CMSIS DSP library
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Diff: cmsis_dsp/FilteringFunctions/arm_fir_fast_q15.c
- Revision:
- 1:fdd22bb7aa52
- Child:
- 2:da51fb522205
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/cmsis_dsp/FilteringFunctions/arm_fir_fast_q15.c Wed Nov 28 12:30:09 2012 +0000 @@ -0,0 +1,341 @@ +/* ---------------------------------------------------------------------- +* Copyright (C) 2010 ARM Limited. All rights reserved. +* +* $Date: 15. February 2012 +* $Revision: V1.1.0 +* +* Project: CMSIS DSP Library +* Title: arm_fir_fast_q15.c +* +* Description: Q15 Fast FIR filter processing function. +* +* Target Processor: Cortex-M4/Cortex-M3 +* +* Version 1.1.0 2012/02/15 +* Updated with more optimizations, bug fixes and minor API changes. +* +* 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 */ + q31_t acc0, acc1, acc2, acc3; /* Accumulators */ + q15_t *pb; /* Temporary pointer for coefficient buffer */ + q15_t *px; /* Temporary q31 pointer for SIMD state buffer accesses */ + q31_t x0, x1, x2, c0; /* Temporary variables to hold SIMD state and coefficient values */ + uint32_t numTaps = S->numTaps; /* Number of taps in the filter */ + uint32_t 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. + ** Use 32-bit SIMD to move the 16-bit data. Only requires two copies. */ + *pStateCurnt++ = *pSrc++; + *pStateCurnt++ = *pSrc++; + *pStateCurnt++ = *pSrc++; + *pStateCurnt++ = *pSrc++; + + + /* Set all accumulators to zero */ + acc0 = 0; + acc1 = 0; + acc2 = 0; + acc3 = 0; + + /* Typecast q15_t pointer to q31_t pointer for state reading in q31_t */ + px = pState; + + /* Typecast q15_t pointer to q31_t pointer for coefficient reading in q31_t */ + pb = pCoeffs; + + /* Read the first two samples from the state buffer: x[n-N], x[n-N-1] */ + x0 = *__SIMD32(px)++; + + /* Read the third and forth samples from the state buffer: x[n-N-2], x[n-N-3] */ + x2 = *__SIMD32(px)++; + + /* Loop over the number of taps. Unroll by a factor of 4. + ** Repeat until we've computed numTaps-(numTaps%4) coefficients. */ + tapCnt = numTaps >> 2; + + while(tapCnt > 0) + { + /* Read the first two coefficients using SIMD: b[N] and b[N-1] coefficients */ + c0 = *__SIMD32(pb)++; + + /* acc0 += b[N] * x[n-N] + b[N-1] * x[n-N-1] */ + acc0 = __SMLAD(x0, c0, acc0); + + /* acc2 += b[N] * x[n-N-2] + b[N-1] * x[n-N-3] */ + acc2 = __SMLAD(x2, c0, acc2); + + /* pack x[n-N-1] and x[n-N-2] */ +#ifndef ARM_MATH_BIG_ENDIAN + x1 = __PKHBT(x2, x0, 0); +#else + x1 = __PKHBT(x0, x2, 0); +#endif + + /* Read state x[n-N-4], x[n-N-5] */ + x0 = _SIMD32_OFFSET(px); + + /* acc1 += b[N] * x[n-N-1] + b[N-1] * x[n-N-2] */ + acc1 = __SMLADX(x1, c0, acc1); + + /* pack x[n-N-3] and x[n-N-4] */ +#ifndef ARM_MATH_BIG_ENDIAN + x1 = __PKHBT(x0, x2, 0); +#else + x1 = __PKHBT(x2, x0, 0); +#endif + + /* acc3 += b[N] * x[n-N-3] + b[N-1] * x[n-N-4] */ + acc3 = __SMLADX(x1, c0, acc3); + + /* Read coefficients b[N-2], b[N-3] */ + c0 = *__SIMD32(pb)++; + + /* acc0 += b[N-2] * x[n-N-2] + b[N-3] * x[n-N-3] */ + acc0 = __SMLAD(x2, c0, acc0); + + /* Read state x[n-N-6], x[n-N-7] with offset */ + x2 = _SIMD32_OFFSET(px + 2u); + + /* acc2 += b[N-2] * x[n-N-4] + b[N-3] * x[n-N-5] */ + acc2 = __SMLAD(x0, c0, acc2); + + /* acc1 += b[N-2] * x[n-N-3] + b[N-3] * x[n-N-4] */ + acc1 = __SMLADX(x1, c0, acc1); + + /* pack x[n-N-5] and x[n-N-6] */ +#ifndef ARM_MATH_BIG_ENDIAN + x1 = __PKHBT(x2, x0, 0); +#else + x1 = __PKHBT(x0, x2, 0); +#endif + + /* acc3 += b[N-2] * x[n-N-5] + b[N-3] * x[n-N-6] */ + acc3 = __SMLADX(x1, c0, acc3); + + /* Update state pointer for next state reading */ + px += 4u; + + /* Decrement tap count */ + tapCnt--; + + } + + /* If the filter length is not a multiple of 4, compute the remaining filter taps. + ** This is always be 2 taps since the filter length is even. */ + if((numTaps & 0x3u) != 0u) + { + + /* Read last two coefficients */ + c0 = *__SIMD32(pb)++; + + /* Perform the multiply-accumulates */ + acc0 = __SMLAD(x0, c0, acc0); + acc2 = __SMLAD(x2, c0, acc2); + + /* pack state variables */ +#ifndef ARM_MATH_BIG_ENDIAN + x1 = __PKHBT(x2, x0, 0); +#else + x1 = __PKHBT(x0, x2, 0); +#endif + + /* Read last state variables */ + x0 = *__SIMD32(px); + + /* Perform the multiply-accumulates */ + acc1 = __SMLADX(x1, c0, acc1); + + /* pack state variables */ +#ifndef ARM_MATH_BIG_ENDIAN + x1 = __PKHBT(x0, x2, 0); +#else + x1 = __PKHBT(x2, x0, 0); +#endif + + /* Perform the multiply-accumulates */ + acc3 = __SMLADX(x1, 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(__SSAT((acc0 >> 15), 16), __SSAT((acc1 >> 15), 16), 16); + + *__SIMD32(pDst)++ = + __PKHBT(__SSAT((acc2 >> 15), 16), __SSAT((acc3 >> 15), 16), 16); + +#else + + *__SIMD32(pDst)++ = + __PKHBT(__SSAT((acc1 >> 15), 16), __SSAT((acc0 >> 15), 16), 16); + + *__SIMD32(pDst)++ = + __PKHBT(__SSAT((acc3 >> 15), 16), __SSAT((acc2 >> 15), 16), 16); + + +#endif /* #ifndef ARM_MATH_BIG_ENDIAN */ + + /* Advance the state pointer by 4 to process the next group of 4 samples */ + pState = pState + 4u; + + /* 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 */ + px = pState; + pb = pCoeffs; + + tapCnt = numTaps >> 1u; + + do + { + + acc0 += (q31_t) * px++ * *pb++; + acc0 += (q31_t) * px++ * *pb++; + + 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) (__SSAT((acc0 >> 15), 16)); + + /* Advance state pointer by 1 for the next sample */ + pState = pState + 1u; + + /* 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) + { + *pStateCurnt++ = *pState++; + *pStateCurnt++ = *pState++; + *pStateCurnt++ = *pState++; + *pStateCurnt++ = *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 + */