| /* ---------------------------------------------------------------------- |
| * Copyright (C) 2010 ARM Limited. All rights reserved. |
| * |
| * $Date: 15. July 2011 |
| * $Revision: V1.0.10 |
| * |
| * Project: CMSIS DSP Library |
| * Title: arm_fir_fast_q15.c |
| * |
| * Description: Q15 Fast FIR filter processing function. |
| * |
| * Target Processor: Cortex-M4/Cortex-M3 |
| * |
| * 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 0.0.9 2010/08/16 |
| * Initial version |
| * |
| * -------------------------------------------------------------------- */ |
| |
| #include "arm_math.h" |
| |
| /** |
| * @ingroup groupFilters |
| */ |
| |
| /** |
| * @addtogroup FIR |
| * @{ |
| */ |
| |
| /** |
| * @param[in] *S points to an instance of the Q15 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. |
| * |
| * <b>Scaling and Overflow Behavior:</b> |
| * \par |
| * This fast version uses a 32-bit accumulator with 2.30 format. |
| * The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit. |
| * Thus, if the accumulator result overflows it wraps around and distorts the result. |
| * In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits. |
| * The 2.30 accumulator is then truncated to 2.15 format and saturated to yield the 1.15 result. |
| * |
| * \par |
| * Refer to the function <code>arm_fir_q15()</code> for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion. Both the slow and the fast versions use the same instance structure. |
| * Use the function <code>arm_fir_init_q15()</code> to initialize the filter structure. |
| */ |
| |
| void arm_fir_fast_q15( |
| const arm_fir_instance_q15 * S, |
| q15_t * pSrc, |
| q15_t * pDst, |
| uint32_t blockSize) |
| { |
| q15_t *pState = S->pState; /* State pointer */ |
| q15_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ |
| q15_t *pStateCurnt; /* Points to the current sample of the state */ |
| q15_t *px1; /* Temporary q15 pointer for state buffer */ |
| q31_t *pb; /* Temporary pointer for coefficient buffer */ |
| q31_t *px2; /* Temporary q31 pointer for SIMD state buffer accesses */ |
| q31_t x0, x1, x2, x3, c0; /* Temporary variables to hold SIMD state and coefficient values */ |
| q31_t acc0, acc1, acc2, acc3; /* Accumulators */ |
| uint32_t numTaps = S->numTaps; /* Number of taps in the filter */ |
| uint32_t 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. |
| ** Use 32-bit SIMD to move the 16-bit data. Only requires two copies. */ |
| *__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++; |
| *__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++; |
| |
| /* Set all accumulators to zero */ |
| acc0 = 0; |
| acc1 = 0; |
| acc2 = 0; |
| acc3 = 0; |
| |
| /* Initialize state pointer of type q15 */ |
| px1 = pState; |
| |
| /* Initialize coeff pointer of type q31 */ |
| pb = (q31_t *) (pCoeffs); |
| |
| /* Read the first two samples from the state buffer: x[n-N], x[n-N-1] */ |
| x0 = *(q31_t *) (px1++); |
| |
| /* Read the third and forth samples from the state buffer: x[n-N-1], x[n-N-2] */ |
| x1 = *(q31_t *) (px1++); |
| |
| /* Loop over the number of taps. Unroll by a factor of 4. |
| ** Repeat until we've computed numTaps-4 coefficients. */ |
| tapCnt = numTaps >> 2; |
| do |
| { |
| /* Read the first two coefficients using SIMD: b[N] and b[N-1] coefficients */ |
| c0 = *(pb++); |
| |
| /* acc0 += b[N] * x[n-N] + b[N-1] * x[n-N-1] */ |
| acc0 = __SMLAD(x0, c0, acc0); |
| |
| /* acc1 += b[N] * x[n-N-1] + b[N-1] * x[n-N-2] */ |
| acc1 = __SMLAD(x1, c0, acc1); |
| |
