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- /* ----------------------------------------------------------------------
- * Copyright (C) 2010-2013 ARM Limited. All rights reserved.
- *
- * $Date: 17. January 2013
- * $Revision: V1.4.1
- *
- * 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++);
-
- /* Read x[n-numTaps-4] sample */
- x0 = *(px++);
-
- /* 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++);
-
- /* Read x[n-numTaps-5] sample */
- x1 = *(px++);
-
- /* 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++);
-
- /* Read x[n-numTaps-6] sample */
- x2 = *(px++);
-
- /* 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);
- 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
- */
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