pigweed / third_party / github / STMicroelectronics / cmsis_core / be0e91fb4ba19a2ee427ba8b6b75b43eb02b2810 / . / DSP / Source / FilteringFunctions / arm_correlate_fast_opt_q15.c

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

* Project: CMSIS DSP Library | |

* Title: arm_correlate_fast_opt_q15.c | |

* Description: Fast Q15 Correlation | |

* | |

* $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 Corr | |

@{ | |

*/ | |

/** | |

@brief Correlation of Q15 sequences (fast version). | |

@param[in] pSrcA points to the first input sequence | |

@param[in] srcALen length of the first input sequence | |

@param[in] pSrcB points to the second input sequence | |

@param[in] srcBLen length of the second input sequence. | |

@param[out] pDst points to the location where the output result is written. Length 2 * max(srcALen, srcBLen) - 1. | |

@param[in] pScratch points to scratch buffer of size max(srcALen, srcBLen) + 2*min(srcALen, srcBLen) - 2. | |

@return none | |

@par Scaling and Overflow Behavior | |

This fast version uses a 32-bit accumulator with 2.30 format. | |

The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit. | |

There is no saturation on intermediate additions. | |

Thus, if the accumulator overflows it wraps around and distorts the result. | |

The input signals should be scaled down to avoid intermediate overflows. | |

Scale down one of the inputs by 1/min(srcALen, srcBLen) to avoid overflow since a | |

maximum of min(srcALen, srcBLen) number of additions is carried internally. | |

The 2.30 accumulator is right shifted by 15 bits and then saturated to 1.15 format to yield the final result. | |

@remark | |

Refer to \ref arm_correlate_q15() for a slower implementation of this function which uses a 64-bit accumulator to avoid wrap around distortion. | |

*/ | |

void arm_correlate_fast_opt_q15( | |

const q15_t * pSrcA, | |

uint32_t srcALen, | |

const q15_t * pSrcB, | |

uint32_t srcBLen, | |

q15_t * pDst, | |

q15_t * pScratch) | |

{ | |

const q15_t *pIn1; /* InputA pointer */ | |

const q15_t *pIn2; /* InputB pointer */ | |

q31_t acc0; /* Accumulators */ | |

q15_t *pOut = pDst; /* Output pointer */ | |

q15_t *pScr1 = pScratch; /* Temporary pointer for scratch */ | |

const q15_t *py; /* Intermediate inputB pointer */ | |

uint32_t j, blkCnt, outBlockSize; /* Loop counter */ | |

int32_t inc = 1; /* Destination address modifier */ | |

uint32_t tapCnt; /* Loop count */ | |

#if defined (ARM_MATH_LOOPUNROLL) | |

q31_t acc1, acc2, acc3; /* Accumulators */ | |

q31_t x1, x2, x3; /* Temporary variables for holding input and coefficient values */ | |

q31_t y1, y2; /* State variables */ | |

#endif | |

/* The algorithm implementation is based on the lengths of the inputs. */ | |

/* srcB is always made to slide across srcA. */ | |

/* So srcBLen is always considered as shorter or equal to srcALen */ | |

/* But CORR(x, y) is reverse of CORR(y, x) */ | |

/* So, when srcBLen > srcALen, output pointer is made to point to the end of the output buffer */ | |

/* and the destination pointer modifier, inc is set to -1 */ | |

/* If srcALen > srcBLen, zero pad has to be done to srcB to make the two inputs of same length */ | |

/* But to improve the performance, | |

* we include zeroes in the output instead of zero padding either of the the inputs*/ | |

/* If srcALen > srcBLen, | |

* (srcALen - srcBLen) zeroes has to included in the starting of the output buffer */ | |

/* If srcALen < srcBLen, | |

* (srcALen - srcBLen) zeroes has to included in the ending of the output buffer */ | |

