/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date: 29. November 2010
* $Revision: V1.0.3
*
* Project: CMSIS DSP Library
* Title: arm_biquad_cascade_df1_q31.c
*
* Description: Processing function for the
* Q31 Biquad cascade filter
*
* Target Processor: Cortex-M4/Cortex-M3
*
* 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 0.0.5 2010/04/26
* incorporated review comments and updated with latest CMSIS layer
*
* Version 0.0.3 2010/03/10
* Initial version
* -------------------------------------------------------------------- */
#include "arm_math.h"
/**
* @ingroup groupFilters
*/
/**
* @addtogroup BiquadCascadeDF1
* @{
*/
/**
* @brief Processing function for the Q31 Biquad cascade filter.
* @param[in] *S points to an instance of the Q31 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.
*
* Scaling and Overflow Behavior:
* \par
* The function is implemented using an internal 64-bit accumulator.
* The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.
* Thus, if the accumulator result overflows it wraps around rather than clip.
* In order to avoid overflows completely the input signal must be scaled down by 2 bits and lie in the range [-0.25 +0.25).
* After all 5 multiply-accumulates are performed, the 2.62 accumulator is shifted by postShift bits and the result truncated to
* 1.31 format by discarding the low 32 bits.
*
* \par
* Refer to the function arm_biquad_cascade_df1_fast_q31() for a faster but less precise implementation of this filter.
*/
void arm_biquad_cascade_df1_q31(
const arm_biquad_casd_df1_inst_q31 * S,
q31_t * pSrc,
q31_t * pDst,
uint32_t blockSize)
{
q31_t *pIn = pSrc; /* input pointer initialization */
q31_t *pOut = pDst; /* output pointer initialization */
q31_t *pState = S->pState; /* pState pointer initialization */
q31_t *pCoeffs = S->pCoeffs; /* coeff pointer initialization */
q63_t acc; /* accumulator */
q31_t Xn1, Xn2, Yn1, Yn2; /* Filter state variables */
q31_t b0, b1, b2, a1, a2; /* Filter coefficients */
q31_t Xn; /* temporary input */
uint32_t shift = 32u - ((uint32_t) S->postShift + 1u); /* Shift to be applied to the output */
uint32_t sample, stage = S->numStages; /* loop counters */
do
{
/* Reading the coefficients */
b0 = *pCoeffs++;
b1 = *pCoeffs++;
b2 = *pCoeffs++;
a1 = *pCoeffs++;
a2 = *pCoeffs++;
/* Reading the state values */
Xn1 = pState[0];
Xn2 = pState[1];
Yn1 = pState[2];
Yn2 = pState[3];
/* Apply loop unrolling and compute 4 output values simultaneously. */
/* The variable acc hold output values that are being computed:
*
* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
*/
sample = blockSize >> 2u;
/* First part of the processing with loop unrolling. Compute 4 outputs at a time.
** a second loop below computes the remaining 1 to 3 samples. */
while(sample > 0u)
{
/* Read the input */
Xn = *pIn++;
/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
/* acc = b0 * x[n] */
acc = (q63_t) b0 *Xn;
/* acc += b1 * x[n-1] */
acc += (q63_t) b1 *Xn1;
/* acc += b[2] * x[n-2] */
acc += (q63_t) b2 *Xn2;
/* acc += a1 * y[n-1] */
acc += (q63_t) a1 *Yn1;
/* acc += a2 * y[n-2] */
acc += (q63_t) a2 *Yn2;
/* The result is converted to 1.31 , Yn2 variable is reused */
Yn2 = (q31_t) (acc >> shift);
/* Store the output in the destination buffer. */
*pOut++ = Yn2;
/* Read the second input */
Xn2 = *pIn++;
/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
/* acc = b0 * x[n] */
acc = (q63_t) b0 *Xn2;
/* acc += b1 * x[n-1] */
acc += (q63_t) b1 *Xn;
/* acc += b[2] * x[n-2] */
acc += (q63_t) b2 *Xn1;
/* acc += a1 * y[n-1] */
acc += (q63_t) a1 *Yn2;
/* acc += a2 * y[n-2] */
acc += (q63_t) a2 *Yn1;
/* The result is converted to 1.31, Yn1 variable is reused */
Yn1 = (q31_t) (acc >> shift);
/* Store the output in the destination buffer. */
*pOut++ = Yn1;
/* Read the third input */
Xn1 = *pIn++;
/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
/* acc = b0 * x[n] */
acc = (q63_t) b0 *Xn1;
/* acc += b1 * x[n-1] */
acc += (q63_t) b1 *Xn2;
/* acc += b[2] * x[n-2] */
acc += (q63_t) b2 *Xn;
/* acc += a1 * y[n-1] */
acc += (q63_t) a1 *Yn1;
/* acc += a2 * y[n-2] */
acc += (q63_t) a2 *Yn2;
/* The result is converted to 1.31, Yn2 variable is reused */
Yn2 = (q31_t) (acc >> shift);
/* Store the output in the destination buffer. */
*pOut++ = Yn2;
/* Read the forth input */
Xn = *pIn++;
/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
/* acc = b0 * x[n] */
acc = (q63_t) b0 *Xn;
/* acc += b1 * x[n-1] */
acc += (q63_t) b1 *Xn1;
/* acc += b[2] * x[n-2] */
acc += (q63_t) b2 *Xn2;
/* acc += a1 * y[n-1] */
acc += (q63_t) a1 *Yn2;
/* acc += a2 * y[n-2] */
acc += (q63_t) a2 *Yn1;
/* The result is converted to 1.31, Yn1 variable is reused */
Yn1 = (q31_t) (acc >> shift);
/* Every time after the output is computed state should be updated. */
/* The states should be updated as: */
/* Xn2 = Xn1 */
/* Xn1 = Xn */
/* Yn2 = Yn1 */
/* Yn1 = acc */
Xn2 = Xn1;
Xn1 = Xn;
/* Store the output in the destination buffer. */
*pOut++ = Yn1;
/* decrement the loop counter */
sample--;
}
/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
** No loop unrolling is used. */
sample = (blockSize & 0x3u);
while(sample > 0u)
{
/* Read the input */
Xn = *pIn++;
/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
/* acc = b0 * x[n] */
acc = (q63_t) b0 *Xn;
/* acc += b1 * x[n-1] */
acc += (q63_t) b1 *Xn1;
/* acc += b[2] * x[n-2] */
acc += (q63_t) b2 *Xn2;
/* acc += a1 * y[n-1] */
acc += (q63_t) a1 *Yn1;
/* acc += a2 * y[n-2] */
acc += (q63_t) a2 *Yn2;
/* The result is converted to 1.31 */
acc = acc >> shift;
/* Every time after the output is computed state should be updated. */
/* The states should be updated as: */
/* Xn2 = Xn1 */
/* Xn1 = Xn */
/* Yn2 = Yn1 */
/* Yn1 = acc */
Xn2 = Xn1;
Xn1 = Xn;
Yn2 = Yn1;
Yn1 = (q31_t) acc;
/* Store the output in the destination buffer. */
*pOut++ = (q31_t) acc;
/* decrement the loop counter */
sample--;
}
/* The first stage goes from the input buffer to the output buffer. */
/* Subsequent stages occur in-place in the output buffer */
pIn = pDst;
/* Reset to destination pointer */
pOut = pDst;
/* Store the updated state variables back into the pState array */
*pState++ = Xn1;
*pState++ = Xn2;
*pState++ = Yn1;
*pState++ = Yn2;
} while(--stage);
}
/**
* @} end of BiquadCascadeDF1 group
*/