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174 lines
3.8 KiB
C
174 lines
3.8 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_vlog_q31
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* Description: Q31 vector log
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*
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* $Date: 19 July 2021
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* $Revision: V1.10.0
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*
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* Target Processor: Cortex-M and Cortex-A cores
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* -------------------------------------------------------------------- */
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/*
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* Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved.
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the License); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an AS IS BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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This is a first attempt at implement a log in Q31
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without using an interpolation table since there are
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already too many tables in CMSIS-DSP.
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But the accuracy is not that great for very small values ...
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*/
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#include "dsp/fast_math_functions.h"
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#define LOG_Q31_ACCURACY 31
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/* Bit to represent the normalization factor
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It is Ceiling[Log2[LOG_Q31_ACCURACY]] of the previous value.
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The Log2 algorithm is assuming that the value x is
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1 <= x < 2.
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But input value could be as small a 2^-LOG_Q31_ACCURACY
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which would give an integer part of -31.
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*/
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#define LOG_Q31_INTEGER_PART 5
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/* 2.0 in Q30 or 0.5 in Q32 */
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#define LOQ_Q31_THRESHOLD (1u << LOG_Q31_ACCURACY)
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#define LOQ_Q31_Q32_HALF LOQ_Q31_THRESHOLD
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#define LOQ_Q31_Q30_HALF (LOQ_Q31_Q32_HALF >> 2)
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/* 1.0 / Log2[Exp[1]] in Q31 */
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#define LOG_Q31_INVLOG2EXP 0x58b90bfbuL
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/* Clay Turner algorithm */
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static uint32_t arm_scalar_log_q31(uint32_t src)
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{
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int i;
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int32_t c = __CLZ(src);
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int32_t normalization=0;
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//printf("x q31 = %08X\n",src);
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/* 0.5 in q32 */
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uint32_t inc = LOQ_Q31_Q32_HALF;
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/* Will compute y = log2(x) for 1 <= x < 2.0 */
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uint64_t x;
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/* q32 */
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uint32_t y=0;
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/* q5.58 */
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int64_t tmp;
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/* Normalize and convert to q30 format */
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x = src;
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if ((c-1) < 0)
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{
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x = x >> (1-c);
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}
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else
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{
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x = x << (c-1);
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}
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normalization = c;
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//printf("normalization = %d\n",normalization);
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//printf("x normalized q30 = %08llX\n",x);
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/* Compute the Log2. Result is in Q32
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because we know 0 <= y < 1.0
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*/
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for(i = 0; i < LOG_Q31_ACCURACY ; i++)
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{
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x = ((x*x) + LOQ_Q31_Q30_HALF) >> (LOG_Q31_ACCURACY - 1);
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if (x >= LOQ_Q31_THRESHOLD)
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{
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y += inc ;
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x = x >> 1;
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}
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inc = inc >> 1;
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}
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//printf("Log2 q32 = %08X\n",y);
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/*
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Convert the Log2 to Log and apply normalization.
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We compute (y - normalisation) * (1 / Log2[e]).
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*/
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/* q32 */
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tmp = y - ((int64_t)normalization << (LOG_Q31_ACCURACY + 1));
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//printf("Log2 q32 with normalization = %016llX\n",tmp);
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/* q27 * q31 -> q58 */
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tmp = (tmp>>LOG_Q31_INTEGER_PART) * (int64_t)LOG_Q31_INVLOG2EXP ;
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//printf("Log10 q58 = %016llX\n",tmp);
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/* q5.26 */
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y = tmp >> 32;
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//printf("Log10 q25 = %08X\n",y);
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return(y);
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}
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/**
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@ingroup groupFastMath
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*/
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/**
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@addtogroup vlog
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@{
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*/
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/**
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@brief q31 vector of log values.
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@param[in] pSrc points to the input vector in q31
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@param[out] pDst points to the output vector q5.26
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@param[in] blockSize number of samples in each vector
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@return none
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*/
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void arm_vlog_q31(
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const q31_t * pSrc,
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q31_t * pDst,
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uint32_t blockSize)
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{
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uint32_t i;
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for(i=0;i < blockSize; i++)
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{
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pDst[i]=arm_scalar_log_q31(pSrc[i]);
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}
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}
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/**
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@} end of vlog group
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*/
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