pigweed / third_party / github / STMicroelectronics / cmsis_core / refs/heads/cm4 / . / DSP / Source / FilteringFunctions / arm_biquad_cascade_df1_q31.c

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

* Project: CMSIS DSP Library | |

* Title: arm_biquad_cascade_df1_q31.c | |

* Description: Processing function for the Q31 Biquad cascade filter | |

* | |

* $Date: 18. March 2019 | |

* $Revision: V1.6.0 | |

* | |

* Target Processor: Cortex-M cores | |

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

/* | |

* Copyright (C) 2010-2019 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 BiquadCascadeDF1 | |

@{ | |

*/ | |

/** | |

@brief Processing function for the Q31 Biquad cascade filter. | |

@param[in] S points to an instance of the Q31 Biquad cascade 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 | |

@return none | |

@par Scaling and Overflow Behavior | |

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 2 bits and lie in the range [-0.25 +0.25). | |

After all 5 multiply-accumulates are performed, the 2.62 accumulator is shifted by <code>postShift</code> bits and the result truncated to | |

1.31 format by discarding the low 32 bits. | |

@remark | |

Refer to \ref arm_biquad_cascade_df1_fast_q31() for a faster but less precise implementation of this filter. | |

*/ | |

void arm_biquad_cascade_df1_q31( | |

const arm_biquad_casd_df1_inst_q31 * S, | |

const q31_t * pSrc, | |

q31_t * pDst, | |

uint32_t blockSize) | |

{ | |

const q31_t *pIn = pSrc; /* Source pointer */ | |

q31_t *pOut = pDst; /* Destination pointer */ | |

q31_t *pState = S->pState; /* pState pointer */ | |

const q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ | |

q63_t acc; /* Accumulator */ | |

q31_t b0, b1, b2, a1, a2; /* Filter coefficients */ | |

q31_t Xn1, Xn2, Yn1, Yn2; /* Filter pState variables */ | |

q31_t Xn; /* Temporary input */ | |

uint32_t uShift = ((uint32_t) S->postShift + 1U); | |

uint32_t lShift = 32U - uShift; /* Shift to be applied to the output */ | |

uint32_t sample, stage = S->numStages; /* Loop counters */ | |

#if defined (ARM_MATH_LOOPUNROLL) | |

q31_t acc_l, acc_h; /* temporary output variables */ | |

#endif | |

do | |

{ | |

/* Reading the coefficients */ | |

b0 = *pCoeffs++; | |

b1 = *pCoeffs++; | |

b2 = *pCoeffs++; | |

a1 = *pCoeffs++; | |

a2 = *pCoeffs++; | |

/* Reading the pState values */ | |

Xn1 = pState[0]; | |

Xn2 = pState[1]; | |

Yn1 = pState[2]; | |

Yn2 = pState[3]; | |

#if defined (ARM_MATH_LOOPUNROLL) | |

/* Apply loop unrolling and compute 4 output values simultaneously. */ | |

/* Variable acc hold output values that are being computed: | |

* | |

* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] | |

*/ | |

/* Loop unrolling: Compute 4 outputs at a time */ | |

sample = blockSize >> 2U; | |

while (sample > 0U) | |

{ | |

/* Read the first input */ | |

Xn = *pIn++; | |

/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ | |

acc = ((q63_t) b0 * Xn) + ((q63_t) b1 * Xn1) + ((q63_t) b2 * Xn2) + ((q63_t) a1 * Yn1) + ((q63_t) a2 * Yn2); | |

/* The result is converted to 1.31 , Yn2 variable is reused */ | |

acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */ | |

acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */ | |

/* Apply shift for lower part of acc and upper part of acc */ | |

Yn2 = (uint32_t) acc_l >> lShift | acc_h << uShift; | |

/* Store output in destination buffer. */ | |

*pOut++ = Yn2; | |

/* Read the second input */ | |

Xn2 = *pIn++; | |

/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ | |

acc = ((q63_t) b0 * Xn2) + ((q63_t) b1 * Xn) + ((q63_t) b2 * Xn1) + ((q63_t) a1 * Yn2) + ((q63_t) a2 * Yn1); | |

