| /* ---------------------------------------------------------------------- |
| * Project: CMSIS DSP Library |
| * Title: arm_iir_lattice_q31.c |
| * Description: Q31 IIR Lattice filter processing function |
| * |
| * $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 IIR_Lattice |
| @{ |
| */ |
| |
| /** |
| @brief Processing function for the Q31 IIR lattice filter. |
| @param[in] S points to an instance of the Q31 IIR lattice 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*log2(numStages) bits. |
| After all multiply-accumulates are performed, the 2.62 accumulator is saturated to 1.32 format and then truncated to 1.31 format. |
| */ |
| |
| void arm_iir_lattice_q31( |
| const arm_iir_lattice_instance_q31 * S, |
| const q31_t * pSrc, |
| q31_t * pDst, |
| uint32_t blockSize) |
| { |
| q31_t *pState = S->pState; /* State pointer */ |
| q31_t *pStateCur; /* State current pointer */ |
| q31_t fcurr, fnext = 0, gcurr = 0, gnext; /* Temporary variables for lattice stages */ |
| q63_t acc; /* Accumlator */ |
| q31_t *px1, *px2, *pk, *pv; /* Temporary pointers for state and coef */ |
| uint32_t numStages = S->numStages; /* Number of stages */ |
| uint32_t blkCnt, tapCnt; /* Temporary variables for counts */ |
| |
| |
| /* initialise loop count */ |
| blkCnt = blockSize; |
| |
| #if defined (ARM_MATH_DSP) |
| |
| /* Sample processing */ |
| while (blkCnt > 0U) |
| { |
| /* Read Sample from input buffer */ |
| /* fN(n) = x(n) */ |
| fcurr = *pSrc++; |
| |
| /* Initialize Ladder coeff pointer */ |
| pv = &S->pvCoeffs[0]; |
| |
| /* Initialize Reflection coeff pointer */ |
| pk = &S->pkCoeffs[0]; |
| |
| /* Initialize state read pointer */ |
| px1 = pState; |
| |
| /* Initialize state write pointer */ |
| px2 = pState; |
| |
| /* Set accumulator to zero */ |
| acc = 0; |
| |
| /* Process sample for first tap */ |
| gcurr = *px1++; |
| /* fN-1(n) = fN(n) - kN * gN-1(n-1) */ |
| fnext = __QSUB(fcurr, (q31_t) (((q63_t) gcurr * (*pk )) >> 31)); |
| |
| /* gN(n) = kN * fN-1(n) + gN-1(n-1) */ |
| gnext = __QADD(gcurr, (q31_t) (((q63_t) fnext * (*pk++)) >> 31)); |
| |
| /* write gN-1(n-1) into state for next sample processing */ |
| *px2++ = gnext; |
| |
| /* y(n) += gN(n) * vN */ |
| acc += ((q63_t) gnext * *pv++); |
| |
| /* Update f values for next coefficient processing */ |
| fcurr = fnext; |
| |
| |
| #if defined (ARM_MATH_LOOPUNROLL) |
| |
| /* Loop unrolling: Compute 4 taps at a time. */ |
| tapCnt = (numStages - 1U) >> 2U; |
| |
| while (tapCnt > 0U) |
| { |
| /* Process sample for 2nd, 6th ...taps */ |
| /* Read gN-2(n-1) from state buffer */ |
| gcurr = *px1++; |
| /* fN-2(n) = fN-1(n) - kN-1 * gN-2(n-1) */ |
| fnext = __QSUB(fcurr, (q31_t) (((q63_t) gcurr * (*pk )) >> 31)); |
| /* gN-1(n) = kN-1 * fN-2(n) + gN-2(n-1) */ |
| gnext = __QADD(gcurr, (q31_t) (((q63_t) fnext * (*pk++)) >> 31)); |
| /* y(n) += gN-1(n) * vN-1 */ |
| /* process for gN-5(n) * vN-5, gN-9(n) * vN-9 ... */ |
| acc += ((q63_t) gnext * *pv++); |
