| /* ---------------------------------------------------------------------- |
| * Project: CMSIS DSP Library |
| * Title: arm_fir_decimate_q31.c |
| * Description: Q31 FIR Decimator |
| * |
| * $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 FIR_decimate |
| * @{ |
| */ |
| |
| /** |
| * @brief Processing function for the Q31 FIR decimator. |
| * @param[in] *S points to an instance of the Q31 FIR decimator 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 input samples to process per call. |
| * @return none |
| * |
| * <b>Scaling and Overflow Behavior:</b> |
| * \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 log2(numTaps) bits (where log2 is read as log to the base 2). |
| * After all multiply-accumulates are performed, the 2.62 accumulator is truncated to 1.32 format and then saturated to 1.31 format. |
| * |
| * \par |
| * Refer to the function <code>arm_fir_decimate_fast_q31()</code> for a faster but less precise implementation of this function for Cortex-M3 and Cortex-M4. |
| */ |
| |
| void arm_fir_decimate_q31( |
| const arm_fir_decimate_instance_q31 * S, |
| q31_t * pSrc, |
| q31_t * pDst, |
| uint32_t blockSize) |
| { |
| q31_t *pState = S->pState; /* State pointer */ |
| q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ |
| q31_t *pStateCurnt; /* Points to the current sample of the state */ |
| q31_t x0, c0; /* Temporary variables to hold state and coefficient values */ |
| q31_t *px; /* Temporary pointers for state buffer */ |
| q31_t *pb; /* Temporary pointers for coefficient buffer */ |
| q63_t sum0; /* Accumulator */ |
| uint32_t numTaps = S->numTaps; /* Number of taps */ |
| uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */ |
| |
| |
| #if defined (ARM_MATH_DSP) |
| |
| /* Run the below code for Cortex-M4 and Cortex-M3 */ |
| |
| /* S->pState buffer contains previous frame (numTaps - 1) samples */ |
| /* pStateCurnt points to the location where the new input data should be written */ |
| pStateCurnt = S->pState + (numTaps - 1U); |
| |
| /* Total number of output samples to be computed */ |
| blkCnt = outBlockSize; |
| |
| while (blkCnt > 0U) |
| { |
| /* Copy decimation factor number of new input samples into the state buffer */ |
| i = S->M; |
| |
| do |
| { |
| *pStateCurnt++ = *pSrc++; |
| |
| } while (--i); |
| |
| /* Set accumulator to zero */ |
| sum0 = 0; |
| |
| /* Initialize state pointer */ |
| px = pState; |
| |
| /* Initialize coeff pointer */ |
| pb = pCoeffs; |
| |
| /* Loop unrolling. Process 4 taps at a time. */ |
| tapCnt = numTaps >> 2; |
| |
| /* Loop over the number of taps. Unroll by a factor of 4. |
| ** Repeat until we've computed numTaps-4 coefficients. */ |
| while (tapCnt > 0U) |
| { |
| /* Read the b[numTaps-1] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-1] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 += (q63_t) x0 *c0; |
| |
| /* Read the b[numTaps-2] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-2] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 += (q63_t) x0 *c0; |
| |
| /* Read the b[numTaps-3] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-3] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 += (q63_t) x0 *c0; |
| |
| /* Read the b[numTaps-4] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-4] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 += (q63_t) x0 *c0; |
| |
| /* Decrement the loop counter */ |
| tapCnt--; |
| } |
| |
| /* If the filter length is not a multiple of 4, compute the remaining filter taps */ |
| tapCnt = numTaps % 0x4U; |
| |
| while (tapCnt > 0U) |
| { |
| /* Read coefficients */ |
| c0 = *(pb++); |
| |
| /* Fetch 1 state variable */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 += (q63_t) x0 *c0; |
| |
| /* Decrement the loop counter */ |
| tapCnt--; |
| } |
| |
| /* Advance the state pointer by the decimation factor |
| * to process the next group of decimation factor number samples */ |
| pState = pState + S->M; |
| |
| /* The result is in the accumulator, store in the destination buffer. */ |
| *pDst++ = (q31_t) (sum0 >> 31); |
| |
| /* Decrement the loop counter */ |
| blkCnt--; |
| } |
| |
| /* Processing is complete. |
| ** Now copy the last numTaps - 1 samples to the satrt 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; |
| |
| i = (numTaps - 1U) >> 2U; |
| |
| /* copy data */ |
| while (i > 0U) |
| { |
| *pStateCurnt++ = *pState++; |
| *pStateCurnt++ = *pState++; |
| *pStateCurnt++ = *pState++; |
| *pStateCurnt++ = *pState++; |
| |
| /* Decrement the loop counter */ |
| i--; |
| } |
| |
| i = (numTaps - 1U) % 0x04U; |
| |
| /* copy data */ |
| while (i > 0U) |
| { |
| *pStateCurnt++ = *pState++; |
| |
| /* Decrement the loop counter */ |
| i--; |
| } |
| |
| #else |
| |
| /* Run the below code for Cortex-M0 */ |
| |
| /* S->pState buffer contains previous frame (numTaps - 1) samples */ |
| /* pStateCurnt points to the location where the new input data should be written */ |
| pStateCurnt = S->pState + (numTaps - 1U); |
| |
| /* Total number of output samples to be computed */ |
| blkCnt = outBlockSize; |
| |
| while (blkCnt > 0U) |
| { |
| /* Copy decimation factor number of new input samples into the state buffer */ |
| i = S->M; |
| |
| do |
| { |
| *pStateCurnt++ = *pSrc++; |
| |
| } while (--i); |
| |
| /* Set accumulator to zero */ |
| sum0 = 0; |
| |
| /* Initialize state pointer */ |
| px = pState; |
| |
| /* Initialize coeff pointer */ |
| pb = pCoeffs; |
| |
| tapCnt = numTaps; |
| |
| while (tapCnt > 0U) |
| { |
| /* Read coefficients */ |
| c0 = *pb++; |
| |
| /* Fetch 1 state variable */ |
| x0 = *px++; |
| |
| /* Perform the multiply-accumulate */ |
| sum0 += (q63_t) x0 *c0; |
| |
| /* Decrement the loop counter */ |
| tapCnt--; |
| } |
| |
| /* Advance the state pointer by the decimation factor |
| * to process the next group of decimation factor number samples */ |
| pState = pState + S->M; |
| |
| /* The result is in the accumulator, store in the destination buffer. */ |
| *pDst++ = (q31_t) (sum0 >> 31); |
| |
| /* Decrement the 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; |
| |
| i = numTaps - 1U; |
| |
| /* copy data */ |
| while (i > 0U) |
| { |
| *pStateCurnt++ = *pState++; |
| |
| /* Decrement the loop counter */ |
| i--; |
| } |
| |
| #endif /* #if defined (ARM_MATH_DSP) */ |
| |
| } |
| |
| /** |
| * @} end of FIR_decimate group |
| */ |