| /* ---------------------------------------------------------------------- |
| * Copyright (C) 2010-2014 ARM Limited. All rights reserved. |
| * |
| * $Date: 19. March 2015 |
| * $Revision: V.1.4.5 |
| * |
| * Project: CMSIS DSP Library |
| * Title: arm_fir_decimate_fast_q31.c |
| * |
| * Description: Fast Q31 FIR Decimator. |
| * |
| * Target Processor: Cortex-M4/Cortex-M3 |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * - Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * - Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in |
| * the documentation and/or other materials provided with the |
| * distribution. |
| * - Neither the name of ARM LIMITED nor the names of its contributors |
| * may be used to endorse or promote products derived from this |
| * software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; |
| * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER |
| * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN |
| * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| * POSSIBILITY OF SUCH DAMAGE. |
| * -------------------------------------------------------------------- */ |
| |
| #include "arm_math.h" |
| |
| /** |
| * @ingroup groupFilters |
| */ |
| |
| /** |
| * @addtogroup FIR_decimate |
| * @{ |
| */ |
| |
| /** |
| * @brief Processing function for the Q31 FIR decimator (fast variant) for Cortex-M3 and Cortex-M4. |
| * @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 |
| * This function is optimized for speed at the expense of fixed-point precision and overflow protection. |
| * The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format. |
| * These intermediate results are added to a 2.30 accumulator. |
| * Finally, the accumulator is saturated and converted to a 1.31 result. |
| * The fast version has the same overflow behavior as the standard version and provides less precision since it discards the low 32 bits of each multiplication result. |
| * 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). |
| * |
| * \par |
| * Refer to the function <code>arm_fir_decimate_q31()</code> for a slower implementation of this function which uses a 64-bit accumulator to provide higher precision. |
| * Both the slow and the fast versions use the same instance structure. |
| * Use the function <code>arm_fir_decimate_init_q31()</code> to initialize the filter structure. |
| */ |
| |
| void arm_fir_decimate_fast_q31( |
| 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 */ |
| q31_t sum0; /* Accumulator */ |
| uint32_t numTaps = S->numTaps; /* Number of taps */ |
| uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */ |
| uint32_t blkCntN2; |
| q31_t x1; |
| q31_t acc0, acc1; |
| q31_t *px0, *px1; |
| |
| /* 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 / 2; |
| blkCntN2 = outBlockSize - (2 * blkCnt); |
| |
| while(blkCnt > 0u) |
| { |
| /* Copy decimation factor number of new input samples into the state buffer */ |
| i = 2 * S->M; |
| |
| do |
| { |
| *pStateCurnt++ = *pSrc++; |
| |
| } while(--i); |
| |
| /* Set accumulator to zero */ |
| acc0 = 0; |
| acc1 = 0; |
| |
| /* Initialize state pointer */ |
| px0 = pState; |
| px1 = pState + S->M; |
| |
| /* 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] for sample 0 sample 1 */ |
| x0 = *(px0); |
| x1 = *(px1); |
| |
| /* Perform the multiply-accumulate */ |
| acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32); |
| acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32); |
| |
| /* Read the b[numTaps-2] coefficient */ |
| c0 = *(pb + 1u); |
| |
| /* Read x[n-numTaps-2] for sample 0 sample 1 */ |
| x0 = *(px0 + 1u); |
| x1 = *(px1 + 1u); |
| |
| /* Perform the multiply-accumulate */ |
| acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32); |
| acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32); |
| |
| /* Read the b[numTaps-3] coefficient */ |
| c0 = *(pb + 2u); |
| |
| /* Read x[n-numTaps-3] for sample 0 sample 1 */ |
| x0 = *(px0 + 2u); |
| x1 = *(px1 + 2u); |
| pb += 4u; |
| |
| /* Perform the multiply-accumulate */ |
| acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32); |
| acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32); |
| |
| /* Read the b[numTaps-4] coefficient */ |
| c0 = *(pb - 1u); |
| |
| /* Read x[n-numTaps-4] for sample 0 sample 1 */ |
| x0 = *(px0 + 3u); |
| x1 = *(px1 + 3u); |
| |
| |
| /* Perform the multiply-accumulate */ |
| acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32); |
| acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32); |
| |
| /* update state pointers */ |
| px0 += 4u; |
| px1 += 4u; |
| |
| /* 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 = *(px0++); |
| x1 = *(px1++); |
| |
| /* Perform the multiply-accumulate */ |
| acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32); |
| acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32); |
| |
| /* 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 * 2; |
| |
| /* The result is in the accumulator, store in the destination buffer. */ |
| *pDst++ = (q31_t) (acc0 << 1); |
| *pDst++ = (q31_t) (acc1 << 1); |
| |
| /* Decrement the loop counter */ |
| blkCnt--; |
| } |
| |
| while(blkCntN2 > 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 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32); |
| |
| /* Read the b[numTaps-2] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-2] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32); |
| |
| /* Read the b[numTaps-3] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-3] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32); |
| |
| /* Read the b[numTaps-4] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-4] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32); |
| |
| /* 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 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32); |
| |
| /* 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 << 1); |
| |
| /* Decrement the loop counter */ |
| blkCntN2--; |
| } |
| |
| /* 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--; |
| } |
| } |
| |
| /** |
| * @} end of FIR_decimate group |
| */ |