/* The result is converted to 1.31, Yn1 variable is reused */ | |

acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */ | |

acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */ | |

/* Apply shift for lower part of acc and upper part of acc */ | |

Yn1 = (uint32_t) acc_l >> lShift | acc_h << uShift; | |

/* Store output in destination buffer. */ | |

*pOut++ = Yn1; | |

/* Read the third input */ | |

Xn1 = *pIn++; | |

/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ | |

acc = ((q63_t) b0 * Xn1) + ((q63_t) b1 * Xn2) + ((q63_t) b2 * Xn) + ((q63_t) a1 * Yn1) + ((q63_t) a2 * Yn2); | |

/* The result is converted to 1.31, Yn2 variable is reused */ | |

acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */ | |

acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */ | |

/* Apply shift for lower part of acc and upper part of acc */ | |

Yn2 = (uint32_t) acc_l >> lShift | acc_h << uShift; | |

/* Store output in destination buffer. */ | |

*pOut++ = Yn2; | |

/* Read the forth input */ | |

Xn = *pIn++; | |

/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ | |

acc = ((q63_t) b0 * Xn) + ((q63_t) b1 * Xn1) + ((q63_t) b2 * Xn2) + ((q63_t) a1 * Yn2) + ((q63_t) a2 * Yn1); | |

/* The result is converted to 1.31, Yn1 variable is reused */ | |

acc_l = (acc ) & 0xffffffff; /* Calc lower part of acc */ | |

acc_h = (acc >> 32) & 0xffffffff; /* Calc upper part of acc */ | |

/* Apply shift for lower part of acc and upper part of acc */ | |

Yn1 = (uint32_t) acc_l >> lShift | acc_h << uShift; | |

/* Store output in destination buffer. */ | |

*pOut++ = Yn1; | |

/* Every time after the output is computed state should be updated. */ | |

/* The states should be updated as: */ | |

/* Xn2 = Xn1 */ | |

/* Xn1 = Xn */ | |

/* Yn2 = Yn1 */ | |

/* Yn1 = acc */ | |

Xn2 = Xn1; | |

Xn1 = Xn; | |

/* decrement loop counter */ | |

sample--; | |

} | |

/* Loop unrolling: Compute remaining outputs */ | |

sample = blockSize & 0x3U; | |

#else | |

/* Initialize blkCnt with number of samples */ | |

sample = blockSize; | |

#endif /* #if defined (ARM_MATH_LOOPUNROLL) */ | |

while (sample > 0U) | |

{ | |

/* Read the input */ | |

Xn = *pIn++; | |

/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ | |

acc = ((q63_t) b0 * Xn) + ((q63_t) b1 * Xn1) + ((q63_t) b2 * Xn2) + ((q63_t) a1 * Yn1) + ((q63_t) a2 * Yn2); | |

/* The result is converted to 1.31 */ | |

acc = acc >> lShift; | |

/* Store output in destination buffer. */ | |

*pOut++ = (q31_t) acc; | |

/* Every time after the output is computed state should be updated. */ | |

/* The states should be updated as: */ | |

/* Xn2 = Xn1 */ | |

/* Xn1 = Xn */ | |

/* Yn2 = Yn1 */ | |

/* Yn1 = acc */ | |

Xn2 = Xn1; | |

Xn1 = Xn; | |

Yn2 = Yn1; | |

Yn1 = (q31_t) acc; | |

/* decrement loop counter */ | |

sample--; | |

} | |

/* Store the updated state variables back into the pState array */ | |

*pState++ = Xn1; | |

*pState++ = Xn2; | |

*pState++ = Yn1; | |

*pState++ = Yn2; | |

/* The first stage goes from the input buffer to the output buffer. */ | |

/* Subsequent numStages occur in-place in the output buffer */ | |

pIn = pDst; | |

/* Reset output pointer */ | |

pOut = pDst; | |

/* decrement loop counter */ | |

stage--; | |

} while (stage > 0U); | |

} | |

/** | |

@} end of BiquadCascadeDF1 group | |

*/ |