| /* write gN-1(n) into state for next sample processing */ |
| *px2++ = gnext; |
| |
| /* Process sample for 3nd, 7th ...taps */ |
| /* Read gN-3(n-1) from state buffer */ |
| gcurr = *px1++; |
| /* Process sample for 3rd, 7th .. taps */ |
| /* fN-3(n) = fN-2(n) - kN-2 * gN-3(n-1) */ |
| fcurr = __QSUB(fnext, (q31_t) (((q63_t) gcurr * (*pk )) >> 31)); |
| /* gN-2(n) = kN-2 * fN-3(n) + gN-3(n-1) */ |
| gnext = __QADD(gcurr, (q31_t) (((q63_t) fcurr * (*pk++)) >> 31)); |
| /* y(n) += gN-2(n) * vN-2 */ |
| /* process for gN-6(n) * vN-6, gN-10(n) * vN-10 ... */ |
| acc += ((q63_t) gnext * *pv++); |
| /* write gN-2(n) into state for next sample processing */ |
| *px2++ = gnext; |
| |
| /* Process sample for 4th, 8th ...taps */ |
| /* Read gN-4(n-1) from state buffer */ |
| gcurr = *px1++; |
| /* Process sample for 4th, 8th .. taps */ |
| /* fN-4(n) = fN-3(n) - kN-3 * gN-4(n-1) */ |
| fnext = __QSUB(fcurr, (q31_t) (((q63_t) gcurr * (*pk )) >> 31)); |
| /* gN-3(n) = kN-3 * fN-4(n) + gN-4(n-1) */ |
| gnext = __QADD(gcurr, (q31_t) (((q63_t) fnext * (*pk++)) >> 31)); |
| /* y(n) += gN-3(n) * vN-3 */ |
| /* process for gN-7(n) * vN-7, gN-11(n) * vN-11 ... */ |
| acc += ((q63_t) gnext * *pv++); |
| /* write gN-3(n) into state for next sample processing */ |
| *px2++ = gnext; |
| |
| /* Process sample for 5th, 9th ...taps */ |
| /* Read gN-5(n-1) from state buffer */ |
| gcurr = *px1++; |
| /* Process sample for 5th, 9th .. taps */ |
| /* fN-5(n) = fN-4(n) - kN-4 * gN-1(n-1) */ |
| fcurr = __QSUB(fnext, (q31_t) (((q63_t) gcurr * (*pk )) >> 31)); |
| /* gN-4(n) = kN-4 * fN-5(n) + gN-5(n-1) */ |
| gnext = __QADD(gcurr, (q31_t) (((q63_t) fcurr * (*pk++)) >> 31)); |
| /* y(n) += gN-4(n) * vN-4 */ |
| /* process for gN-8(n) * vN-8, gN-12(n) * vN-12 ... */ |
| acc += ((q63_t) gnext * *pv++); |
| |
| /* write gN-4(n) into state for next sample processing */ |
| *px2++ = gnext; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| fnext = fcurr; |
| |
| /* Loop unrolling: Compute remaining taps */ |
| tapCnt = (numStages - 1U) % 0x4U; |
| |
| #else |
| |
| /* Initialize blkCnt with number of samples */ |
| tapCnt = (numStages - 1U); |
| |
| #endif /* #if defined (ARM_MATH_LOOPUNROLL) */ |
| |
| while (tapCnt > 0U) |
| { |
| gcurr = *px1++; |
| /* Process sample for last taps */ |
| fnext = __QSUB(fcurr, (q31_t) (((q63_t) gcurr * (*pk )) >> 31)); |
| gnext = __QADD(gcurr, (q31_t) (((q63_t) fnext * (*pk++)) >> 31)); |
| |
| /* Output samples for last taps */ |
| acc += ((q63_t) gnext * *pv++); |
| *px2++ = gnext; |
| fcurr = fnext; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| /* y(n) += g0(n) * v0 */ |
| acc += ((q63_t) fnext * *pv++); |
| |
| *px2++ = fnext; |
| |
| /* write out into pDst */ |
| *pDst++ = (q31_t) (acc >> 31U); |
| |
| /* Advance the state pointer by 4 to process the next group of 4 samples */ |
| pState = pState + 1U; |
| |
| /* Decrement loop counter */ |
| blkCnt--; |
| } |
| |
