| /* ---------------------------------------------------------------------- |
| * Project: CMSIS DSP Library |
| * Title: arm_fir_q31.c |
| * Description: Q31 FIR filter processing function |
| * |
| * $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 FIR |
| @{ |
| */ |
| |
| /** |
| @brief Processing function for Q31 FIR filter. |
| @param[in] S points to an instance of the Q31 FIR filter 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 log2(numTaps) bits. |
| After all multiply-accumulates are performed, the 2.62 accumulator is right shifted by 31 bits and saturated to 1.31 format to yield the final result. |
| |
| @remark |
| Refer to \ref arm_fir_fast_q31() for a faster but less precise implementation of this filter. |
| */ |
| |
| void arm_fir_q31( |
| const arm_fir_instance_q31 * S, |
| const q31_t * pSrc, |
| q31_t * pDst, |
| uint32_t blockSize) |
| { |
| q31_t *pState = S->pState; /* State pointer */ |
| const q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ |
| q31_t *pStateCurnt; /* Points to the current sample of the state */ |
| q31_t *px; /* Temporary pointer for state buffer */ |
| const q31_t *pb; /* Temporary pointer for coefficient buffer */ |
| q63_t acc0; /* Accumulator */ |
| uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */ |
| uint32_t i, tapCnt, blkCnt; /* Loop counters */ |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| q63_t acc1, acc2; /* Accumulators */ |
| q31_t x0, x1, x2; /* Temporary variables to hold state values */ |
| q31_t c0; /* Temporary variable to hold coefficient value */ |
| #endif |
| |
| /* S->pState points to state array which contains previous frame (numTaps - 1) samples */ |
| /* pStateCurnt points to the location where the new input data should be written */ |
| pStateCurnt = &(S->pState[(numTaps - 1U)]); |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| |
| /* Loop unrolling: Compute 4 output values simultaneously. |
| * The variables acc0 ... acc3 hold output values that are being computed: |
| * |
| * acc0 = b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0] |
| * acc1 = b[numTaps-1] * x[n-numTaps] + b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1] |
| * acc2 = b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] + b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2] |
| * acc3 = b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps] +...+ b[0] * x[3] |
| */ |
| |
| blkCnt = blockSize / 3; |
| |
| while (blkCnt > 0U) |
| { |
| /* Copy 3 new input samples into the state buffer. */ |
| *pStateCurnt++ = *pSrc++; |
| *pStateCurnt++ = *pSrc++; |
| *pStateCurnt++ = *pSrc++; |
| |
| /* Set all accumulators to zero */ |
| acc0 = 0; |
| acc1 = 0; |
| acc2 = 0; |
| |
| /* Initialize state pointer */ |
| px = pState; |
| |
| /* Initialize coefficient pointer */ |
| pb = pCoeffs; |
| |
| /* Read the first 2 samples from the state buffer: x[n-numTaps], x[n-numTaps-1] */ |
| x0 = *px++; |
| x1 = *px++; |
| |
| /* Loop unrolling: process 3 taps at a time. */ |
| tapCnt = numTaps / 3; |
| |
| while (tapCnt > 0U) |
| { |
| /* Read the b[numTaps] coefficient */ |
| c0 = *pb; |
| |
| /* Read x[n-numTaps-2] sample */ |
| x2 = *(px++); |
| |
| /* Perform the multiply-accumulates */ |
| acc0 += ((q63_t) x0 * c0); |
| acc1 += ((q63_t) x1 * c0); |
| acc2 += ((q63_t) x2 * c0); |
| |
| /* Read the coefficient and state */ |
| c0 = *(pb + 1U); |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulates */ |
| acc0 += ((q63_t) x1 * c0); |
| acc1 += ((q63_t) x2 * c0); |
| acc2 += ((q63_t) x0 * c0); |
| |
| /* Read the coefficient and state */ |
| c0 = *(pb + 2U); |
| x1 = *(px++); |
| |
| /* update coefficient pointer */ |
| pb += 3U; |
| |
| /* Perform the multiply-accumulates */ |
| acc0 += ((q63_t) x2 * c0); |
| acc1 += ((q63_t) x0 * c0); |
| acc2 += ((q63_t) x1 * c0); |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| /* Loop unrolling: Compute remaining outputs */ |
| tapCnt = numTaps % 0x3U; |
| |
| while (tapCnt > 0U) |
| { |
| /* Read coefficients */ |
| c0 = *(pb++); |
| |
| /* Fetch 1 state variable */ |
| x2 = *(px++); |
| |
| /* Perform the multiply-accumulates */ |
| acc0 += ((q63_t) x0 * c0); |
| acc1 += ((q63_t) x1 * c0); |
| acc2 += ((q63_t) x2 * c0); |
| |
| /* Reuse the present sample states for next sample */ |
| x0 = x1; |
| x1 = x2; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| /* Advance the state pointer by 3 to process the next group of 3 samples */ |
| pState = pState + 3; |
| |
| /* The result is in 2.30 format. Convert to 1.31 and store in destination buffer. */ |
| *pDst++ = (q31_t) (acc0 >> 31U); |
| *pDst++ = (q31_t) (acc1 >> 31U); |
| *pDst++ = (q31_t) (acc2 >> 31U); |
| |
| /* Decrement loop counter */ |
| blkCnt--; |
| } |
| |
| /* Loop unrolling: Compute remaining output samples */ |
| blkCnt = blockSize % 0x3U; |
| |
| #else |
| |
| /* Initialize blkCnt with number of taps */ |
| blkCnt = blockSize; |
| |
| #endif /* #if defined (ARM_MATH_LOOPUNROLL) */ |
| |
| while (blkCnt > 0U) |
| { |
| /* Copy one sample at a time into state buffer */ |
| *pStateCurnt++ = *pSrc++; |
| |
| /* Set the accumulator to zero */ |
| acc0 = 0; |
| |
| /* Initialize state pointer */ |
| px = pState; |
| |
| /* Initialize Coefficient pointer */ |
| pb = pCoeffs; |
| |
| i = numTaps; |
| |
| /* Perform the multiply-accumulates */ |
| do |
| { |
| /* acc = b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0] */ |
| acc0 += (q63_t) *px++ * *pb++; |
| |
| i--; |
| } while (i > 0U); |
| |
| /* Result is in 2.62 format. Convert to 1.31 and store in destination buffer. */ |
| *pDst++ = (q31_t) (acc0 >> 31U); |
| |
| /* Advance state pointer by 1 for the next sample */ |
| pState = pState + 1U; |
| |
| /* Decrement 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; |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| |
| /* Loop unrolling: Compute 4 taps at a time */ |
| tapCnt = (numTaps - 1U) >> 2U; |
| |
| /* Copy data */ |
| while (tapCnt > 0U) |
| { |
| *pStateCurnt++ = *pState++; |
| *pStateCurnt++ = *pState++; |
| *pStateCurnt++ = *pState++; |
| *pStateCurnt++ = *pState++; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| /* Calculate remaining number of copies */ |
| tapCnt = (numTaps - 1U) % 0x4U; |
| |
| #else |
| |
| /* Initialize tapCnt with number of taps */ |
| tapCnt = (numTaps - 1U); |
| |
| #endif /* #if defined (ARM_MATH_LOOPUNROLL) */ |
| |
| /* Copy remaining data */ |
| while (tapCnt > 0U) |
| { |
| *pStateCurnt++ = *pState++; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| } |
| |
| /** |
| @} end of FIR group |
| */ |