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/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_vlog_q31
* Description: Q31 vector log
*
* $Date: 19 July 2021
* $Revision: V1.10.0
*
* Target Processor: Cortex-M and Cortex-A cores
* -------------------------------------------------------------------- */
/*
* Copyright (C) 2010-2021 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 "dsp/fast_math_functions.h"
#define LOG_Q31_ACCURACY 31
/* Bit to represent the normalization factor
It is Ceiling[Log2[LOG_Q31_ACCURACY]] of the previous value.
The Log2 algorithm is assuming that the value x is
1 <= x < 2.
But input value could be as small a 2^-LOG_Q31_ACCURACY
which would give an integer part of -31.
*/
#define LOG_Q31_INTEGER_PART 5
/* 2.0 in Q30 */
#define LOQ_Q31_THRESHOLD (1u << LOG_Q31_ACCURACY)
/* HALF */
#define LOQ_Q31_Q32_HALF LOQ_Q31_THRESHOLD
#define LOQ_Q31_Q30_HALF (LOQ_Q31_Q32_HALF >> 2)
/* 1.0 / Log2[Exp[1]] in Q31 */
#define LOG_Q31_INVLOG2EXP 0x58b90bfbuL
/* Clay Turner algorithm */
static uint32_t arm_scalar_log_q31(uint32_t src)
{
int32_t i;
int32_t c = __CLZ(src);
int32_t normalization=0;
/* 0.5 in q26 */
uint32_t inc = LOQ_Q31_Q32_HALF >> (LOG_Q31_INTEGER_PART + 1);
/* Will compute y = log2(x) for 1 <= x < 2.0 */
uint32_t x;
/* q26 */
uint32_t y=0;
/* q26 */
int32_t tmp;
/* Normalize and convert to q30 format */
x = src;
if ((c-1) < 0)
{
x = x >> (1-c);
}
else
{
x = x << (c-1);
}
normalization = c;
/* Compute the Log2. Result is in q26
because we know 0 <= y < 1.0 but
do not want to use q32 to allow
following computation with less instructions.
*/
for(i = 0; i < LOG_Q31_ACCURACY ; i++)
{
x = ((int64_t)x*x) >> (LOG_Q31_ACCURACY - 1);
if (x >= LOQ_Q31_THRESHOLD)
{
y += inc ;
x = x >> 1;
}
inc = inc >> 1;
}
/*
Convert the Log2 to Log and apply normalization.
We compute (y - normalisation) * (1 / Log2[e]).
*/
/* q26 */
tmp = (int32_t)y - (normalization << (LOG_Q31_ACCURACY - LOG_Q31_INTEGER_PART));
/* q5.26 */
y = ((int64_t)tmp * LOG_Q31_INVLOG2EXP) >> 31;
return(y);
}
#if defined(ARM_MATH_MVEI) && !defined(ARM_MATH_AUTOVECTORIZE)
q31x4_t vlogq_q31(q31x4_t src)
{
int32_t i;
int32x4_t c = vclzq_s32(src);
int32x4_t normalization = c;
/* 0.5 in q11 */
uint32_t inc = LOQ_Q31_Q32_HALF >> (LOG_Q31_INTEGER_PART + 1);
/* Will compute y = log2(x) for 1 <= x < 2.0 */
uint32x4_t x;
/* q11 */
uint32x4_t y = vdupq_n_u32(0);
/* q11 */
int32x4_t vtmp;
mve_pred16_t p;
/* Normalize and convert to q14 format */
vtmp = vsubq_n_s32(c,1);
x = vshlq_u32((uint32x4_t)src,vtmp);
/* Compute the Log2. Result is in Q26
because we know 0 <= y < 1.0 but
do not want to use Q32 to allow
following computation with less instructions.
*/
for(i = 0; i < LOG_Q31_ACCURACY ; i++)
{
x = vmulhq_u32(x,x);
x = vshlq_n_u32(x,2);
p = vcmphiq_u32(x,vdupq_n_u32(LOQ_Q31_THRESHOLD));
y = vaddq_m_n_u32(y, y,inc,p);
x = vshrq_m_n_u32(x,x,1,p);
inc = inc >> 1;
}
/*
Convert the Log2 to Log and apply normalization.
We compute (y - normalisation) * (1 / Log2[e]).
*/
/* q11 */
// tmp = (int16_t)y - (normalization << (LOG_Q15_ACCURACY - LOG_Q15_INTEGER_PART));
vtmp = vshlq_n_s32(normalization,LOG_Q31_ACCURACY - LOG_Q31_INTEGER_PART);
vtmp = vsubq_s32((int32x4_t)y,vtmp);
/* q4.11 */
// y = ((int32_t)tmp * LOG_Q15_INVLOG2EXP) >> 15;
vtmp = vqdmulhq_n_s32(vtmp,LOG_Q31_INVLOG2EXP);
return(vtmp);
}
#endif
/**
@ingroup groupFastMath
*/
/**
@addtogroup vlog
@{
*/
/**
@brief q31 vector of log values.
@param[in] pSrc points to the input vector in q31
@param[out] pDst points to the output vector q5.26
@param[in] blockSize number of samples in each vector
@return none
*/
void arm_vlog_q31(
const q31_t * pSrc,
q31_t * pDst,
uint32_t blockSize)
{
uint32_t blkCnt; /* loop counters */
#if defined(ARM_MATH_MVEI) && !defined(ARM_MATH_AUTOVECTORIZE)
q31x4_t src;
q31x4_t dst;
blkCnt = blockSize >> 2;
while (blkCnt > 0U)
{
src = vld1q(pSrc);
dst = vlogq_q31(src);
vst1q(pDst, dst);
pSrc += 4;
pDst += 4;
/* Decrement loop counter */
blkCnt--;
}
blkCnt = blockSize & 3;
#else
blkCnt = blockSize;
#endif
while (blkCnt > 0U)
{
*pDst++=arm_scalar_log_q31(*pSrc++);
blkCnt--;
}
}
/**
@} end of vlog group
*/
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