pigweed / third_party / github / STMicroelectronics / cmsis_core / cb6d9400754e6c9050487dfa573949b61152ac99 / . / DSP / Source / FilteringFunctions / arm_fir_decimate_f32.c

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

* Project: CMSIS DSP Library | |

* Title: arm_fir_decimate_f32.c | |

* Description: FIR decimation for floating-point sequences | |

* | |

* $Date: 27. January 2017 | |

* $Revision: V.1.5.1 | |

* | |

* Target Processor: Cortex-M cores | |

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

/* | |

* Copyright (C) 2010-2017 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_decimate Finite Impulse Response (FIR) Decimator | |

* | |

* These functions combine an FIR filter together with a decimator. | |

* They are used in multirate systems for reducing the sample rate of a signal without introducing aliasing distortion. | |

* Conceptually, the functions are equivalent to the block diagram below: | |

* \image html FIRDecimator.gif "Components included in the FIR Decimator functions" | |

* When decimating by a factor of <code>M</code>, the signal should be prefiltered by a lowpass filter with a normalized | |

* cutoff frequency of <code>1/M</code> in order to prevent aliasing distortion. | |

* The user of the function is responsible for providing the filter coefficients. | |

* | |

* The FIR decimator functions provided in the CMSIS DSP Library combine the FIR filter and the decimator in an efficient manner. | |

* Instead of calculating all of the FIR filter outputs and discarding <code>M-1</code> out of every <code>M</code>, only the | |

* samples output by the decimator are computed. | |

* The functions operate on blocks of input and output data. | |

* <code>pSrc</code> points to an array of <code>blockSize</code> input values and | |

* <code>pDst</code> points to an array of <code>blockSize/M</code> output values. | |

* In order to have an integer number of output samples <code>blockSize</code> | |

* must always be a multiple of the decimation factor <code>M</code>. | |

* | |

* The library provides separate functions for Q15, Q31 and floating-point data types. | |

* | |

* \par Algorithm: | |

* The FIR portion of the algorithm uses the standard form filter: | |

* <pre> | |

* y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1] | |

* </pre> | |

* where, <code>b[n]</code> are the filter coefficients. | |

* \par | |

* The <code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>. | |

* Coefficients are stored in time reversed order. | |

* \par | |

* <pre> | |

* {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]} | |

* </pre> | |

* \par | |

* <code>pState</code> points to a state array of size <code>numTaps + blockSize - 1</code>. | |

* Samples in the state buffer are stored in the order: | |

* \par | |

* <pre> | |

* {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]} | |

* </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 array should be allocated separately. | |

* 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. | |

* - Checks to make sure that the size of the input is a multiple of the decimation factor. | |

* To do this manually without calling the init function, assign the follow subfields of the instance structure: | |

* numTaps, pCoeffs, M (decimation factor), 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. | |

* The code below statically initializes each of the 3 different data type filter instance structures | |

* <pre> | |

*arm_fir_decimate_instance_f32 S = {M, numTaps, pCoeffs, pState}; | |

*arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState}; | |

*arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState}; | |

* </pre> | |

* where <code>M</code> is the decimation factor; <code>numTaps</code> is the number of filter coefficients in the filter; | |

* <code>pCoeffs</code> is the address of the coefficient buffer; | |

* <code>pState</code> is the address of the state buffer. | |

* Be sure to set the values in the state buffer to zeros when doing static initialization. | |

* | |

* \par Fixed-Point Behavior | |

* Care must be taken when using the fixed-point versions of the FIR decimate 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_decimate | |

* @{ | |

*/ | |

/** | |

* @brief Processing function for the floating-point FIR decimator. | |

* @param[in] *S points to an instance of the floating-point FIR decimator 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 input samples to process per call. | |

* @return none. | |

*/ | |

void arm_fir_decimate_f32( | |

const arm_fir_decimate_instance_f32 * S, | |

float32_t * pSrc, | |

float32_t * pDst, | |

uint32_t blockSize) | |

{ | |

float32_t *pState = S->pState; /* State pointer */ | |

float32_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ | |

float32_t *pStateCurnt; /* Points to the current sample of the state */ | |

float32_t *px, *pb; /* Temporary pointers for state and coefficient buffers */ | |

float32_t sum0; /* Accumulator */ | |

float32_t x0, c0; /* Temporary variables to hold state and coefficient values */ | |

uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */ | |

uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */ | |

#if defined (ARM_MATH_DSP) | |

uint32_t blkCntN4; | |

float32_t *px0, *px1, *px2, *px3; | |

float32_t acc0, acc1, acc2, acc3; | |

float32_t x1, x2, x3; | |

/* Run the below code for Cortex-M4 and Cortex-M3 */ | |

/* S->pState buffer contains previous frame (numTaps - 1) samples */ | |

/* pStateCurnt points to the location where the new input data should be written */ | |

