| /* ---------------------------------------------------------------------- |
| * 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_fast_q31.c |
| * |
| * Description: Processing function for the Q31 Fast FIR filter. |
| * |
| * 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 |
| * @{ |
| */ |
| |
| /** |
| * @param[in] *S points to an instance of the Q31 structure. |
| * @param[in] *pSrc points to the block of input data. |
| * @param[out] *pDst points to the block output data. |
| * @param[in] blockSize number of 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. |
| * |
| * \par |
| * Refer to the function <code>arm_fir_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_init_q31()</code> to initialize the filter structure. |
| */ |
| |
| IAR_ONLY_LOW_OPTIMIZATION_ENTER |
| void arm_fir_fast_q31( |
| const arm_fir_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, x1, x2, x3; /* Temporary variables to hold state */ |
| q31_t c0; /* Temporary variable to hold coefficient value */ |
| q31_t *px; /* Temporary pointer for state */ |
| q31_t *pb; /* Temporary pointer for coefficient buffer */ |
| q31_t acc0, acc1, acc2, acc3; /* Accumulators */ |
| uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */ |
| uint32_t i, tapCnt, blkCnt; /* Loop counters */ |
| |
| /* S->pState points to buffer 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)]); |
| |
| /* Apply loop unrolling and 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 >> 2; |
| |
| /* First part of the processing with loop unrolling. Compute 4 outputs at a time. |
| ** a second loop below computes the remaining 1 to 3 samples. */ |
| while(blkCnt > 0u) |
| { |
| /* Copy four 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; |
| |
| /* Initialize state pointer */ |
| px = pState; |
| |
| /* Initialize coefficient pointer */ |
| pb = pCoeffs; |
| |
| /* Read the first three samples from the state buffer: |
| * x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */ |
| x0 = *(px++); |
| x1 = *(px++); |
| x2 = *(px++); |
| |
| /* Loop unrolling. Process 4 taps at a time. */ |
| tapCnt = numTaps >> 2; |
| i = tapCnt; |
| |
| while(i > 0u) |
| { |
| /* Read the b[numTaps] coefficient */ |
| c0 = *pb; |
| |
| /* Read x[n-numTaps-3] sample */ |
| x3 = *px; |
| |
| /* acc0 += b[numTaps] * x[n-numTaps] */ |
| multAcc_32x32_keep32_R(acc0, x0, c0); |
| |
| /* acc1 += b[numTaps] * x[n-numTaps-1] */ |
| multAcc_32x32_keep32_R(acc1, x1, c0); |
| |
| /* acc2 += b[numTaps] * x[n-numTaps-2] */ |
| multAcc_32x32_keep32_R(acc2, x2, c0); |
| |
| /* acc3 += b[numTaps] * x[n-numTaps-3] */ |
| multAcc_32x32_keep32_R(acc3, x3, c0); |
| |
| /* Read the b[numTaps-1] coefficient */ |
| c0 = *(pb + 1u); |
| |
| /* Read x[n-numTaps-4] sample */ |
| x0 = *(px + 1u); |
| |
| /* Perform the multiply-accumulates */ |
| multAcc_32x32_keep32_R(acc0, x1, c0); |
| multAcc_32x32_keep32_R(acc1, x2, c0); |
| multAcc_32x32_keep32_R(acc2, x3, c0); |
| multAcc_32x32_keep32_R(acc3, x0, c0); |
| |
| /* Read the b[numTaps-2] coefficient */ |
| c0 = *(pb + 2u); |
| |
| /* Read x[n-numTaps-5] sample */ |
| x1 = *(px + 2u); |
| |
| /* Perform the multiply-accumulates */ |
| multAcc_32x32_keep32_R(acc0, x2, c0); |
| multAcc_32x32_keep32_R(acc1, x3, c0); |
| multAcc_32x32_keep32_R(acc2, x0, c0); |
| multAcc_32x32_keep32_R(acc3, x1, c0); |
| |
| /* Read the b[numTaps-3] coefficients */ |
| c0 = *(pb + 3u); |
| |
| /* Read x[n-numTaps-6] sample */ |
| x2 = *(px + 3u); |
| |
| /* Perform the multiply-accumulates */ |
| multAcc_32x32_keep32_R(acc0, x3, c0); |
| multAcc_32x32_keep32_R(acc1, x0, c0); |
| multAcc_32x32_keep32_R(acc2, x1, c0); |
| multAcc_32x32_keep32_R(acc3, x2, c0); |
| |
| /* update coefficient pointer */ |
| pb += 4u; |
| px += 4u; |
| |
| /* Decrement the loop counter */ |
| i--; |
| } |
| |
| /* If the filter length is not a multiple of 4, compute the remaining filter taps */ |
| |
| i = numTaps - (tapCnt * 4u); |
| while(i > 0u) |
| { |
| /* Read coefficients */ |
| c0 = *(pb++); |
| |
| /* Fetch 1 state variable */ |
| x3 = *(px++); |
| |
| /* Perform the multiply-accumulates */ |
| multAcc_32x32_keep32_R(acc0, x0, c0); |
| multAcc_32x32_keep32_R(acc1, x1, c0); |
| multAcc_32x32_keep32_R(acc2, x2, c0); |
| multAcc_32x32_keep32_R(acc3, x3, c0); |
| |
| /* Reuse the present sample states for next sample */ |
| x0 = x1; |
| x1 = x2; |
| x2 = x3; |
| |
| /* Decrement the loop counter */ |
| i--; |
| } |
| |
| /* Advance the state pointer by 4 to process the next group of 4 samples */ |
| pState = pState + 4; |
| |
| /* The results in the 4 accumulators are in 2.30 format. Convert to 1.31 |
| ** Then store the 4 outputs in the destination buffer. */ |
| *pDst++ = (q31_t) (acc0 << 1); |
| *pDst++ = (q31_t) (acc1 << 1); |
| *pDst++ = (q31_t) (acc2 << 1); |
| *pDst++ = (q31_t) (acc3 << 1); |
| |
| /* Decrement the samples loop counter */ |
| blkCnt--; |
| } |
| |
| |
| /* If the blockSize is not a multiple of 4, compute any remaining output samples here. |
| ** No loop unrolling is used. */ |
| blkCnt = blockSize % 4u; |
| |
| 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 |
| { |
| multAcc_32x32_keep32_R(acc0, (*px++), (*(pb++))); |
| i--; |
| } while(i > 0u); |
| |
| /* The result is in 2.30 format. Convert to 1.31 |
| ** Then store the output in the destination buffer. */ |
| *pDst++ = (q31_t) (acc0 << 1); |
| |
| /* Advance state pointer by 1 for the next sample */ |
| pState = pState + 1; |
| |
| /* Decrement the samples 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; |
| |
| /* Calculate remaining number of copies */ |
| tapCnt = (numTaps - 1u); |
| |
| /* Copy the remaining q31_t data */ |
| while(tapCnt > 0u) |
| { |
| *pStateCurnt++ = *pState++; |
| |
| /* Decrement the loop counter */ |
| tapCnt--; |
| } |
| |
| |
| } |
| IAR_ONLY_LOW_OPTIMIZATION_EXIT |
| /** |
| * @} end of FIR group |
| */ |
