/* ---------------------------------------------------------------------- * Copyright (C) 2010-2013 ARM Limited. All rights reserved. * * $Date: 17. January 2013 * $Revision: V1.4.1 * * Project: CMSIS DSP Library * Title: arm_iir_lattice_q31.c * * Description: Q31 IIR lattice 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 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * -------------------------------------------------------------------- */ #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. * * @details * Scaling and Overflow Behavior: * \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 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, q31_t * pSrc, q31_t * pDst, uint32_t blockSize) { q31_t fcurr, fnext = 0, gcurr = 0, gnext; /* Temporary variables for lattice stages */ q63_t acc; /* Accumlator */ uint32_t blkCnt, tapCnt; /* Temporary variables for counts */ q31_t *px1, *px2, *pk, *pv; /* Temporary pointers for state and coef */ uint32_t numStages = S->numStages; /* number of stages */ q31_t *pState; /* State pointer */ q31_t *pStateCurnt; /* State current pointer */ blkCnt = blockSize; pState = &S->pState[0]; #ifndef ARM_MATH_CM0_FAMILY /* Run the below code for Cortex-M4 and Cortex-M3 */ /* Sample processing */ while(blkCnt > 0u) { /* Read Sample from input buffer */ /* fN(n) = x(n) */ fcurr = *pSrc++; /* Initialize state read pointer */ px1 = pState; /* Initialize state write pointer */ px2 = pState; /* Set accumulator to zero */ acc = 0; /* Initialize Ladder coeff pointer */ pv = &S->pvCoeffs[0]; /* Initialize Reflection coeff pointer */ pk = &S->pkCoeffs[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; /* Loop unrolling. Process 4 taps at a time. */ tapCnt = (numStages - 1u) >> 2; 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; tapCnt--; } fnext = fcurr; /* If the filter length is not a multiple of 4, compute the remaining filter taps */ tapCnt = (numStages - 1u) % 0x4u; 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; 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; 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 */ pStateCurnt = &S->pState[0]; pState = &S->pState[blockSize]; tapCnt = numStages >> 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 = (numStages) % 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 */ /* Sample processing */ while(blkCnt > 0u) { /* Read Sample from input buffer */ /* fN(n) = x(n) */ fcurr = *pSrc++; /* Initialize state read pointer */ px1 = pState; /* Initialize state write pointer */ px2 = pState; /* Set accumulator to zero */ acc = 0; /* Initialize Ladder coeff pointer */ pv = &S->pvCoeffs[0]; /* Initialize Reflection coeff pointer */ pk = &S->pkCoeffs[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; 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 */ pStateCurnt = &S->pState[0]; pState = &S->pState[blockSize]; tapCnt = numStages; /* Copy the remaining q31_t data */ while(tapCnt > 0u) { *pStateCurnt++ = *pState++; /* Decrement the loop counter */ tapCnt--; } #endif /* #ifndef ARM_MATH_CM0_FAMILY */ } /** * @} end of IIR_Lattice group */