| /* Read state x[n-N-2], x[n-N-3] */ |
| x2 = *(q31_t *) (px1++); |
| |
| /* Read state x[n-N-3], x[n-N-4] */ |
| x3 = *(q31_t *) (px1++); |
| |
| /* acc2 += b[N] * x[n-N-2] + b[N-1] * x[n-N-3] */ |
| acc2 = __SMLAD(x2, c0, acc2); |
| |
| /* acc3 += b[N] * x[n-N-3] + b[N-1] * x[n-N-4] */ |
| acc3 = __SMLAD(x3, c0, acc3); |
| |
| /* Read coefficients b[N-2], b[N-3] */ |
| c0 = *(pb++); |
| |
| /* acc0 += b[N-2] * x[n-N-2] + b[N-3] * x[n-N-3] */ |
| acc0 = __SMLAD(x2, c0, acc0); |
| |
| /* acc1 += b[N-2] * x[n-N-3] + b[N-3] * x[n-N-4] */ |
| acc1 = __SMLAD(x3, c0, acc1); |
| |
| /* Read state x[n-N-4], x[n-N-5] */ |
| x0 = *(q31_t *) (px1++); |
| |
| /* Read state x[n-N-5], x[n-N-6] */ |
| x1 = *(q31_t *) (px1++); |
| |
| /* acc2 += b[N-2] * x[n-N-4] + b[N-3] * x[n-N-5] */ |
| acc2 = __SMLAD(x0, c0, acc2); |
| |
| /* acc3 += b[N-2] * x[n-N-5] + b[N-3] * x[n-N-6] */ |
| acc3 = __SMLAD(x1, c0, acc3); |
| tapCnt--; |
| |
| } |
| while(tapCnt > 0u); |
| |
| /* If the filter length is not a multiple of 4, compute the remaining filter taps. |
| ** This is always 2 taps since the filter length is always even. */ |
| if((numTaps & 0x3u) != 0u) |
| { |
| /* Read 2 coefficients */ |
| c0 = *(pb++); |
| /* Fetch 4 state variables */ |
| x2 = *(q31_t *) (px1++); |
| x3 = *(q31_t *) (px1++); |
| |
| /* Perform the multiply-accumulates */ |
| acc0 = __SMLAD(x0, c0, acc0); |
| acc1 = __SMLAD(x1, c0, acc1); |
| acc2 = __SMLAD(x2, c0, acc2); |
| acc3 = __SMLAD(x3, c0, acc3); |
| } |
| |
| /* The results in the 4 accumulators are in 2.30 format. Convert to 1.15 with saturation. |
| ** Then store the 4 outputs in the destination buffer. */ |
| |
| #ifndef ARM_MATH_BIG_ENDIAN |
| |
| *__SIMD32(pDst)++ = __PKHBT((acc0 >> 15), (acc1 >> 15), 16u); |
| *__SIMD32(pDst)++ = __PKHBT((acc2 >> 15), (acc3 >> 15), 16u); |
| |
| #else |
| |
| *__SIMD32(pDst)++ = __PKHBT((acc1 >> 15), (acc0 >> 15), 16u); |
| *__SIMD32(pDst)++ = __PKHBT((acc3 >> 15), (acc2 >> 15), 16u); |
| |
| #endif /* #ifndef ARM_MATH_BIG_ENDIAN */ |
| |
| /* Advance the state pointer by 4 to process the next group of 4 samples */ |
| pState = pState + 4; |
| |
| /* Decrement the 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 % 0x4u; |
| while(blkCnt > 0u) |
| { |
| /* Copy two samples into state buffer */ |
| *pStateCurnt++ = *pSrc++; |
| |
| /* Set the accumulator to zero */ |
| acc0 = 0; |
| |
| /* Use SIMD to hold states and coefficients */ |
| px2 = (q31_t *) pState; |
| pb = (q31_t *) (pCoeffs); |
| tapCnt = numTaps >> 1; |
| |
| do |
| { |
| acc0 = __SMLAD(*px2++, *(pb++), acc0); |
| tapCnt--; |
| } |
| while(tapCnt > 0u); |
| |
| /* The result is in 2.30 format. Convert to 1.15 with saturation. |
| ** Then store the output in the destination buffer. */ |
| *pDst++ = (q15_t) ((acc0 >> 15)); |
| |
| /* Advance state pointer by 1 for the next sample */ |
| pState = pState + 1; |
| |
| /* Decrement the 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; |
| /* Calculation of count for copying integer writes */ |
| tapCnt = (numTaps - 1u) >> 2; |
| |
| while(tapCnt > 0u) |
| { |
| *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; |
| *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; |
| |
| tapCnt--; |
| } |
| |
| /* Calculation of count for remaining q15_t data */ |
| tapCnt = (numTaps - 1u) % 0x4u; |
| |
| /* copy remaining data */ |
| while(tapCnt > 0u) |
| { |
| *pStateCurnt++ = *pState++; |
| |
| /* Decrement the loop counter */ |
| tapCnt--; |
| } |
| } |
| |
| /** |
| * @} end of FIR group |
| */ |
