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173 lines
3.8 KiB
C
173 lines
3.8 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_vlog_q15
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* Description: Q15 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 Q15
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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_Q15_ACCURACY 15
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/* Bit to represent the normalization factor
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It is Ceiling[Log2[LOG_Q15_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_Q15_ACCURACY
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which would give an integer part of -15.
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*/
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#define LOG_Q15_INTEGER_PART 4
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/* 2.0 in Q14 or 0.5 in Q16 */
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#define LOQ_Q15_THRESHOLD (1u << LOG_Q15_ACCURACY)
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#define LOQ_Q15_Q16_HALF LOQ_Q15_THRESHOLD
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#define LOQ_Q15_Q14_HALF (LOQ_Q15_Q16_HALF >> 2)
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/* 1.0 / Log2[Exp[1]] in Q15 */
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#define LOG_Q15_INVLOG2EXP 0x58b9u
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/* Clay Turner algorithm */
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static uint16_t arm_scalar_log_q15(uint16_t src)
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{
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int i;
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int32_t c = __CLZ(src)-16;
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int16_t normalization=0;
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//printf("x q15 = %08X, c = %d\n",src,c);
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/* 0.5 in q16 */
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uint16_t inc = LOQ_Q15_Q16_HALF;
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/* Will compute y = log2(x) for 1 <= x < 2.0 */
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uint32_t x;
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/* q16 */
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uint16_t y=0;
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/* q4.24 */
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int32_t tmp;
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/* Normalize and convert to q14 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 q14 = %08X\n",x);
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/* Compute the Log2. Result is in Q16
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because we know 0 <= y < 1.0
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*/
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for(i = 0; i < LOG_Q15_ACCURACY ; i++)
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{
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x = ((x*x) + LOQ_Q15_Q14_HALF) >> (LOG_Q15_ACCURACY - 1);
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if (x >= LOQ_Q15_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 q16 = %04X\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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/* q16 */
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tmp = y - ((int32_t)normalization << (LOG_Q15_ACCURACY + 1));
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//printf("Log2 q16 with normalization = %08X\n",tmp);
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/* q12 * q15 -> q27 */
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tmp = (tmp>>LOG_Q15_INTEGER_PART) * (int32_t)LOG_Q15_INVLOG2EXP ;
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//printf("Log10 q27 = %08X\n",tmp);
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/* q4.11 */
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y = tmp >> 16;
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//printf("Log10 q11 = %04X\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 q15 vector of log values.
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@param[in] pSrc points to the input vector in q15
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@param[out] pDst points to the output vector in q4.11
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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_q15(
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const q15_t * pSrc,
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q15_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_q15(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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