| /* ---------------------------------------------------------------------- |
| * Project: CMSIS DSP Library |
| * Title: arm_fir_fast_q15.c |
| * Description: Q15 Fast 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 the Q15 FIR filter (fast version). |
| @param[in] S points to an instance of the Q15 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 |
| This fast version uses a 32-bit accumulator with 2.30 format. |
| The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit. |
| Thus, if the accumulator result overflows it wraps around and distorts the result. |
| In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits. |
| The 2.30 accumulator is then truncated to 2.15 format and saturated to yield the 1.15 result. |
| |
| @remark |
| Refer to \ref arm_fir_q15() for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion. Both the slow and the fast versions use the same instance structure. |
| Use function \ref arm_fir_init_q15() to initialize the filter structure. |
| */ |
| |
| void arm_fir_fast_q15( |
| const arm_fir_instance_q15 * S, |
| const q15_t * pSrc, |
| q15_t * pDst, |
| uint32_t blockSize) |
| { |
| q15_t *pState = S->pState; /* State pointer */ |
| const q15_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ |
| q15_t *pStateCurnt; /* Points to the current sample of the state */ |
| q15_t *px; /* Temporary pointer for state buffer */ |
| const q15_t *pb; /* Temporary pointer for coefficient buffer */ |
| q31_t acc0; /* Accumulators */ |
| uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */ |
| uint32_t tapCnt, blkCnt; /* Loop counters */ |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| q31_t acc1, acc2, acc3; /* Accumulators */ |
| q31_t x0, x1, x2, c0; /* Temporary variables to hold state and coefficient values */ |
| #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 >> 2U; |
| |
| while (blkCnt > 0U) |
| { |
| /* Copy 4 new input samples into the state buffer. */ |
| *pStateCurnt++ = *pSrc++; |
| *pStateCurnt++ = *pSrc++; |
| *pStateCurnt++ = *pSrc++; |
| *pStateCurnt++ = *pSrc++; |
| |
| /* Set all accumulators to zero */ |
| acc0 = 0; |
| acc1 = 0; |
| acc2 = 0; |
| acc3 = 0; |
| |
| /* Typecast q15_t pointer to q31_t pointer for state reading in q31_t */ |
| px = pState; |
| |
| /* Typecast q15_t pointer to q31_t pointer for coefficient reading in q31_t */ |
| pb = pCoeffs; |
| |
| /* Read the first two samples from the state buffer: x[n-N], x[n-N-1] */ |
| x0 = read_q15x2_ia (&px); |
| |
| /* Read the third and forth samples from the state buffer: x[n-N-2], x[n-N-3] */ |
| x2 = read_q15x2_ia (&px); |
| |
| /* Loop over the number of taps. Unroll by a factor of 4. |
| Repeat until we've computed numTaps-(numTaps%4) coefficients. */ |
| tapCnt = numTaps >> 2U; |
| |
| while (tapCnt > 0U) |
| { |
| /* Read the first two coefficients using SIMD: b[N] and b[N-1] coefficients */ |
| c0 = read_q15x2_ia ((q15_t **) &pb); |
| |
| /* acc0 += b[N] * x[n-N] + b[N-1] * x[n-N-1] */ |
| acc0 = __SMLAD(x0, c0, acc0); |
| |
| /* acc2 += b[N] * x[n-N-2] + b[N-1] * x[n-N-3] */ |
| acc2 = __SMLAD(x2, c0, acc2); |
| |
| /* pack x[n-N-1] and x[n-N-2] */ |
| #ifndef ARM_MATH_BIG_ENDIAN |
| x1 = __PKHBT(x2, x0, 0); |
| #else |
| x1 = __PKHBT(x0, x2, 0); |
| #endif |
| |
| /* Read state x[n-N-4], x[n-N-5] */ |
| x0 = read_q15x2_ia (&px); |
| |
| /* acc1 += b[N] * x[n-N-1] + b[N-1] * x[n-N-2] */ |
| acc1 = __SMLADX(x1, c0, acc1); |
| |
| /* pack x[n-N-3] and x[n-N-4] */ |
| #ifndef ARM_MATH_BIG_ENDIAN |
| x1 = __PKHBT(x0, x2, 0); |
