| /* ---------------------------------------------------------------------- |
| * Project: CMSIS DSP Library |
| * Title: arm_fir_lattice_f32.c |
| * Description: Processing function for floating-point FIR Lattice 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 |
| */ |
| |
| /** |
| @defgroup FIR_Lattice Finite Impulse Response (FIR) Lattice Filters |
| |
| This set of functions implements Finite Impulse Response (FIR) lattice filters |
| for Q15, Q31 and floating-point data types. Lattice filters are used in a |
| variety of adaptive filter applications. The filter structure is feedforward and |
| the net impulse response is finite 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 FIRLattice.gif "Finite Impulse Response Lattice filter" |
| The following difference equation is implemented: |
| @par |
| <pre> |
| f0[n] = g0[n] = x[n] |
| fm[n] = fm-1[n] + km * gm-1[n-1] for m = 1, 2, ...M |
| gm[n] = km * fm-1[n] + gm-1[n-1] for m = 1, 2, ...M |
| y[n] = fM[n] |
| </pre> |
| @par |
| <code>pCoeffs</code> points to tha array of reflection coefficients of size <code>numStages</code>. |
| Reflection Coefficients are stored in the following order. |
| @par |
| <pre> |
| {k1, k2, ..., kM} |
| </pre> |
| where M is number of stages |
| @par |
| <code>pState</code> points to a state array of size <code>numStages</code>. |
| The state variables (g values) hold previous inputs and are stored in the following order. |
| <pre> |
| {g0[n], g1[n], g2[n] ...gM-1[n]} |
| </pre> |
| 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, pCoeffs, 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_fir_lattice_instance_f32 S = {numStages, pState, pCoeffs}; |
| arm_fir_lattice_instance_q31 S = {numStages, pState, pCoeffs}; |
| arm_fir_lattice_instance_q15 S = {numStages, pState, pCoeffs}; |
| </pre> |
| @par |
| where <code>numStages</code> is the number of stages in the filter; |
| <code>pState</code> is the address of the state buffer; |
| <code>pCoeffs</code> is the address of the coefficient buffer. |
| |
| @par Fixed-Point Behavior |
| Care must be taken when using the fixed-point versions of the FIR 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 FIR_Lattice |
| @{ |
| */ |
| |
| /** |
| @brief Processing function for the floating-point FIR lattice filter. |
| @param[in] S points to an instance of the floating-point FIR 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_fir_lattice_f32( |
| const arm_fir_lattice_instance_f32 * S, |
| const float32_t * pSrc, |
| float32_t * pDst, |
| uint32_t blockSize) |
| { |
| float32_t *pState = S->pState; /* State pointer */ |
| const float32_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ |
| float32_t *px; /* Temporary state pointer */ |
| const float32_t *pk; /* Temporary coefficient pointer */ |
| uint32_t numStages = S->numStages; /* Number of stages in the filter */ |
| uint32_t blkCnt, stageCnt; /* Loop counters */ |
| float32_t fcurr0, fnext0, gnext0, gcurr0; /* Temporary variables */ |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| float32_t fcurr1, fnext1, gnext1; /* Temporary variables for second sample in loop unrolling */ |
| float32_t fcurr2, fnext2, gnext2; /* Temporary variables for third sample in loop unrolling */ |
| float32_t fcurr3, fnext3, gnext3; /* Temporary variables for fourth sample in loop unrolling */ |
| #endif |
| |
| gcurr0 = 0.0f; |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| |
| /* Loop unrolling: Compute 4 outputs at a time */ |
| blkCnt = blockSize >> 2U; |
| |
| while (blkCnt > 0U) |
| { |
| /* Read two samples from input buffer */ |
| /* f0(n) = x(n) */ |
| fcurr0 = *pSrc++; |
| fcurr1 = *pSrc++; |
| |
| /* Initialize state pointer */ |
| px = pState; |
| |
| /* Initialize coeff pointer */ |
| pk = pCoeffs; |
