| /* ---------------------------------------------------------------------- |
| * Project: CMSIS DSP Library |
| * Title: arm_biquad_cascade_df1_q31.c |
| * Description: Processing function for the Q31 Biquad cascade filter |
| * |
| * $Date: 18. March 2019 |
| * $Revision: V1.6.0 |
| * |
| * Target Processor: Cortex-M cores |
| * -------------------------------------------------------------------- */ |
| /* |
| * Copyright (C) 2010-2019 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 |
| @return none |
| |
| @par Scaling and Overflow Behavior |
| 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 <code>postShift</code> bits and the result truncated to |
| 1.31 format by discarding the low 32 bits. |
| @remark |
| Refer to \ref 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, |
| const q31_t * pSrc, |
| q31_t * pDst, |
| uint32_t blockSize) |
| { |
| const q31_t *pIn = pSrc; /* Source pointer */ |
| q31_t *pOut = pDst; /* Destination pointer */ |
| q31_t *pState = S->pState; /* pState pointer */ |
| const q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ |
| q63_t acc; /* Accumulator */ |
| q31_t b0, b1, b2, a1, a2; /* Filter coefficients */ |
| q31_t Xn1, Xn2, Yn1, Yn2; /* Filter pState variables */ |
| q31_t Xn; /* Temporary input */ |
| uint32_t uShift = ((uint32_t) S->postShift + 1U); |
| uint32_t lShift = 32U - uShift; /* Shift to be applied to the output */ |
| uint32_t sample, stage = S->numStages; /* Loop counters */ |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| q31_t acc_l, acc_h; /* temporary output variables */ |
| #endif |
| |
| do |
| { |
| /* Reading the coefficients */ |
| b0 = *pCoeffs++; |
| b1 = *pCoeffs++; |
| b2 = *pCoeffs++; |
| a1 = *pCoeffs++; |
| a2 = *pCoeffs++; |
| |
| /* Reading the pState values */ |
| Xn1 = pState[0]; |
| Xn2 = pState[1]; |
| Yn1 = pState[2]; |
| Yn2 = pState[3]; |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| |
| /* Apply loop unrolling and compute 4 output values simultaneously. */ |
| /* 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] |
| */ |
| |
| /* Loop unrolling: Compute 4 outputs at a time */ |
| sample = blockSize >> 2U; |
| |
| while (sample > 0U) |
| { |
| /* Read the first input */ |
| Xn = *pIn++; |
| |
| /* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ |
| acc = ((q63_t) b0 * Xn) + ((q63_t) b1 * Xn1) + ((q63_t) b2 * Xn2) + ((q63_t) a1 * Yn1) + ((q63_t) a2 * Yn2); |
| |
| /* The result is converted to 1.31 , Yn2 variable is reused */ |
| acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */ |
| acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */ |
| |
| /* Apply shift for lower part of acc and upper part of acc */ |
| Yn2 = (uint32_t) acc_l >> lShift | acc_h << uShift; |
| |
| /* Store output in 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 = ((q63_t) b0 * Xn2) + ((q63_t) b1 * Xn) + ((q63_t) b2 * Xn1) + ((q63_t) a1 * Yn2) + ((q63_t) a2 * Yn1); |
| |
| /* The result is converted to 1.31, Yn1 variable is reused */ |
| acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */ |
| acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */ |
| |
| /* Apply shift for lower part of acc and upper part of acc */ |
| Yn1 = (uint32_t) acc_l >> lShift | acc_h << uShift; |
| |
| /* Store output in 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 = ((q63_t) b0 * Xn1) + ((q63_t) b1 * Xn2) + ((q63_t) b2 * Xn) + ((q63_t) a1 * Yn1) + ((q63_t) a2 * Yn2); |
| |
| /* The result is converted to 1.31, Yn2 variable is reused */ |
| acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */ |
| acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */ |
| |
| /* Apply shift for lower part of acc and upper part of acc */ |
| Yn2 = (uint32_t) acc_l >> lShift | acc_h << uShift; |
| |
| /* Store output in 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 = ((q63_t) b0 * Xn) + ((q63_t) b1 * Xn1) + ((q63_t) b2 * Xn2) + ((q63_t) a1 * Yn2) + ((q63_t) a2 * Yn1); |
| |
| /* The result is converted to 1.31, Yn1 variable is reused */ |
| acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */ |
| acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */ |
| |
| /* Apply shift for lower part of acc and upper part of acc */ |
| Yn1 = (uint32_t) acc_l >> lShift | acc_h << uShift; |
| |
| /* Store output in destination buffer. */ |
| *pOut++ = Yn1; |
| |
| /* 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; |
| |
| /* decrement loop counter */ |
| sample--; |
| } |
| |
| /* Loop unrolling: Compute remaining outputs */ |
| sample = blockSize & 0x3U; |
| |
| #else |
| |
| /* Initialize blkCnt with number of samples */ |
| sample = blockSize; |
| |
| #endif /* #if defined (ARM_MATH_LOOPUNROLL) */ |
| |
| 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 = ((q63_t) b0 * Xn) + ((q63_t) b1 * Xn1) + ((q63_t) b2 * Xn2) + ((q63_t) a1 * Yn1) + ((q63_t) a2 * Yn2); |
| |
| /* The result is converted to 1.31 */ |
| acc = acc >> lShift; |
| |
| /* Store output in destination buffer. */ |
| *pOut++ = (q31_t) acc; |
| |
| /* 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; |
| |
| /* decrement loop counter */ |
| sample--; |
| } |
| |
| /* Store the updated state variables back into the pState array */ |
| *pState++ = Xn1; |
| *pState++ = Xn2; |
| *pState++ = Yn1; |
| *pState++ = Yn2; |
| |
| /* The first stage goes from the input buffer to the output buffer. */ |
| /* Subsequent numStages occur in-place in the output buffer */ |
| pIn = pDst; |
| |
| /* Reset output pointer */ |
| pOut = pDst; |
| |
| /* decrement loop counter */ |
| stage--; |
| |
| } while (stage > 0U); |
| |
| } |
| |
| /** |
| @} end of BiquadCascadeDF1 group |
| */ |