pigweed / third_party / github / STMicroelectronics / cmsis_core / refs/heads/cm4 / . / DSP / Source / FilteringFunctions / arm_iir_lattice_f32.c

/* ---------------------------------------------------------------------- | |

* 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 | |

*/ |