if (srcALen >= srcBLen) | |

{ | |

/* Initialization of inputA pointer */ | |

pIn1 = pSrcA; | |

/* Initialization of inputB pointer */ | |

pIn2 = pSrcB; | |

/* Number of output samples is calculated */ | |

outBlockSize = (2U * srcALen) - 1U; | |

/* When srcALen > srcBLen, zero padding is done to srcB | |

* to make their lengths equal. | |

* Instead, (outBlockSize - (srcALen + srcBLen - 1)) | |

* number of output samples are made zero */ | |

j = outBlockSize - (srcALen + (srcBLen - 1U)); | |

/* Updating the pointer position to non zero value */ | |

pOut += j; | |

} | |

else | |

{ | |

/* Initialization of inputA pointer */ | |

pIn1 = pSrcB; | |

/* Initialization of inputB pointer */ | |

pIn2 = pSrcA; | |

/* srcBLen is always considered as shorter or equal to srcALen */ | |

j = srcBLen; | |

srcBLen = srcALen; | |

srcALen = j; | |

/* CORR(x, y) = Reverse order(CORR(y, x)) */ | |

/* Hence set the destination pointer to point to the last output sample */ | |

pOut = pDst + ((srcALen + srcBLen) - 2U); | |

/* Destination address modifier is set to -1 */ | |

inc = -1; | |

} | |

pScr1 = pScratch; | |

/* Fill (srcBLen - 1U) zeros in scratch buffer */ | |

arm_fill_q15(0, pScr1, (srcBLen - 1U)); | |

/* Update temporary scratch pointer */ | |

pScr1 += (srcBLen - 1U); | |

/* Copy (srcALen) samples in scratch buffer */ | |

arm_copy_q15(pIn1, pScr1, srcALen); | |

/* Update pointers */ | |

pScr1 += srcALen; | |

/* Fill (srcBLen - 1U) zeros at end of scratch buffer */ | |

arm_fill_q15(0, pScr1, (srcBLen - 1U)); | |

/* Update pointer */ | |

pScr1 += (srcBLen - 1U); | |

/* Temporary pointer for scratch2 */ | |

py = pIn2; | |

/* Actual correlation process starts here */ | |

#if defined (ARM_MATH_LOOPUNROLL) | |

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

blkCnt = (srcALen + srcBLen - 1U) >> 2; | |

while (blkCnt > 0) | |

{ | |

/* Initialze temporary scratch pointer as scratch1 */ | |

pScr1 = pScratch; | |

/* Clear Accumlators */ | |

acc0 = 0; | |

acc1 = 0; | |

acc2 = 0; | |

acc3 = 0; | |

/* Read two samples from scratch buffer */ | |

x1 = read_q15x2_ia (&pScr1); | |

/* Read next two samples from scratch buffer */ | |

x2 = read_q15x2_ia (&pScr1); | |

tapCnt = (srcBLen) >> 2U; | |

while (tapCnt > 0U) | |

{ | |

/* Read four samples from smaller buffer */ | |

y1 = read_q15x2_ia ((q15_t **) &pIn2); | |

y2 = read_q15x2_ia ((q15_t **) &pIn2); | |

/* multiply and accumlate */ | |

acc0 = __SMLAD(x1, y1, acc0); | |

acc2 = __SMLAD(x2, y1, acc2); | |

/* pack input data */ | |

#ifndef ARM_MATH_BIG_ENDIAN | |

x3 = __PKHBT(x2, x1, 0); | |

#else | |

x3 = __PKHBT(x1, x2, 0); | |

#endif | |

/* multiply and accumlate */ | |

acc1 = __SMLADX(x3, y1, acc1); | |

/* Read next two samples from scratch buffer */ | |

x1 = read_q15x2_ia (&pScr1); | |

/* multiply and accumlate */ | |

acc0 = __SMLAD(x2, y2, acc0); | |

acc2 = __SMLAD(x1, y2, acc2); | |

/* pack input data */ | |

#ifndef ARM_MATH_BIG_ENDIAN | |

x3 = __PKHBT(x1, x2, 0); | |

#else | |

x3 = __PKHBT(x2, x1, 0); | |

#endif | |

acc3 = __SMLADX(x3, y1, acc3); | |

acc1 = __SMLADX(x3, y2, acc1); | |

x2 = read_q15x2_ia (&pScr1); | |

#ifndef ARM_MATH_BIG_ENDIAN | |

x3 = __PKHBT(x2, x1, 0); | |

#else | |

x3 = __PKHBT(x1, x2, 0); | |

#endif | |

acc3 = __SMLADX(x3, y2, acc3); | |

/* Decrement loop counter */ | |

tapCnt--; | |

} | |

/* Update scratch pointer for remaining samples of smaller length sequence */ | |

pScr1 -= 4U; | |

/* apply same above for remaining samples of smaller length sequence */ | |

tapCnt = (srcBLen) & 3U; | |

while (tapCnt > 0U) | |

{ | |

/* accumlate the results */ | |

acc0 += (*pScr1++ * *pIn2); | |

acc1 += (*pScr1++ * *pIn2); | |

acc2 += (*pScr1++ * *pIn2); | |

acc3 += (*pScr1++ * *pIn2++); | |

pScr1 -= 3U; | |

/* Decrement loop counter */ | |

tapCnt--; | |

} | |

blkCnt--; | |

/* Store the results in the accumulators in the destination buffer. */ | |

*pOut = (__SSAT(acc0 >> 15U, 16)); | |

pOut += inc; | |

*pOut = (__SSAT(acc1 >> 15U, 16)); | |

pOut += inc; | |

*pOut = (__SSAT(acc2 >> 15U, 16)); | |

pOut += inc; | |

*pOut = (__SSAT(acc3 >> 15U, 16)); | |

pOut += inc; | |

/* Initialization of inputB pointer */ | |

pIn2 = py; | |

pScratch += 4U; | |

} | |

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

blkCnt = (srcALen + srcBLen - 1U) & 0x3; | |

#else | |

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

blkCnt = (srcALen + srcBLen - 1U); | |

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

/* Calculate correlation for remaining samples of Bigger length sequence */ | |

while (blkCnt > 0) | |

{ | |

/* Initialze temporary scratch pointer as scratch1 */ | |

pScr1 = pScratch; | |

/* Clear Accumlators */ | |

acc0 = 0; | |

tapCnt = (srcBLen) >> 1U; | |

while (tapCnt > 0U) | |

{ | |

/* Read next two samples from scratch buffer */ | |

acc0 += (*pScr1++ * *pIn2++); | |

acc0 += (*pScr1++ * *pIn2++); | |

/* Decrement loop counter */ | |

tapCnt--; | |

} | |

tapCnt = (srcBLen) & 1U; | |

/* apply same above for remaining samples of smaller length sequence */ | |

while (tapCnt > 0U) | |

{ | |

/* accumlate the results */ | |

acc0 += (*pScr1++ * *pIn2++); | |

/* Decrement loop counter */ | |

tapCnt--; | |

} | |

blkCnt--; | |

/* The result is in 2.30 format. Convert to 1.15 with saturation. | |

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

*pOut = (q15_t) (__SSAT((acc0 >> 15), 16)); | |

pOut += inc; | |

/* Initialization of inputB pointer */ | |

pIn2 = py; | |

pScratch += 1U; | |

} | |

} | |

/** | |

@} end of Corr group | |

*/ |