |
| The functions operate on blocks |
| of input and output data and each call to the function processes |
| <code>blockSize</code> samples through the filter. <code>pSrc</code> and |
| <code>pDst</code> point to input and output arrays containing <code>blockSize</code> values. |
| |
| @par Algorithm |
| \image html IIRLattice.gif "Infinite Impulse Response Lattice filter" |
| @par |
| <pre> |
| fN(n) = x(n) |
| fm-1(n) = fm(n) - km * gm-1(n-1) for m = N, N-1, ..., 1 |
| gm(n) = km * fm-1(n) + gm-1(n-1) for m = N, N-1, ..., 1 |
| y(n) = vN * gN(n) + vN-1 * gN-1(n) + ...+ v0 * g0(n) |
| </pre> |
| @par |
| <code>pkCoeffs</code> points to array of reflection coefficients of size <code>numStages</code>. |
| Reflection Coefficients are stored in time-reversed order. |
| @par |
| <pre> |
| {kN, kN-1, ..., k1} |
| </pre> |
| @par |
| <code>pvCoeffs</code> points to the array of ladder coefficients of size <code>(numStages+1)</code>. |
| Ladder coefficients are stored in time-reversed order. |
| <pre> |
| {vN, vN-1, ..., v0} |
| </pre> |
| @par |
| <code>pState</code> points to a state array of size <code>numStages + blockSize</code>. |
| The state variables shown in the figure above (the g values) are stored in the <code>pState</code> array. |
| The state variables are updated after each block of data is processed; the coefficients are untouched. |
| |
| @par Instance Structure |
| The coefficients and state variables for a filter are stored together in an instance data structure. |
| A separate instance structure must be defined for each filter. |
| Coefficient arrays may be shared among several instances while state variable arrays cannot be shared. |
| There are separate instance structure declarations for each of the 3 supported data types. |
| |
| @par Initialization Functions |
| There is also an associated initialization function for each data type. |
| The initialization function performs the following operations: |
| - Sets the values of the internal structure fields. |
| - Zeros out the values in the state buffer. |
| To do this manually without calling the init function, assign the follow subfields of the instance structure: |
| numStages, pkCoeffs, pvCoeffs, pState. Also set all of the values in pState to zero. |
| @par |
| Use of the initialization function is optional. |
| However, if the initialization function is used, then the instance structure cannot be placed into a const data section. |
| To place an instance structure into a const data section, the instance structure must be manually initialized. |
| Set the values in the state buffer to zeros and then manually initialize the instance structure as follows: |
| <pre> |
| arm_iir_lattice_instance_f32 S = {numStages, pState, pkCoeffs, pvCoeffs}; |
| arm_iir_lattice_instance_q31 S = {numStages, pState, pkCoeffs, pvCoeffs}; |
| arm_iir_lattice_instance_q15 S = {numStages, pState, pkCoeffs, pvCoeffs}; |
| </pre> |
| @par |
| where <code>numStages</code> is the number of stages in the filter; <code>pState</code> points to the state buffer array; |
| <code>pkCoeffs</code> points to array of the reflection coefficients; <code>pvCoeffs</code> points to the array of ladder coefficients. |
| |
| @par Fixed-Point Behavior |
| Care must be taken when using the fixed-point versions of the IIR lattice filter functions. |
| In particular, the overflow and saturation behavior of the accumulator used in each function must be considered. |
| Refer to the function specific documentation below for usage guidelines. |
| */ |
| |
| /** |
| @addtogroup IIR_Lattice |
| @{ |
| */ |
| |
| /** |
| @brief Processing function for the floating-point IIR lattice filter. |
| @param[in] S points to an instance of the floating-point IIR lattice 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 |
| @return none |
| */ |
| |
| void arm_iir_lattice_f32( |
| const arm_iir_lattice_instance_f32 * S, |
| const float32_t * pSrc, |
| float32_t * pDst, |
| uint32_t blockSize) |
| { |
| float32_t *pState = S->pState; /* State pointer */ |
| float32_t *pStateCur; /* State current pointer */ |
| float32_t acc; /* Accumlator */ |
| float32_t fnext1, fnext2, gcurr1, gnext; /* Temporary variables for lattice stages */ |
| float32_t *px1, *px2, *pk, *pv; /* Temporary pointers for state and coef */ |
| uint32_t numStages = S->numStages; /* Number of stages */ |
| uint32_t blkCnt, tapCnt; /* Temporary variables for counts */ |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| float32_t gcurr2; /* Temporary variables for lattice stages */ |
| float32_t k1, k2; |
| float32_t v1, v2, v3, v4; |
| #endif |
| |
| /* initialise loop count */ |
| blkCnt = blockSize; |
| |
| /* Sample processing */ |
| while (blkCnt > 0U) |
