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/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_sqrt_q15.c
* Description: Q15 square root function
*
* $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"
#include "arm_common_tables.h"
/**
@ingroup groupFastMath
*/
/**
@addtogroup SQRT
@{
*/
/**
@brief Q15 square root function.
@param[in] in input value. The range of the input value is [0 +1) or 0x0000 to 0x7FFF
@param[out] pOut points to square root of input value
@return execution status
- \ref ARM_MATH_SUCCESS : input value is positive
- \ref ARM_MATH_ARGUMENT_ERROR : input value is negative; *pOut is set to 0
*/
arm_status arm_sqrt_q15(
q15_t in,
q15_t * pOut)
{
q31_t bits_val1;
q15_t number, temp1, var1, signBits1, half;
float32_t temp_float1;
union
{
q31_t fracval;
float32_t floatval;
} tempconv;
number = in;
/* If the input is a positive number then compute the signBits. */
if (number > 0)
{
signBits1 = __CLZ(number) - 17;
/* Shift by the number of signBits1 */
if ((signBits1 % 2) == 0)
{
number = number << signBits1;
}
else
{
number = number << (signBits1 - 1);
}
/* Calculate half value of the number */
half = number >> 1;
/* Store the number for later use */
temp1 = number;
/* Convert to float */
temp_float1 = number * 3.051757812500000e-005f;
/* Store as integer */
tempconv.floatval = temp_float1;
bits_val1 = tempconv.fracval;
/* Subtract the shifted value from the magic number to give intial guess */
bits_val1 = 0x5f3759df - (bits_val1 >> 1); /* gives initial guess */
/* Store as float */
tempconv.fracval = bits_val1;
temp_float1 = tempconv.floatval;
/* Convert to integer format */
var1 = (q31_t) (temp_float1 * 16384);
/* 1st iteration */
var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
((q15_t)
((((q15_t)
(((q31_t) var1 * var1) >> 15)) *
(q31_t) half) >> 15))) >> 15)) << 2;
/* 2nd iteration */
var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
((q15_t)
((((q15_t)
(((q31_t) var1 * var1) >> 15)) *
(q31_t) half) >> 15))) >> 15)) << 2;
/* 3rd iteration */
var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
((q15_t)
((((q15_t)
(((q31_t) var1 * var1) >> 15)) *
(q31_t) half) >> 15))) >> 15)) << 2;
/* Multiply the inverse square root with the original value */
var1 = ((q15_t) (((q31_t) temp1 * var1) >> 15)) << 1;
/* Shift the output down accordingly */
if ((signBits1 % 2) == 0)
{
var1 = var1 >> (signBits1 / 2);
}
else
{
var1 = var1 >> ((signBits1 - 1) / 2);
}
*pOut = var1;
return (ARM_MATH_SUCCESS);
}
/* If the number is a negative number then store zero as its square root value */
else
{
*pOut = 0;
return (ARM_MATH_ARGUMENT_ERROR);
}
}
/**
@} end of SQRT group
*/
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