pStateCurnt = S->pState + (numTaps - 1U); | |

/* Total number of output samples to be computed */ | |

blkCnt = outBlockSize / 4; | |

blkCntN4 = outBlockSize - (4 * blkCnt); | |

while (blkCnt > 0U) | |

{ | |

/* Copy 4 * decimation factor number of new input samples into the state buffer */ | |

i = 4 * S->M; | |

do | |

{ | |

*pStateCurnt++ = *pSrc++; | |

} while (--i); | |

/* Set accumulators to zero */ | |

acc0 = 0.0f; | |

acc1 = 0.0f; | |

acc2 = 0.0f; | |

acc3 = 0.0f; | |

/* Initialize state pointer for all the samples */ | |

px0 = pState; | |

px1 = pState + S->M; | |

px2 = pState + 2 * S->M; | |

px3 = pState + 3 * S->M; | |

/* Initialize coeff pointer */ | |

pb = pCoeffs; | |

/* Loop unrolling. Process 4 taps at a time. */ | |

tapCnt = numTaps >> 2; | |

/* Loop over the number of taps. Unroll by a factor of 4. | |

** Repeat until we've computed numTaps-4 coefficients. */ | |

while (tapCnt > 0U) | |

{ | |

/* Read the b[numTaps-1] coefficient */ | |

c0 = *(pb++); | |

/* Read x[n-numTaps-1] sample for acc0 */ | |

x0 = *(px0++); | |

/* Read x[n-numTaps-1] sample for acc1 */ | |

x1 = *(px1++); | |

/* Read x[n-numTaps-1] sample for acc2 */ | |

x2 = *(px2++); | |

/* Read x[n-numTaps-1] sample for acc3 */ | |

x3 = *(px3++); | |

/* Perform the multiply-accumulate */ | |

acc0 += x0 * c0; | |

acc1 += x1 * c0; | |

acc2 += x2 * c0; | |

acc3 += x3 * c0; | |

/* Read the b[numTaps-2] coefficient */ | |

c0 = *(pb++); | |

/* Read x[n-numTaps-2] sample for acc0, acc1, acc2, acc3 */ | |

x0 = *(px0++); | |

x1 = *(px1++); | |

x2 = *(px2++); | |

x3 = *(px3++); | |

/* Perform the multiply-accumulate */ | |

acc0 += x0 * c0; | |

acc1 += x1 * c0; | |

acc2 += x2 * c0; | |

acc3 += x3 * c0; | |

/* Read the b[numTaps-3] coefficient */ | |

c0 = *(pb++); | |

/* Read x[n-numTaps-3] sample acc0, acc1, acc2, acc3 */ | |

x0 = *(px0++); | |

x1 = *(px1++); | |

x2 = *(px2++); | |

x3 = *(px3++); | |

/* Perform the multiply-accumulate */ | |

acc0 += x0 * c0; | |

acc1 += x1 * c0; | |

acc2 += x2 * c0; | |

acc3 += x3 * c0; | |

/* Read the b[numTaps-4] coefficient */ | |

c0 = *(pb++); | |

/* Read x[n-numTaps-4] sample acc0, acc1, acc2, acc3 */ | |

x0 = *(px0++); | |

x1 = *(px1++); | |

x2 = *(px2++); | |

x3 = *(px3++); | |

/* Perform the multiply-accumulate */ | |

acc0 += x0 * c0; | |

acc1 += x1 * c0; | |

acc2 += x2 * c0; | |

acc3 += x3 * c0; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

/* If the filter length is not a multiple of 4, compute the remaining filter taps */ | |

tapCnt = numTaps % 0x4U; | |

while (tapCnt > 0U) | |

{ | |

/* Read coefficients */ | |

c0 = *(pb++); | |

/* Fetch state variables for acc0, acc1, acc2, acc3 */ | |

x0 = *(px0++); | |

x1 = *(px1++); | |

x2 = *(px2++); | |

x3 = *(px3++); | |

/* Perform the multiply-accumulate */ | |

acc0 += x0 * c0; | |

acc1 += x1 * c0; | |

acc2 += x2 * c0; | |

acc3 += x3 * c0; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

/* Advance the state pointer by the decimation factor | |

* to process the next group of decimation factor number samples */ | |

pState = pState + 4 * S->M; | |

/* The result is in the accumulator, store in the destination buffer. */ | |

*pDst++ = acc0; | |

*pDst++ = acc1; | |

*pDst++ = acc2; | |

*pDst++ = acc3; | |

/* Decrement the loop counter */ | |

blkCnt--; | |

} | |

while (blkCntN4 > 0U) | |

{ | |

/* Copy decimation factor number of new input samples into the state buffer */ | |