| { |
| /* Read Sample from input buffer */ |
| /* fN(n) = x(n) */ |
| fnext2 = *pSrc++; |
| |
| /* Initialize Ladder coeff pointer */ |
| pv = &S->pvCoeffs[0]; |
| |
| /* Initialize Reflection coeff pointer */ |
| pk = &S->pkCoeffs[0]; |
| |
| /* Initialize state read pointer */ |
| px1 = pState; |
| |
| /* Initialize state write pointer */ |
| px2 = pState; |
| |
| /* Set accumulator to zero */ |
| acc = 0.0; |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| |
| /* Loop unrolling: Compute 4 taps at a time. */ |
| tapCnt = (numStages) >> 2U; |
| |
| while (tapCnt > 0U) |
| { |
| /* Read gN-1(n-1) from state buffer */ |
| gcurr1 = *px1; |
| |
| /* read reflection coefficient kN */ |
| k1 = *pk; |
| |
| /* fN-1(n) = fN(n) - kN * gN-1(n-1) */ |
| fnext1 = fnext2 - (k1 * gcurr1); |
| |
| /* read ladder coefficient vN */ |
| v1 = *pv; |
| |
| /* read next reflection coefficient kN-1 */ |
| k2 = *(pk + 1U); |
| |
| /* Read gN-2(n-1) from state buffer */ |
| gcurr2 = *(px1 + 1U); |
| |
| /* read next ladder coefficient vN-1 */ |
| v2 = *(pv + 1U); |
| |
| /* fN-2(n) = fN-1(n) - kN-1 * gN-2(n-1) */ |
| fnext2 = fnext1 - (k2 * gcurr2); |
| |
| /* gN(n) = kN * fN-1(n) + gN-1(n-1) */ |
| gnext = gcurr1 + (k1 * fnext1); |
| |
| /* read reflection coefficient kN-2 */ |
| k1 = *(pk + 2U); |
| |
| /* write gN(n) into state for next sample processing */ |
| *px2++ = gnext; |
| |
| /* Read gN-3(n-1) from state buffer */ |
| gcurr1 = *(px1 + 2U); |
| |
| /* y(n) += gN(n) * vN */ |
| acc += (gnext * v1); |
| |
| /* fN-3(n) = fN-2(n) - kN-2 * gN-3(n-1) */ |
| fnext1 = fnext2 - (k1 * gcurr1); |
| |
| /* gN-1(n) = kN-1 * fN-2(n) + gN-2(n-1) */ |
| gnext = gcurr2 + (k2 * fnext2); |
| |
| /* Read gN-4(n-1) from state buffer */ |
| gcurr2 = *(px1 + 3U); |
| |
| /* y(n) += gN-1(n) * vN-1 */ |
| acc += (gnext * v2); |
| |
| /* read reflection coefficient kN-3 */ |
| k2 = *(pk + 3U); |
| |
| /* write gN-1(n) into state for next sample processing */ |
| *px2++ = gnext; |
| |
| /* fN-4(n) = fN-3(n) - kN-3 * gN-4(n-1) */ |
| fnext2 = fnext1 - (k2 * gcurr2); |
| |
| /* gN-2(n) = kN-2 * fN-3(n) + gN-3(n-1) */ |
| gnext = gcurr1 + (k1 * fnext1); |
| |
| /* read ladder coefficient vN-2 */ |
| v3 = *(pv + 2U); |
| |
| /* y(n) += gN-2(n) * vN-2 */ |
| acc += (gnext * v3); |
| |
| /* write gN-2(n) into state for next sample processing */ |
| *px2++ = gnext; |
| |
| /* update pointer */ |
| pk += 4U; |
| |
| /* gN-3(n) = kN-3 * fN-4(n) + gN-4(n-1) */ |
| gnext = (fnext2 * k2) + gcurr2; |
| |
| /* read next ladder coefficient vN-3 */ |
| v4 = *(pv + 3U); |
| |
| /* y(n) += gN-4(n) * vN-4 */ |
| acc += (gnext * v4); |
| |
| /* write gN-3(n) into state for next sample processing */ |
| *px2++ = gnext; |
| |
| /* update pointers */ |
| px1 += 4U; |
| pv += 4U; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| /* Loop unrolling: Compute remaining taps */ |
| tapCnt = numStages % 0x4U; |
| |
| #else |
| |
| /* Initialize tapCnt with number of samples */ |
| tapCnt = numStages; |
| |
| #endif /* #if defined (ARM_MATH_LOOPUNROLL) */ |
| |
| while (tapCnt > 0U) |
| { |
| gcurr1 = *px1++; |
| /* Process sample for last taps */ |
| fnext1 = fnext2 - ((*pk) * gcurr1); |
| gnext = (fnext1 * (*pk++)) + gcurr1; |
| /* Output samples for last taps */ |
| acc += (gnext * (*pv++)); |
| *px2++ = gnext; |
| fnext2 = fnext1; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| /* y(n) += g0(n) * v0 */ |
| acc += (fnext2 * (*pv)); |
| |
| *px2++ = fnext2; |
| |
| /* write out into pDst */ |
| *pDst++ = acc; |
| |
| /* Advance the state pointer by 4 to process the next group of 4 samples */ |
| pState = pState + 1U; |
| |
| /* Decrement loop counter */ |
| blkCnt--; |
| } |
| |
| /* Processing is complete. Now copy last S->numStages samples to start of the buffer |
| for the preperation of next frame process */ |
| |
| /* Points to the start of the state buffer */ |
| pStateCur = &S->pState[0]; |
| pState = &S->pState[blockSize]; |
| |
| /* Copy data */ |
| #if defined (ARM_MATH_LOOPUNROLL) |
| |
| /* Loop unrolling: Compute 4 taps at a time. */ |
| tapCnt = numStages >> 2U; |
| |
| while (tapCnt > 0U) |
| { |
| *pStateCur++ = *pState++; |
| *pStateCur++ = *pState++; |
| *pStateCur++ = *pState++; |
| *pStateCur++ = *pState++; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| /* Loop unrolling: Compute remaining taps */ |
| tapCnt = numStages % 0x4U; |
| |
| #else |
| |
| /* Initialize blkCnt with number of samples */ |
| tapCnt = numStages; |
| |
| #endif /* #if defined (ARM_MATH_LOOPUNROLL) */ |
| |
| while (tapCnt > 0U) |
| { |
| *pStateCur++ = *pState++; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| } |
| |
| /** |
| @} end of IIR_Lattice group |
| */ |