| #else |
| x1 = __PKHBT(x2, x0, 0); |
| #endif |
| |
| /* acc3 += b[N] * x[n-N-3] + b[N-1] * x[n-N-4] */ |
| acc3 = __SMLADX(x1, c0, acc3); |
| |
| /* Read coefficients b[N-2], b[N-3] */ |
| c0 = read_q15x2_ia ((q15_t **) &pb); |
| |
| /* acc0 += b[N-2] * x[n-N-2] + b[N-3] * x[n-N-3] */ |
| acc0 = __SMLAD(x2, c0, acc0); |
| |
| /* Read state x[n-N-6], x[n-N-7] with offset */ |
| x2 = read_q15x2_ia (&px); |
| |
| /* acc2 += b[N-2] * x[n-N-4] + b[N-3] * x[n-N-5] */ |
| acc2 = __SMLAD(x0, c0, acc2); |
| |
| /* acc1 += b[N-2] * x[n-N-3] + b[N-3] * x[n-N-4] */ |
| acc1 = __SMLADX(x1, c0, acc1); |
| |
| /* pack x[n-N-5] and x[n-N-6] */ |
| #ifndef ARM_MATH_BIG_ENDIAN |
| x1 = __PKHBT(x2, x0, 0); |
| #else |
| x1 = __PKHBT(x0, x2, 0); |
| #endif |
| |
| /* acc3 += b[N-2] * x[n-N-5] + b[N-3] * x[n-N-6] */ |
| acc3 = __SMLADX(x1, c0, acc3); |
| |
| /* Decrement tap count */ |
| tapCnt--; |
| } |
| |
| /* If the filter length is not a multiple of 4, compute the remaining filter taps. |
| This is always be 2 taps since the filter length is even. */ |
| if ((numTaps & 0x3U) != 0U) |
| { |
| /* Read last two coefficients */ |
| c0 = read_q15x2_ia ((q15_t **) &pb); |
| |
| /* Perform the multiply-accumulates */ |
| acc0 = __SMLAD(x0, c0, acc0); |
| acc2 = __SMLAD(x2, c0, acc2); |
| |
| /* pack state variables */ |
| #ifndef ARM_MATH_BIG_ENDIAN |
| x1 = __PKHBT(x2, x0, 0); |
| #else |
| x1 = __PKHBT(x0, x2, 0); |
| #endif |
| |
| /* Read last state variables */ |
| x0 = read_q15x2 (px); |
| |
| /* Perform the multiply-accumulates */ |
| acc1 = __SMLADX(x1, c0, acc1); |
| |
| /* pack state variables */ |
| #ifndef ARM_MATH_BIG_ENDIAN |
| x1 = __PKHBT(x0, x2, 0); |
| #else |
| x1 = __PKHBT(x2, x0, 0); |
| #endif |
| |
| /* Perform the multiply-accumulates */ |
| acc3 = __SMLADX(x1, c0, acc3); |
| } |
| |
| /* The results in the 4 accumulators are in 2.30 format. Convert to 1.15 with saturation. |
| Then store the 4 outputs in the destination buffer. */ |
| #ifndef ARM_MATH_BIG_ENDIAN |
| write_q15x2_ia (&pDst, __PKHBT(__SSAT((acc0 >> 15), 16), __SSAT((acc1 >> 15), 16), 16)); |
| write_q15x2_ia (&pDst, __PKHBT(__SSAT((acc2 >> 15), 16), __SSAT((acc3 >> 15), 16), 16)); |
| #else |
| write_q15x2_ia (&pDst, __PKHBT(__SSAT((acc1 >> 15), 16), __SSAT((acc0 >> 15), 16), 16)); |
| write_q15x2_ia (&pDst, __PKHBT(__SSAT((acc3 >> 15), 16), __SSAT((acc2 >> 15), 16), 16)); |
| #endif /* #ifndef ARM_MATH_BIG_ENDIAN */ |
| |
| /* Advance the state pointer by 4 to process the next group of 4 samples */ |
| pState = pState + 4U; |
| |
| /* Decrement loop counter */ |
| blkCnt--; |
| } |
| |
| /* Loop unrolling: Compute remaining output samples */ |
| blkCnt = blockSize % 0x4U; |
| |
| #else |
| |
| /* Initialize blkCnt with number of taps */ |
| blkCnt = blockSize; |
| |
| #endif /* #if defined (ARM_MATH_LOOPUNROLL) */ |
| |
| while (blkCnt > 0U) |
| { |
| /* Copy two samples into state buffer */ |
| *pStateCurnt++ = *pSrc++; |
| |
| /* Set the accumulator to zero */ |
| acc0 = 0; |
| |
| /* Use SIMD to hold states and coefficients */ |
| px = pState; |
| pb = pCoeffs; |
| |
| tapCnt = numTaps >> 1U; |
| |
| do |
| { |
| acc0 += (q31_t) *px++ * *pb++; |
| acc0 += (q31_t) *px++ * *pb++; |
| |
| tapCnt--; |
| } |
| while (tapCnt > 0U); |
| |
| /* The result is in 2.30 format. Convert to 1.15 with saturation. |
| Then store the output in the destination buffer. */ |
| *pDst++ = (q15_t) (__SSAT((acc0 >> 15), 16)); |
| |
| /* 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 |
| */ |
