| /* ---------------------------------------------------------------------- |
| * Copyright (C) 2010 ARM Limited. All rights reserved. |
| * |
| * $Date: 15. July 2011 |
| * $Revision: V1.0.10 |
| * |
| * Project: CMSIS DSP Library |
| * Title: arm_fir_q31.c |
| * |
| * Description: Q31 FIR filter processing function. |
| * |
| * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 |
| * |
| * Version 1.0.10 2011/7/15 |
| * Big Endian support added and Merged M0 and M3/M4 Source code. |
| * |
| * Version 1.0.3 2010/11/29 |
| * Re-organized the CMSIS folders and updated documentation. |
| * |
| * Version 1.0.2 2010/11/11 |
| * Documentation updated. |
| * |
| * Version 1.0.1 2010/10/05 |
| * Production release and review comments incorporated. |
| * |
| * Version 1.0.0 2010/09/20 |
| * Production release and review comments incorporated. |
| * |
| * Version 0.0.5 2010/04/26 |
| * incorporated review comments and updated with latest CMSIS layer |
| * |
| * Version 0.0.3 2010/03/10 |
| * Initial version |
| * -------------------------------------------------------------------- */ |
| |
| #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 |
| |
| /* Run the below code for Cortex-M4 and Cortex-M3 */ |
| |
| 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 */ |
| q63_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 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 >> 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] */ |
| acc0 += ((q63_t) x0 * c0); |
| |
| /* acc1 += b[numTaps] * x[n-numTaps-1] */ |
| acc1 += ((q63_t) x1 * c0); |
| |
| /* acc2 += b[numTaps] * x[n-numTaps-2] */ |
| acc2 += ((q63_t) x2 * c0); |
| |
| /* acc3 += b[numTaps] * x[n-numTaps-3] */ |
| acc3 += ((q63_t) x3 * c0); |
| |
| /* Read the b[numTaps-1] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-4] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulates */ |
| acc0 += ((q63_t) x1 * c0); |
| acc1 += ((q63_t) x2 * c0); |
| acc2 += ((q63_t) x3 * c0); |
| acc3 += ((q63_t) x0 * c0); |
| |
| /* Read the b[numTaps-2] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-5] sample */ |
| x1 = *(px++); |
| |
| /* Perform the multiply-accumulates */ |
| acc0 += ((q63_t) x2 * c0); |
| acc1 += ((q63_t) x3 * c0); |
| acc2 += ((q63_t) x0 * c0); |
| acc3 += ((q63_t) x1 * c0); |
| /* Read the b[numTaps-3] coefficients */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-6] sample */ |
| x2 = *(px++); |
| |
| /* Perform the multiply-accumulates */ |
| acc0 += ((q63_t) x3 * c0); |
| acc1 += ((q63_t) x0 * c0); |
| acc2 += ((q63_t) x1 * c0); |
| acc3 += ((q63_t) 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 */ |
| acc0 += ((q63_t) x0 * c0); |
| acc1 += ((q63_t) x1 * c0); |
| acc2 += ((q63_t) x2 * c0); |
| acc3 += ((q63_t) 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 2.62 format. Convert to 1.31 |
| ** Then store the 4 outputs in the destination buffer. */ |
| *pDst++ = (q31_t) (acc0 >> 31u); |
| *pDst++ = (q31_t) (acc1 >> 31u); |
| *pDst++ = (q31_t) (acc2 >> 31u); |
| *pDst++ = (q31_t) (acc3 >> 31u); |
| |
| /* 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 |
| { |
| 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 */ |
| 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; |
| |
| 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 */ |
| |
| } |
| |
| /** |
| * @} end of FIR group |
| */ |