| |
| /* Read g0(n-1) from state buffer */ |
| gcurr0 = *px; |
| |
| /* Process first sample for first tap */ |
| /* f1(n) = f0(n) + K1 * g0(n-1) */ |
| fnext0 = (gcurr0 * (*pk)) + fcurr0; |
| |
| /* g1(n) = f0(n) * K1 + g0(n-1) */ |
| gnext0 = (fcurr0 * (*pk)) + gcurr0; |
| |
| /* Process second sample for first tap */ |
| fnext1 = (fcurr0 * (*pk)) + fcurr1; |
| gnext1 = (fcurr1 * (*pk)) + fcurr0; |
| |
| /* Read next two samples from input buffer */ |
| /* f0(n+2) = x(n+2) */ |
| fcurr2 = *pSrc++; |
| fcurr3 = *pSrc++; |
| |
| /* Process third sample for first tap */ |
| fnext2 = (fcurr1 * (*pk)) + fcurr2; |
| gnext2 = (fcurr2 * (*pk)) + fcurr1; |
| |
| /* Process fourth sample for first tap */ |
| fnext3 = (fcurr2 * (*pk )) + fcurr3; |
| gnext3 = (fcurr3 * (*pk++)) + fcurr2; |
| |
| /* Copy only last input sample into the state buffer |
| which will be used for next samples processing */ |
| *px++ = fcurr3; |
| |
| /* Update of f values for next coefficient set processing */ |
| fcurr0 = fnext0; |
| fcurr1 = fnext1; |
| fcurr2 = fnext2; |
| fcurr3 = fnext3; |
| |
| /* Loop unrolling. Process 4 taps at a time . */ |
| stageCnt = (numStages - 1U) >> 2U; |
| |
| /* Loop over the number of taps. Unroll by a factor of 4. |
| Repeat until we've computed numStages-3 coefficients. */ |
| |
| /* Process 2nd, 3rd, 4th and 5th taps ... here */ |
| while (stageCnt > 0U) |
| { |
| /* Read g1(n-1), g3(n-1) .... from state */ |
| gcurr0 = *px; |
| |
| /* save g1(n) in state buffer */ |
| *px++ = gnext3; |
| |
| /* Process first sample for 2nd, 6th .. tap */ |
| /* Sample processing for K2, K6.... */ |
| /* f2(n) = f1(n) + K2 * g1(n-1) */ |
| fnext0 = (gcurr0 * (*pk)) + fcurr0; |
| |
| /* Process second sample for 2nd, 6th .. tap */ |
| /* for sample 2 processing */ |
| fnext1 = (gnext0 * (*pk)) + fcurr1; |
| |
| /* Process third sample for 2nd, 6th .. tap */ |
| fnext2 = (gnext1 * (*pk)) + fcurr2; |
| |
| /* Process fourth sample for 2nd, 6th .. tap */ |
| fnext3 = (gnext2 * (*pk)) + fcurr3; |
| |
| /* g2(n) = f1(n) * K2 + g1(n-1) */ |
| /* Calculation of state values for next stage */ |
| gnext3 = (fcurr3 * (*pk)) + gnext2; |
| |
| gnext2 = (fcurr2 * (*pk)) + gnext1; |
| |
| gnext1 = (fcurr1 * (*pk)) + gnext0; |
| |
| gnext0 = (fcurr0 * (*pk++)) + gcurr0; |
| |
| |
| /* Read g2(n-1), g4(n-1) .... from state */ |
| gcurr0 = *px; |
| |
| /* save g2(n) in state buffer */ |
| *px++ = gnext3; |
| |
| /* Sample processing for K3, K7.... */ |
| /* Process first sample for 3rd, 7th .. tap */ |
| /* f3(n) = f2(n) + K3 * g2(n-1) */ |
| fcurr0 = (gcurr0 * (*pk)) + fnext0; |
| |
| /* Process second sample for 3rd, 7th .. tap */ |
| fcurr1 = (gnext0 * (*pk)) + fnext1; |
| |
| /* Process third sample for 3rd, 7th .. tap */ |
| fcurr2 = (gnext1 * (*pk)) + fnext2; |
| |
| /* Process fourth sample for 3rd, 7th .. tap */ |
| fcurr3 = (gnext2 * (*pk)) + fnext3; |
| |
| /* Calculation of state values for next stage */ |
| /* g3(n) = f2(n) * K3 + g2(n-1) */ |
| gnext3 = (fnext3 * (*pk)) + gnext2; |
| |
| gnext2 = (fnext2 * (*pk)) + gnext1; |
| |
| gnext1 = (fnext1 * (*pk)) + gnext0; |
| |
| gnext0 = (fnext0 * (*pk++)) + gcurr0; |
| |
| |
| /* Read g1(n-1), g3(n-1) .... from state */ |
| gcurr0 = *px; |
| |
| /* save g3(n) in state buffer */ |
| *px++ = gnext3; |
| |
| /* Sample processing for K4, K8.... */ |
| /* Process first sample for 4th, 8th .. tap */ |
| /* f4(n) = f3(n) + K4 * g3(n-1) */ |
| fnext0 = (gcurr0 * (*pk)) + fcurr0; |
| |
| /* Process second sample for 4th, 8th .. tap */ |
| /* for sample 2 processing */ |
| fnext1 = (gnext0 * (*pk)) + fcurr1; |
| |
| /* Process third sample for 4th, 8th .. tap */ |
| fnext2 = (gnext1 * (*pk)) + fcurr2; |
| |
| /* Process fourth sample for 4th, 8th .. tap */ |
| fnext3 = (gnext2 * (*pk)) + fcurr3; |
