arm_fir_decimate_f32.c
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r41 | /* ---------------------------------------------------------------------- | ||
* Copyright (C) 2010 ARM Limited. All rights reserved. | ||||
* | ||||
* $Date: 15. July 2011 | ||||
* $Revision: V1.0.10 | ||||
* | ||||
* Project: CMSIS DSP Library | ||||
* Title: arm_fir_decimate_f32.c | ||||
* | ||||
* Description: FIR decimation for floating-point sequences. | ||||
* | ||||
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 | ||||
* | ||||
* Version 1.0.10 2011/7/15 | ||||
* Big Endian support added and Merged M0 and M3/M4 Source code. | ||||
* | ||||
* Version 1.0.3 2010/11/29 | ||||
* Re-organized the CMSIS folders and updated documentation. | ||||
* | ||||
* Version 1.0.2 2010/11/11 | ||||
* Documentation updated. | ||||
* | ||||
* Version 1.0.1 2010/10/05 | ||||
* Production release and review comments incorporated. | ||||
* | ||||
* Version 1.0.0 2010/09/20 | ||||
* Production release and review comments incorporated | ||||
* | ||||
* Version 0.0.7 2010/06/10 | ||||
* Misra-C changes done | ||||
* | ||||
* -------------------------------------------------------------------- */ | ||||
#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. | ||||
* | ||||
* \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 */ | ||||
#ifndef ARM_MATH_CM0 | ||||
/* 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; | ||||
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; | ||||
/* 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 */ | ||||
blkCnt--; | ||||
} | ||||
/* 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 /* #ifndef ARM_MATH_CM0 */ | ||||
} | ||||
/** | ||||
* @} end of FIR_decimate group | ||||
*/ | ||||