| /* Processing is complete. Now copy last S->numStages samples to start of the buffer |
| for the preperation of next frame process */ |
| |
| /* Points to the start of the state buffer */ |
| pStateCur = &S->pState[0]; |
| pState = &S->pState[blockSize]; |
| |
| /* Copy data */ |
| #if defined (ARM_MATH_LOOPUNROLL) |
| |
| /* Loop unrolling: Compute 4 taps at a time. */ |
| tapCnt = numStages >> 2U; |
| |
| while (tapCnt > 0U) |
| { |
| *pStateCur++ = *pState++; |
| *pStateCur++ = *pState++; |
| *pStateCur++ = *pState++; |
| *pStateCur++ = *pState++; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| /* Loop unrolling: Compute remaining taps */ |
| tapCnt = numStages % 0x4U; |
| |
| #else |
| |
| /* Initialize blkCnt with number of samples */ |
| tapCnt = (numStages - 1U); |
| |
| #endif /* #if defined (ARM_MATH_LOOPUNROLL) */ |
| |
| while (tapCnt > 0U) |
| { |
| *pStateCur++ = *pState++; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| #else /* #if defined (ARM_MATH_DSP) */ |
| |
| /* Sample processing */ |
| while (blkCnt > 0U) |
| { |
| /* Read Sample from input buffer */ |
| /* fN(n) = x(n) */ |
| fcurr = *pSrc++; |
| |
| /* Initialize Ladder coeff pointer */ |
| pv = &S->pvCoeffs[0]; |
| |
| /* Initialize Reflection coeff pointer */ |
| pk = &S->pkCoeffs[0]; |
| |
| /* Initialize state read pointer */ |
| px1 = pState; |
| |
| /* Initialize state write pointer */ |
| px2 = pState; |
| |
| /* Set accumulator to zero */ |
| acc = 0; |
| |
| tapCnt = numStages; |
| |
| while (tapCnt > 0U) |
| { |
| gcurr = *px1++; |
| /* Process sample */ |
| /* fN-1(n) = fN(n) - kN * gN-1(n-1) */ |
| fnext = clip_q63_to_q31(((q63_t) fcurr - ((q31_t) (((q63_t) gcurr * (*pk )) >> 31)))); |
| |
| /* gN(n) = kN * fN-1(n) + gN-1(n-1) */ |
| gnext = clip_q63_to_q31(((q63_t) gcurr + ((q31_t) (((q63_t) fnext * (*pk++)) >> 31)))); |
| |
| /* Output samples */ |
| /* y(n) += gN(n) * vN */ |
| acc += ((q63_t) gnext * *pv++); |
| |
| /* write gN-1(n-1) into state for next sample processing */ |
| *px2++ = gnext; |
| |
| /* Update f values for next coefficient processing */ |
| fcurr = fnext; |
| |
| tapCnt--; |
| } |
| |
| /* y(n) += g0(n) * v0 */ |
| acc += ((q63_t) fnext * *pv++); |
| |
| *px2++ = fnext; |
| |
| /* write out into pDst */ |
| *pDst++ = (q31_t) (acc >> 31U); |
| |
| /* Advance the state pointer by 1 to process the next group of samples */ |
| pState = pState + 1U; |
| |
| /* Decrement loop counter */ |
| blkCnt--; |
| } |
| |
| /* Processing is complete. Now copy last S->numStages samples to start of the buffer |
| for the preperation of next frame process */ |
| |
| /* Points to the start of the state buffer */ |
| pStateCur = &S->pState[0]; |
| pState = &S->pState[blockSize]; |
| |
| tapCnt = numStages; |
| |
| /* Copy data */ |
| while (tapCnt > 0U) |
| { |
| *pStateCur++ = *pState++; |
| |
| /* Decrement loop counter */ |
| tapCnt--; |
| } |
| |
| #endif /* #if defined (ARM_MATH_DSP) */ |
| |
| } |
| |
| /** |
| @} end of IIR_Lattice group |
| */ |