arm_fir_q7.c
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r16 | /* ---------------------------------------------------------------------- | ||
* Copyright (C) 2010 ARM Limited. All rights reserved. | ||||
* | ||||
* $Date: 29. November 2010 | ||||
* $Revision: V1.0.3 | ||||
* | ||||
* Project: CMSIS DSP Library | ||||
* Title: arm_fir_q7.c | ||||
* | ||||
* Description: Q7 FIR filter processing function. | ||||
* | ||||
* Target Processor: Cortex-M4/Cortex-M3 | ||||
* | ||||
* 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 Q7 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 | ||||
* The function is implemented using a 32-bit internal accumulator. | ||||
* Both coefficients and state variables are represented in 1.7 format and multiplications yield a 2.14 result. | ||||
* The 2.14 intermediate results are accumulated in a 32-bit accumulator in 18.14 format. | ||||
* There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved. | ||||
* The accumulator is converted to 18.7 format by discarding the low 7 bits. | ||||
* Finally, the result is truncated to 1.7 format. | ||||
*/ | ||||
void arm_fir_q7( | ||||
const arm_fir_instance_q7 * S, | ||||
q7_t * pSrc, | ||||
q7_t * pDst, | ||||
uint32_t blockSize) | ||||
{ | ||||
uint32_t numTaps = S->numTaps; /* Number of taps in the filter */ | ||||
uint32_t i, blkCnt; /* Loop counters */ | ||||
q7_t *pState = S->pState; /* State pointer */ | ||||
q7_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ | ||||
q7_t *px, *pb; /* Temporary pointers to state and coeff */ | ||||
q31_t acc = 0; /* Accumlator */ | ||||
q31_t input1, input2; /* Temporary variables to store input */ | ||||
q15_t in1, in2; /* Temporary variables to store input */ | ||||
q7_t *pStateCurnt; /* Points to the current sample of the state */ | ||||
/* 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); | ||||
i = blockSize >> 2u; | ||||
/* Copy four new input samples into the state buffer. | ||||
** Use 32-bit SIMD to move the four 8-bit data. Only requires one copy for every four samples. */ | ||||
while(i > 0u) | ||||
{ | ||||
*__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++; | ||||
i--; | ||||
} | ||||
i = blockSize % 0x4u; | ||||
/* Copy remining samples into the state buffer. */ | ||||
while(i > 0u) | ||||
{ | ||||
*pStateCurnt++ = *pSrc++; | ||||
i--; | ||||
} | ||||
blkCnt = blockSize; | ||||
/* Perform filtering upto BlockSize - BlockSize%4 */ | ||||
while(blkCnt > 0u) | ||||
{ | ||||
/* Set accumulator to zero */ | ||||
acc = 0; | ||||
/* Initialize state pointer of type q7 */ | ||||
px = pState; | ||||
/* Initialize coeff pointer of type q7 */ | ||||
pb = pCoeffs; | ||||
i = numTaps >> 2u; | ||||
/* Loop over the number of taps. Unroll by a factor of 4. | ||||
** Repeat until we've computed numTaps-4 coefficients. */ | ||||
while(i > 0u) | ||||
{ | ||||
/* Reading two inputs of state buffer and packing */ | ||||
in1 = (q15_t) * px++; | ||||
in2 = (q15_t) * px++; | ||||
input1 = ((q31_t) in1 & 0x0000FFFF) | ((q31_t) in2 << 16); | ||||
/* Reading two inputs of coefficient buffer and packing */ | ||||
in1 = (q15_t) * pb++; | ||||
in2 = (q15_t) * pb++; | ||||
input2 = ((q31_t) in1 & 0x0000FFFF) | ((q31_t) in2 << 16); | ||||
/* Perform Multiply and accumlation of 2 packed inputs and coefficients using SMLALD and store the result in accumlator. */ | ||||
acc = __SMLAD(input1, input2, acc); | ||||
/* Reading two inputs of state buffer and packing */ | ||||
in1 = (q15_t) * px++; | ||||
in2 = (q15_t) * px++; | ||||
input1 = ((q31_t) in1 & 0x0000FFFF) | ((q31_t) in2 << 16); | ||||
/* Reading two inputs of coefficient buffer and packing */ | ||||
in1 = (q15_t) * pb++; | ||||
in2 = (q15_t) * pb++; | ||||
input2 = ((q31_t) in1 & 0x0000FFFF) | ((q31_t) in2 << 16); | ||||
/* Perform Multiply and accumlation of 2 packed inputs and coefficients using SMLALD and store the result in accumlator. */ | ||||
acc = __SMLAD(input1, input2, acc); | ||||
/* Decrement the tap loop counter */ | ||||
i--; | ||||
} | ||||
i = numTaps % 0x4u; | ||||
/* If the filter length is not a multiple of 4, compute the remaining filter taps */ | ||||
while(i > 0u) | ||||
{ | ||||
acc = __SMLAD(*px++, *pb++, acc); | ||||
i--; | ||||
} | ||||
/* Saturate output */ | ||||
acc = __SSAT((acc >> 7), 8); | ||||
/*Store filter output */ | ||||
*pDst++ = (q7_t) (acc); | ||||
/* Advance the state pointer by 1 to process 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 */ | ||||
i = (numTaps - 1u) >> 2u; | ||||
/* Copy four values using integer pointer */ | ||||
while(i > 0u) | ||||
{ | ||||
*__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; | ||||
i--; | ||||
} | ||||
/* Calculation of count for remaining q7_t data */ | ||||
i = (numTaps - 1u) % 0x4u; | ||||
/* Copy of remaining q7_t data */ | ||||
while(i > 0u) | ||||
{ | ||||
*pStateCurnt++ = *pState++; | ||||
i--; | ||||
} | ||||
} | ||||
/** | ||||
* @} end of FIR group | ||||
*/ | ||||