127 lines
3.2 KiB
C
127 lines
3.2 KiB
C
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/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_sqrt_q31.c
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* Description: Q31 square root function
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*
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* $Date: 23 April 2021
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* $Revision: V1.9.0
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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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#include "dsp/fast_math_functions.h"
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#include "arm_common_tables.h"
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/**
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@ingroup groupFastMath
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*/
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/**
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@addtogroup SQRT
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@{
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*/
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/**
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@brief Q31 square root function.
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@param[in] in input value. The range of the input value is [0 +1) or 0x00000000 to 0x7FFFFFFF
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@param[out] pOut points to square root of input value
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@return execution status
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- \ref ARM_MATH_SUCCESS : input value is positive
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- \ref ARM_MATH_ARGUMENT_ERROR : input value is negative; *pOut is set to 0
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*/
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#define Q28QUARTER 0x20000000
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arm_status arm_sqrt_q31(
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q31_t in,
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q31_t * pOut)
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{
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q31_t number, var1, signBits1 ,temp;
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number = in;
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/* If the input is a positive number then compute the signBits. */
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if (number > 0)
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{
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signBits1 = __CLZ(number) - 1;
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/* Shift by the number of signBits1 */
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if ((signBits1 % 2) == 0)
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{
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number = number << signBits1;
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}
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else
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{
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number = number << (signBits1 - 1);
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}
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/* Start value for 1/sqrt(x) for the Newton iteration */
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var1 = sqrt_initial_lut_q31[(number>> 26) - (Q28QUARTER >> 26)];
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/* 0.5 var1 * (3 - number * var1 * var1) */
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/* 1st iteration */
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temp = ((q63_t) var1 * var1) >> 28;
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temp = ((q63_t) number * temp) >> 31;
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temp = 0x30000000 - temp;
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var1 = ((q63_t) var1 * temp) >> 29;
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/* 2nd iteration */
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temp = ((q63_t) var1 * var1) >> 28;
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temp = ((q63_t) number * temp) >> 31;
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temp = 0x30000000 - temp;
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var1 = ((q63_t) var1 * temp) >> 29;
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/* 3nd iteration */
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temp = ((q63_t) var1 * var1) >> 28;
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temp = ((q63_t) number * temp) >> 31;
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temp = 0x30000000 - temp;
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var1 = ((q63_t) var1 * temp) >> 29;
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/* Multiply the inverse square root with the original value */
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var1 = ((q31_t) (((q63_t) number * var1) >> 28));
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/* Shift the output down accordingly */
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if ((signBits1 % 2) == 0)
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{
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var1 = var1 >> (signBits1 / 2);
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}
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else
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{
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var1 = var1 >> ((signBits1 - 1) / 2);
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}
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*pOut = var1;
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return (ARM_MATH_SUCCESS);
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}
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/* If the number is a negative number then store zero as its square root value */
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else
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{
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*pOut = 0;
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return (ARM_MATH_ARGUMENT_ERROR);
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}
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}
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/**
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@} end of SQRT group
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*/
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