| |
| /* g4(n) = f3(n) * K4 + g3(n-1) */ |
| /* Calculation of state values for next stage */ |
| gnext3 = (fcurr3 * (*pk)) + gnext2; |
| |
| gnext2 = (fcurr2 * (*pk)) + gnext1; |
| |
| gnext1 = (fcurr1 * (*pk)) + gnext0; |
| |
| gnext0 = (fcurr0 * (*pk++)) + gcurr0; |
| |
| |
| /* Read g2(n-1), g4(n-1) .... from state */ |
| gcurr0 = *px; |
| |
| /* save g4(n) in state buffer */ |
| *px++ = gnext3; |
| |
| /* Sample processing for K5, K9.... */ |
| /* Process first sample for 5th, 9th .. tap */ |
| /* f5(n) = f4(n) + K5 * g4(n-1) */ |
| fcurr0 = (gcurr0 * (*pk)) + fnext0; |
| |
| /* Process second sample for 5th, 9th .. tap */ |
| fcurr1 = (gnext0 * (*pk)) + fnext1; |
| |
| /* Process third sample for 5th, 9th .. tap */ |
| fcurr2 = (gnext1 * (*pk)) + fnext2; |
| |
| /* Process fourth sample for 5th, 9th .. tap */ |
| fcurr3 = (gnext2 * (*pk)) + fnext3; |
| |
| /* Calculation of state values for next stage */ |
| /* g5(n) = f4(n) * K5 + g4(n-1) */ |
| gnext3 = (fnext3 * (*pk)) + gnext2; |
| |
| gnext2 = (fnext2 * (*pk)) + gnext1; |
| |
| gnext1 = (fnext1 * (*pk)) + gnext0; |
| |
| gnext0 = (fnext0 * (*pk++)) + gcurr0; |
| |
| stageCnt--; |
| } |
| |
| /* If the (filter length -1) is not a multiple of 4, compute the remaining filter taps */ |
| stageCnt = (numStages - 1U) % 0x4U; |
| |
| while (stageCnt > 0U) |
| { |
| gcurr0 = *px; |
| |
| /* save g value in state buffer */ |
| *px++ = gnext3; |
| |
| /* Process four samples for last three taps here */ |
| fnext0 = (gcurr0 * (*pk)) + fcurr0; |
| |
| fnext1 = (gnext0 * (*pk)) + fcurr1; |
| |
| fnext2 = (gnext1 * (*pk)) + fcurr2; |
| |
| fnext3 = (gnext2 * (*pk)) + fcurr3; |
| |
| /* g1(n) = f0(n) * K1 + g0(n-1) */ |
| gnext3 = (fcurr3 * (*pk)) + gnext2; |
| |
| gnext2 = (fcurr2 * (*pk)) + gnext1; |
| |
| gnext1 = (fcurr1 * (*pk)) + gnext0; |
| |
| gnext0 = (fcurr0 * (*pk++)) + gcurr0; |
| |
| /* Update of f values for next coefficient set processing */ |
| fcurr0 = fnext0; |
| fcurr1 = fnext1; |
| fcurr2 = fnext2; |
| fcurr3 = fnext3; |
| |
| stageCnt--; |
| } |
| |
| /* The results in the 4 accumulators, store in the destination buffer. */ |
| /* y(n) = fN(n) */ |
| *pDst++ = fcurr0; |
| *pDst++ = fcurr1; |
| *pDst++ = fcurr2; |
| *pDst++ = fcurr3; |
| |
| blkCnt--; |
| } |
| |
| /* Loop unrolling: Compute remaining outputs */ |
| blkCnt = blockSize % 0x4U; |
| |
| #else |
| |
| /* Initialize blkCnt with number of samples */ |
| blkCnt = blockSize; |
| |
| #endif /* #if defined (ARM_MATH_LOOPUNROLL) */ |
| |
| while (blkCnt > 0U) |
| { |
| /* f0(n) = x(n) */ |
| fcurr0 = *pSrc++; |
| |
| /* Initialize state pointer */ |
| px = pState; |
| |
| /* Initialize coeff pointer */ |
| pk = pCoeffs; |
| |
| /* read g2(n) from state buffer */ |
| gcurr0 = *px; |
| |
| /* for sample 1 processing */ |
| /* f1(n) = f0(n) + K1 * g0(n-1) */ |
| fnext0 = (gcurr0 * (*pk)) + fcurr0; |
| |
| /* g1(n) = f0(n) * K1 + g0(n-1) */ |
| gnext0 = (fcurr0 * (*pk++)) + gcurr0; |
| |
| /* save g1(n) in state buffer */ |
| *px++ = fcurr0; |
| |
| /* f1(n) is saved in fcurr0 for next stage processing */ |
| fcurr0 = fnext0; |
| |
| stageCnt = (numStages - 1U); |
| |
| /* stage loop */ |
| while (stageCnt > 0U) |
| { |
| /* read g2(n) from state buffer */ |
| gcurr0 = *px; |
| |
| /* save g1(n) in state buffer */ |
| *px++ = gnext0; |
| |
| /* Sample processing for K2, K3.... */ |
| /* f2(n) = f1(n) + K2 * g1(n-1) */ |
| fnext0 = (gcurr0 * (*pk)) + fcurr0; |
| |
| /* g2(n) = f1(n) * K2 + g1(n-1) */ |
| gnext0 = (fcurr0 * (*pk++)) + gcurr0; |
| |
| /* f1(n) is saved in fcurr0 for next stage processing */ |
| fcurr0 = fnext0; |
| |
| stageCnt--; |
| } |
| |
| /* y(n) = fN(n) */ |
| *pDst++ = fcurr0; |
| |
| blkCnt--; |
| } |
| |
| } |
| |
| /** |
| @} end of FIR_Lattice group |
| */ |