i = S->M; | |

do | |

{ | |

*pStateCurnt++ = *pSrc++; | |

} while (--i); | |

/* Set accumulator to zero */ | |

sum0 = 0.0f; | |

/* Initialize state pointer */ | |

px = pState; | |

/* Initialize coeff pointer */ | |

pb = pCoeffs; | |

/* Loop unrolling. Process 4 taps at a time. */ | |

tapCnt = numTaps >> 2; | |

/* Loop over the number of taps. Unroll by a factor of 4. | |

** Repeat until we've computed numTaps-4 coefficients. */ | |

while (tapCnt > 0U) | |

{ | |

/* Read the b[numTaps-1] coefficient */ | |

c0 = *(pb++); | |

/* Read x[n-numTaps-1] sample */ | |

x0 = *(px++); | |

/* Perform the multiply-accumulate */ | |

sum0 += x0 * c0; | |

/* Read the b[numTaps-2] coefficient */ | |

c0 = *(pb++); | |

/* Read x[n-numTaps-2] sample */ | |

x0 = *(px++); | |

/* Perform the multiply-accumulate */ | |

sum0 += x0 * c0; | |

/* Read the b[numTaps-3] coefficient */ | |

c0 = *(pb++); | |

/* Read x[n-numTaps-3] sample */ | |

x0 = *(px++); | |

/* Perform the multiply-accumulate */ | |

sum0 += x0 * c0; | |

/* Read the b[numTaps-4] coefficient */ | |

c0 = *(pb++); | |

/* Read x[n-numTaps-4] sample */ | |

x0 = *(px++); | |

/* Perform the multiply-accumulate */ | |

sum0 += x0 * c0; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

/* If the filter length is not a multiple of 4, compute the remaining filter taps */ | |

tapCnt = numTaps % 0x4U; | |

while (tapCnt > 0U) | |

{ | |

/* Read coefficients */ | |

c0 = *(pb++); | |

/* Fetch 1 state variable */ | |

x0 = *(px++); | |

/* Perform the multiply-accumulate */ | |

sum0 += x0 * c0; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

/* 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++ = sum0; | |

/* Decrement the loop counter */ | |

blkCntN4--; | |

} | |

/* 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 */ | |

pStateCurnt = S->pState; | |

i = (numTaps - 1U) >> 2; | |

/* copy data */ | |

while (i > 0U) | |

{ | |

*pStateCurnt++ = *pState++; | |

*pStateCurnt++ = *pState++; | |

*pStateCurnt++ = *pState++; | |

*pStateCurnt++ = *pState++; | |

/* Decrement the loop counter */ | |

i--; | |

} | |

i = (numTaps - 1U) % 0x04U; | |

/* copy data */ | |

while (i > 0U) | |

{ | |

*pStateCurnt++ = *pState++; | |

/* Decrement the loop counter */ | |

i--; | |

} | |

#else | |

/* Run the below code for Cortex-M0 */ | |

/* S->pState buffer contains previous frame (numTaps - 1) samples */ | |

/* pStateCurnt points to the location where the new input data should be written */ | |

pStateCurnt = S->pState + (numTaps - 1U); | |

/* Total number of output samples to be computed */ | |

blkCnt = outBlockSize; | |

while (blkCnt > 0U) | |

{ | |

/* Copy decimation factor number of new input samples into the state buffer */ | |

i = S->M; | |

do | |

{ | |

*pStateCurnt++ = *pSrc++; | |

} while (--i); | |

/* Set accumulator to zero */ | |

sum0 = 0.0f; | |

/* Initialize state pointer */ | |

px = pState; | |

/* Initialize coeff pointer */ | |

pb = pCoeffs; | |

tapCnt = numTaps; | |

while (tapCnt > 0U) | |

{ | |

/* Read coefficients */ | |

c0 = *pb++; | |

/* Fetch 1 state variable */ | |

x0 = *px++; | |

/* Perform the multiply-accumulate */ | |

sum0 += x0 * c0; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

/* 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++ = sum0; | |

/* Decrement the loop counter */ | |

blkCnt--; | |

} | |

/* Processing is complete. | |

** Now copy the last numTaps - 1 samples to the start of the state buffer. | |

** This prepares the state buffer for the next function call. */ | |

/* Points to the start of the state buffer */ | |

pStateCurnt = S->pState; | |

/* Copy numTaps number of values */ | |

i = (numTaps - 1U); | |

/* copy data */ | |

while (i > 0U) | |

{ | |

*pStateCurnt++ = *pState++; | |

/* Decrement the loop counter */ | |

i--; | |

} | |

#endif /* #if defined (ARM_MATH_DSP) */ | |

} | |

/** | |

* @} end of FIR_decimate group | |

*/ |