/* ----------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date: 19. March 2015
* $Revision: V.1.4.5
*
* Project: CMSIS DSP Library
* Title: arm_biquad_cascade_df1_f32.c
*
* Description: Processing function for the
* floating-point Biquad cascade DirectFormI(DF1) filter.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Redistribution and use in source and binary forms, with or without
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* - Redistributions in binary form must reproduce the above copyright
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* - Neither the name of ARM LIMITED nor the names of its contributors
* may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* -------------------------------------------------------------------- */
#include "arm_math.h"
/**
* @ingroup groupFilters
*/
/**
* @defgroup BiquadCascadeDF1 Biquad Cascade IIR Filters Using Direct Form I Structure
*
* This set of functions implements arbitrary order recursive (IIR) filters.
* The filters are implemented as a cascade of second order Biquad sections.
* The functions support Q15, Q31 and floating-point data types.
* Fast version of Q15 and Q31 also supported on CortexM4 and Cortex-M3.
*
* 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> points to the array of input data and
* <code>pDst</code> points to the array of output data.
* Both arrays contain <code>blockSize</code> values.
*
* \par Algorithm
* Each Biquad stage implements a second order filter using the difference equation:
* <pre>
* y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
* </pre>
* A Direct Form I algorithm is used with 5 coefficients and 4 state variables per stage.
* \image html Biquad.gif "Single Biquad filter stage"
* Coefficients <code>b0, b1 and b2 </code> multiply the input signal <code>x[n]</code> and are referred to as the feedforward coefficients.
* Coefficients <code>a1</code> and <code>a2</code> multiply the output signal <code>y[n]</code> and are referred to as the feedback coefficients.
* Pay careful attention to the sign of the feedback coefficients.
* Some design tools use the difference equation
* <pre>
* y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] - a1 * y[n-1] - a2 * y[n-2]
* </pre>
* In this case the feedback coefficients <code>a1</code> and <code>a2</code> must be negated when used with the CMSIS DSP Library.
*
* \par
* Higher order filters are realized as a cascade of second order sections.
* <code>numStages</code> refers to the number of second order stages used.
* For example, an 8th order filter would be realized with <code>numStages=4</code> second order stages.
* \image html BiquadCascade.gif "8th order filter using a cascade of Biquad stages"
* A 9th order filter would be realized with <code>numStages=5</code> second order stages with the coefficients for one of the stages configured as a first order filter (<code>b2=0</code> and <code>a2=0</code>).
*
* \par
* The <code>pState</code> points to state variables array.
* Each Biquad stage has 4 state variables <code>x[n-1], x[n-2], y[n-1],</code> and <code>y[n-2]</code>.
* The state variables are arranged in the <code>pState</code> array as:
* <pre>
* {x[n-1], x[n-2], y[n-1], y[n-2]}
* </pre>
*
* \par
* The 4 state variables for stage 1 are first, then the 4 state variables for stage 2, and so on.
* The state array has a total length of <code>4*numStages</code> values.
* 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 Init Functions
* There is also an associated initialization function for each data type.
* The initialization function performs 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 before static initialization.
* The code below statically initializes each of the 3 different data type filter instance structures
* <pre>
* arm_biquad_casd_df1_inst_f32 S1 = {numStages, pState, pCoeffs};
* arm_biquad_casd_df1_inst_q15 S2 = {numStages, pState, pCoeffs, postShift};
* arm_biquad_casd_df1_inst_q31 S3 = {numStages, pState, pCoeffs, postShift};
* </pre>
* where <code>numStages</code> is the number of Biquad stages in the filter; <code>pState</code> is the address of the state buffer;
* <code>pCoeffs</code> is the address of the coefficient buffer; <code>postShift</code> shift to be applied.
*
* \par Fixed-Point Behavior
* Care must be taken when using the Q15 and Q31 versions of the Biquad Cascade filter functions.
* Following issues must be considered:
* - Scaling of coefficients
* - Filter gain
* - Overflow and saturation
*
* \par
* <b>Scaling of coefficients: </b>
* Filter coefficients are represented as fractional values and
* coefficients are restricted to lie in the range <code>[-1 +1)</code>.
* The fixed-point functions have an additional scaling parameter <code>postShift</code>
* which allow the filter coefficients to exceed the range <code>[+1 -1)</code>.
* At the output of the filter's accumulator is a shift register which shifts the result by <code>postShift</code> bits.
* \image html BiquadPostshift.gif "Fixed-point Biquad with shift by postShift bits after accumulator"
* This essentially scales the filter coefficients by <code>2^postShift</code>.
* For example, to realize the coefficients
* <pre>
* {1.5, -0.8, 1.2, 1.6, -0.9}
* </pre>
* set the pCoeffs array to:
* <pre>
* {0.75, -0.4, 0.6, 0.8, -0.45}
* </pre>
* and set <code>postShift=1</code>
*
* \par
* <b>Filter gain: </b>
* The frequency response of a Biquad filter is a function of its coefficients.
* It is possible for the gain through the filter to exceed 1.0 meaning that the filter increases the amplitude of certain frequencies.
* This means that an input signal with amplitude < 1.0 may result in an output > 1.0 and these are saturated or overflowed based on the implementation of the filter.
* To avoid this behavior the filter needs to be scaled down such that its peak gain < 1.0 or the input signal must be scaled down so that the combination of input and filter are never overflowed.
*
* \par
* <b>Overflow and saturation: </b>
* For Q15 and Q31 versions, it is described separately as part of the function specific documentation below.
*/
/**
* @addtogroup BiquadCascadeDF1
* @{
*/
/**
* @param[in] *S points to an instance of the floating-point Biquad cascade 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 per call.
* @return none.
*
*/
void arm_biquad_cascade_df1_f32(
const arm_biquad_casd_df1_inst_f32 * S,
float32_t * pSrc,
float32_t * pDst,
uint32_t blockSize)
{
float32_t *pIn = pSrc; /* source pointer */
float32_t *pOut = pDst; /* destination pointer */
float32_t *pState = S->pState; /* pState pointer */
float32_t *pCoeffs = S->pCoeffs; /* coeffic
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