pigweed / third_party / github / STMicroelectronics / cmsis_core / 7dd288b23bf605a3a2fafa81a29d2c96a2fd83ce / . / DSP_Lib / Source / FilteringFunctions / arm_fir_q7.c

/* ---------------------------------------------------------------------- | |

* Copyright (C) 2010-2014 ARM Limited. All rights reserved. | |

* | |

* $Date: 19. March 2015 | |

* $Revision: V.1.4.5 | |

* | |

* Project: CMSIS DSP Library | |

* Title: arm_fir_q7.c | |

* | |

* Description: Q7 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 | |

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* -------------------------------------------------------------------- */ | |

#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) | |

{ | |

#ifndef ARM_MATH_CM0_FAMILY | |

/* Run the below code for Cortex-M4 and Cortex-M3 */ | |

q7_t *pState = S->pState; /* State pointer */ | |

q7_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ | |

q7_t *pStateCurnt; /* Points to the current sample of the state */ | |

q7_t x0, x1, x2, x3; /* Temporary variables to hold state */ | |

q7_t c0; /* Temporary variable to hold coefficient value */ | |

q7_t *px; /* Temporary pointer for state */ | |

q7_t *pb; /* Temporary pointer for coefficient buffer */ | |

q31_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 += ((q15_t) x0 * c0); | |

/* acc1 += b[numTaps] * x[n-numTaps-1] */ | |

acc1 += ((q15_t) x1 * c0); | |

/* acc2 += b[numTaps] * x[n-numTaps-2] */ | |

acc2 += ((q15_t) x2 * c0); | |

/* acc3 += b[numTaps] * x[n-numTaps-3] */ | |

acc3 += ((q15_t) x3 * c0); | |

/* Read the b[numTaps-1] coefficient */ | |

c0 = *(pb + 1u); | |

/* Read x[n-numTaps-4] sample */ | |

x0 = *(px + 1u); | |

/* Perform the multiply-accumulates */ | |

acc0 += ((q15_t) x1 * c0); | |

acc1 += ((q15_t) x2 * c0); | |

acc2 += ((q15_t) x3 * c0); | |

acc3 += ((q15_t) x0 * c0); | |

/* Read the b[numTaps-2] coefficient */ | |

c0 = *(pb + 2u); | |

/* Read x[n-numTaps-5] sample */ | |

x1 = *(px + 2u); | |

/* Perform the multiply-accumulates */ | |

acc0 += ((q15_t) x2 * c0); | |

acc1 += ((q15_t) x3 * c0); | |

acc2 += ((q15_t) x0 * c0); | |

acc3 += ((q15_t) x1 * c0); | |

/* Read the b[numTaps-3] coefficients */ | |

c0 = *(pb + 3u); | |

/* Read x[n-numTaps-6] sample */ | |

x2 = *(px + 3u); | |

/* Perform the multiply-accumulates */ | |

acc0 += ((q15_t) x3 * c0); | |

acc1 += ((q15_t) x0 * c0); | |

acc2 += ((q15_t) x1 * c0); | |

acc3 += ((q15_t) x2 * c0); | |

/* update coefficient pointer */ | |

pb += 4u; | |

px += 4u; | |

/* Decrement the loop counter */ | |

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 += ((q15_t) x0 * c0); | |

acc1 += ((q15_t) x1 * c0); | |

acc2 += ((q15_t) x2 * c0); | |

acc3 += ((q15_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. */ | |

acc0 = __SSAT((acc0 >> 7u), 8); | |

*pDst++ = acc0; | |

acc1 = __SSAT((acc1 >> 7u), 8); | |

*pDst++ = acc1; | |

acc2 = __SSAT((acc2 >> 7u), 8); | |

*pDst++ = acc2; | |

acc3 = __SSAT((acc3 >> 7u), 8); | |

*pDst++ = acc3; | |

/* 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 += (q15_t) * (px++) * (*(pb++)); | |

i--; | |

} while(i > 0u); | |

/* The result is in 2.14 format. Convert to 1.7 | |

** Then store the output in the destination buffer. */ | |

*pDst++ = __SSAT((acc0 >> 7u), 8); | |

/* 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 */ | |

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 */ | |

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); | |

/* Initialize blkCnt with blockSize */ | |

blkCnt = blockSize; | |

/* Perform filtering upto BlockSize - BlockSize%4 */ | |

while(blkCnt > 0u) | |

{ | |

/* Copy one sample at a time into state buffer */ | |

*pStateCurnt++ = *pSrc++; | |

/* Set accumulator to zero */ | |

acc = 0; | |

/* Initialize state pointer of type q7 */ | |

px = pState; | |

/* Initialize coeff pointer of type q7 */ | |

pb = pCoeffs; | |

i = numTaps; | |

while(i > 0u) | |

{ | |

/* 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 += (q15_t) * px++ * *pb++; | |

i--; | |

} | |

/* Store the 1.7 format filter output in destination buffer */ | |

*pDst++ = (q7_t) __SSAT((acc >> 7), 8); | |

/* 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; | |

/* Copy numTaps number of values */ | |

i = (numTaps - 1u); | |

/* Copy q7_t data */ | |

while(i > 0u) | |

{ | |

*pStateCurnt++ = *pState++; | |

i--; | |

} | |

#endif /* #ifndef ARM_MATH_CM0_FAMILY */ | |

} | |

/** | |

* @} end of FIR group | |

*/ |