pigweed / third_party / github / STMicroelectronics / cmsis_core / cb6d9400754e6c9050487dfa573949b61152ac99 / . / DSP / Source / FilteringFunctions / arm_fir_q31.c

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

* Project: CMSIS DSP Library | |

* Title: arm_fir_q31.c | |

* Description: Q31 FIR filter processing function | |

* | |

* $Date: 27. January 2017 | |

* $Revision: V.1.5.1 | |

* | |

* Target Processor: Cortex-M cores | |

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

/* | |

* Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved. | |

* | |

* SPDX-License-Identifier: Apache-2.0 | |

* | |

* Licensed under the Apache License, Version 2.0 (the License); you may | |

* not use this file except in compliance with the License. | |

* You may obtain a copy of the License at | |

* | |

* www.apache.org/licenses/LICENSE-2.0 | |

* | |

* Unless required by applicable law or agreed to in writing, software | |

* distributed under the License is distributed on an AS IS BASIS, WITHOUT | |

* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |

* See the License for the specific language governing permissions and | |

* limitations under the License. | |

*/ | |

#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 */ | |

#if defined (ARM_MATH_DSP) | |

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

q31_t x0, x1, x2; /* 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; /* Accumulators */ | |

uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */ | |

uint32_t i, tapCnt, blkCnt, tapCntN3; /* 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 / 3; | |

blockSize = blockSize - (3 * blkCnt); | |

tapCnt = numTaps / 3; | |

tapCntN3 = numTaps - (3 * tapCnt); | |

/* 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 three new input samples into the state buffer */ | |

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

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

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

/* Set all accumulators to zero */ | |

acc0 = 0; | |

acc1 = 0; | |

acc2 = 0; | |

/* Initialize state pointer */ | |

px = pState; | |

/* Initialize coefficient pointer */ | |

pb = pCoeffs; | |

/* Read the first two samples from the state buffer: | |

* x[n-numTaps], x[n-numTaps-1] */ | |

x0 = *(px++); | |

x1 = *(px++); | |

/* Loop unrolling. Process 3 taps at a time. */ | |

i = tapCnt; | |

while (i > 0U) | |

{ | |

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

c0 = *pb; | |

/* Read x[n-numTaps-2] sample */ | |

x2 = *(px++); | |

/* Perform the multiply-accumulates */ | |

acc0 += ((q63_t) x0 * c0); | |

acc1 += ((q63_t) x1 * c0); | |

acc2 += ((q63_t) x2 * c0); | |

/* Read the coefficient and state */ | |

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

x0 = *(px++); | |

/* Perform the multiply-accumulates */ | |

acc0 += ((q63_t) x1 * c0); | |

acc1 += ((q63_t) x2 * c0); | |

acc2 += ((q63_t) x0 * c0); | |

/* Read the coefficient and state */ | |

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

x1 = *(px++); | |

/* update coefficient pointer */ | |

pb += 3U; | |

/* Perform the multiply-accumulates */ | |

acc0 += ((q63_t) x2 * c0); | |

acc1 += ((q63_t) x0 * c0); | |

acc2 += ((q63_t) x1 * c0); | |

/* Decrement the loop counter */ | |

i--; | |

} | |

/* If the filter length is not a multiple of 3, compute the remaining filter taps */ | |

i = tapCntN3; | |

while (i > 0U) | |

{ | |

/* Read coefficients */ | |

c0 = *(pb++); | |

/* Fetch 1 state variable */ | |

x2 = *(px++); | |

/* Perform the multiply-accumulates */ | |

acc0 += ((q63_t) x0 * c0); | |

acc1 += ((q63_t) x1 * c0); | |

acc2 += ((q63_t) x2 * c0); | |

/* Reuse the present sample states for next sample */ | |

x0 = x1; | |

x1 = x2; | |

/* Decrement the loop counter */ | |

i--; | |

} | |

/* Advance the state pointer by 3 to process the next group of 3 samples */ | |

pState = pState + 3; | |

/* The results in the 3 accumulators are in 2.30 format. Convert to 1.31 | |

** Then store the 3 outputs in the destination buffer. */ | |

*pDst++ = (q31_t) (acc0 >> 31U); | |

*pDst++ = (q31_t) (acc1 >> 31U); | |

*pDst++ = (q31_t) (acc2 >> 31U); | |

/* Decrement the samples loop counter */ | |

blkCnt--; | |

} | |

/* If the blockSize is not a multiple of 3, compute any remaining output samples here. | |

** No loop unrolling is used. */ | |

while (blockSize > 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 */ | |

blockSize--; | |

} | |

/* 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 /* #if defined (ARM_MATH_DSP) */ | |

} | |

/** | |

* @} end of FIR group | |

*/ |