/* ---------------------------------------------------------------------- * Project: CMSIS DSP Library * Title: arm_biquad_cascade_df1_q31.c * Description: Processing function for the Q31 Biquad cascade filter * * $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 */ /** * @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 for Cortex-M3 and Cortex-M4. */ void arm_biquad_cascade_df1_q31( const arm_biquad_casd_df1_inst_q31 * S, q31_t * pSrc, q31_t * pDst, uint32_t blockSize) { q63_t acc; /* accumulator */ uint32_t uShift = ((uint32_t) S->postShift + 1U); uint32_t lShift = 32U - uShift; /* Shift to be applied to the output */ 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 */ 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 sample, stage = S->numStages; /* loop counters */ #if defined (ARM_MATH_DSP) q31_t acc_l, acc_h; /* temporary output variables */ /* Run the below code for Cortex-M4 and Cortex-M3 */ 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 */ /* Calc lower part of acc */ acc_l = acc & 0xffffffff; /* Calc upper part of acc */ acc_h = (acc >> 32) & 0xffffffff; /* Apply shift for lower part of acc and upper part of acc */ Yn2 = (uint32_t) acc_l >> lShift | acc_h << uShift; /* 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 */ /* Calc lower part of acc */ acc_l = acc & 0xffffffff; /* Calc upper part of acc */ acc_h = (acc >> 32) & 0xffffffff; /* Apply shift for lower part of acc and upper part of acc */ Yn1 = (uint32_t) acc_l >> lShift | acc_h << uShift; /* 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 */ /* Calc lower part of acc */ acc_l = acc & 0xffffffff; /* Calc upper part of acc */ acc_h = (acc >> 32) & 0xffffffff; /* Apply shift for lower part of acc and upper part of acc */ Yn2 = (uint32_t) acc_l >> lShift | acc_h << uShift; /* 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 */ /* Calc lower part of acc */ acc_l = acc & 0xffffffff; /* Calc upper part of acc */ acc_h = (acc >> 32) & 0xffffffff; /* Apply shift for lower part of acc and upper part of acc */ Yn1 = (uint32_t) acc_l >> lShift | acc_h << uShift; /* 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 >> lShift; /* 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); #else /* Run the below code for Cortex-M0 */ 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]; /* The variables acc holds the output value that is computed: * acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ sample = blockSize; 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 >> lShift; /* 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); #endif /* #if defined (ARM_MATH_DSP) */ } /** * @} end of BiquadCascadeDF1 group */