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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_q31.c
- *
- * Description: Q31 FIR filter processing function.
- *
- * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
- *
- * 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 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 per call.
- * @return none.
- *
- * @details
- * <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.
- * After all multiply-accumulates are performed, the 2.62 accumulator is right shifted by 31 bits and saturated to 1.31 format to yield the final result.
- *
- * \par
- * Refer to the function <code>arm_fir_fast_q31()</code> for a faster but less precise implementation of this filter for Cortex-M3 and Cortex-M4.
- */
-
- void arm_fir_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 */
-
-
- #ifndef ARM_MATH_CM0_FAMILY
-
- /* Run the below code for Cortex-M4 and Cortex-M3 */
-
- q31_t x0, x1, x2; /* 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 */
- q63_t acc0, acc1, acc2; /* Accumulators */
- uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */
- uint32_t i, tapCnt, blkCnt, tapCntN3; /* Loop counters */
-
- /* 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)]);
-
- /* 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 / 3;
- blockSize = blockSize - (3 * blkCnt);
-
- tapCnt = numTaps / 3;
- tapCntN3 = numTaps - (3 * tapCnt);
-
- /* 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 three new input samples into the state buffer */
- *pStateCurnt++ = *pSrc++;
- *pStateCurnt++ = *pSrc++;
- *pStateCurnt++ = *pSrc++;
-
- /* Set all accumulators to zero */
- acc0 = 0;
- acc1 = 0;
- acc2 = 0;
-
- /* Initialize state pointer */
- px = pState;
-
- /* Initialize coefficient pointer */
- pb = pCoeffs;
-
- /* Read the first two samples from the state buffer:
- * x[n-numTaps], x[n-numTaps-1] */
- x0 = *(px++);
- x1 = *(px++);
-
- /* Loop unrolling. Process 3 taps at a time. */
- i = tapCnt;
-
- while(i > 0u)
- {
- /* Read the b[numTaps] coefficient */
- c0 = *pb;
-
- /* Read x[n-numTaps-2] sample */
- x2 = *(px++);
-
- /* Perform the multiply-accumulates */
- acc0 += ((q63_t) x0 * c0);
- acc1 += ((q63_t) x1 * c0);
- acc2 += ((q63_t) x2 * c0);
-
- /* Read the coefficient and state */
- c0 = *(pb + 1u);
- x0 = *(px++);
-
- /* Perform the multiply-accumulates */
- acc0 += ((q63_t) x1 * c0);
- acc1 += ((q63_t) x2 * c0);
- acc2 += ((q63_t) x0 * c0);
-
- /* Read the coefficient and state */
- c0 = *(pb + 2u);
- x1 = *(px++);
-
- /* update coefficient pointer */
- pb += 3u;
-
- /* Perform the multiply-accumulates */
- acc0 += ((q63_t) x2 * c0);
- acc1 += ((q63_t) x0 * c0);
- acc2 += ((q63_t) x1 * c0);
-
- /* Decrement the loop counter */
- i--;
- }
-
- /* If the filter length is not a multiple of 3, compute the remaining filter taps */
-
- i = tapCntN3;
-
- while(i > 0u)
- {
- /* Read coefficients */
- c0 = *(pb++);
-
- /* Fetch 1 state variable */
- x2 = *(px++);
-
- /* Perform the multiply-accumulates */
- acc0 += ((q63_t) x0 * c0);
- acc1 += ((q63_t) x1 * c0);
- acc2 += ((q63_t) x2 * c0);
-
- /* Reuse the present sample states for next sample */
- x0 = x1;
- x1 = x2;
-
- /* Decrement the loop counter */
- i--;
- }
-
- /* Advance the state pointer by 3 to process the next group of 3 samples */
- pState = pState + 3;
-
- /* The results in the 3 accumulators are in 2.30 format. Convert to 1.31
- ** Then store the 3 outputs in the destination buffer. */
- *pDst++ = (q31_t) (acc0 >> 31u);
- *pDst++ = (q31_t) (acc1 >> 31u);
- *pDst++ = (q31_t) (acc2 >> 31u);
-
- /* Decrement the samples loop counter */
- blkCnt--;
- }
-
- /* If the blockSize is not a multiple of 3, compute any remaining output samples here.
- ** No loop unrolling is used. */
-
- while(blockSize > 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
- {
- acc0 += (q63_t) * (px++) * (*(pb++));
- i--;
- } while(i > 0u);
-
- /* The result is in 2.62 format. Convert to 1.31
- ** Then store the output in the destination buffer. */
- *pDst++ = (q31_t) (acc0 >> 31u);
-
- /* Advance state pointer by 1 for the next sample */
- pState = pState + 1;
-
- /* Decrement the samples loop counter */
- blockSize--;
- }
-
- /* 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;
-
- tapCnt = (numTaps - 1u) >> 2u;
-
- /* copy data */
- while(tapCnt > 0u)
- {
- *pStateCurnt++ = *pState++;
- *pStateCurnt++ = *pState++;
- *pStateCurnt++ = *pState++;
- *pStateCurnt++ = *pState++;
-
- /* Decrement the loop counter */
- tapCnt--;
- }
-
- /* Calculate remaining number of copies */
- tapCnt = (numTaps - 1u) % 0x4u;
-
- /* Copy the remaining q31_t data */
- while(tapCnt > 0u)
- {
- *pStateCurnt++ = *pState++;
-
- /* Decrement the loop counter */
- tapCnt--;
- }
-
- #else
-
- /* Run the below code for Cortex-M0 */
-
- q31_t *px; /* Temporary pointer for state */
- q31_t *pb; /* Temporary pointer for coefficient buffer */
- q63_t acc; /* Accumulator */
- uint32_t numTaps = S->numTaps; /* Length of the filter */
- uint32_t i, tapCnt, blkCnt; /* Loop counters */
-
- /* 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)]);
-
- /* Initialize blkCnt with blockSize */
- blkCnt = blockSize;
-
- while(blkCnt > 0u)
- {
- /* Copy one sample at a time into state buffer */
- *pStateCurnt++ = *pSrc++;
-
- /* Set the accumulator to zero */
- acc = 0;
-
- /* Initialize state pointer */
- px = pState;
-
- /* Initialize Coefficient pointer */
- pb = pCoeffs;
-
- i = numTaps;
-
- /* Perform the multiply-accumulates */
- do
- {
- /* acc = 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] */
- acc += (q63_t) * px++ * *pb++;
- i--;
- } while(i > 0u);
-
- /* The result is in 2.62 format. Convert to 1.31
- ** Then store the output in the destination buffer. */
- *pDst++ = (q31_t) (acc >> 31u);
-
- /* 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 starting 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;
-
- /* Copy numTaps number of values */
- tapCnt = numTaps - 1u;
-
- /* Copy the data */
- while(tapCnt > 0u)
- {
- *pStateCurnt++ = *pState++;
-
- /* Decrement the loop counter */
- tapCnt--;
- }
-
-
- #endif /* #ifndef ARM_MATH_CM0_FAMILY */
-
- }
-
- /**
- * @} end of FIR group
- */
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