142 lines
4.0 KiB
C
142 lines
4.0 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_sqrt_q15.c
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* Description: Q15 square root function
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*
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* $Date: 18. March 2019
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* $Revision: V1.6.0
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*
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* Target Processor: Cortex-M cores
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* -------------------------------------------------------------------- */
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/*
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* Copyright (C) 2010-2019 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 "arm_common_tables.h"
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#include "arm_math.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 Q15 square root function.
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@param[in] in input value. The range of the input value is [0 +1) or
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0x0000 to 0x7FFF
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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;
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*pOut is set to 0
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*/
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arm_status arm_sqrt_q15(q15_t in, q15_t *pOut) {
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q31_t bits_val1;
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q15_t number, temp1, var1, signBits1, half;
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float32_t temp_float1;
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union {
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q31_t fracval;
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float32_t floatval;
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} tempconv;
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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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signBits1 = __CLZ(number) - 17;
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/* Shift by the number of signBits1 */
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if ((signBits1 % 2) == 0) {
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number = number << signBits1;
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} else {
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number = number << (signBits1 - 1);
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}
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/* Calculate half value of the number */
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half = number >> 1;
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/* Store the number for later use */
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temp1 = number;
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/* Convert to float */
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temp_float1 = number * 3.051757812500000e-005f;
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/* Store as integer */
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tempconv.floatval = temp_float1;
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bits_val1 = tempconv.fracval;
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/* Subtract the shifted value from the magic number to give intial guess */
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bits_val1 = 0x5f3759df - (bits_val1 >> 1); /* gives initial guess */
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/* Store as float */
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tempconv.fracval = bits_val1;
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temp_float1 = tempconv.floatval;
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/* Convert to integer format */
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var1 = (q31_t)(temp_float1 * 16384);
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/* 1st iteration */
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var1 =
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((q15_t)((q31_t)var1 *
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(0x3000 - ((q15_t)((((q15_t)(((q31_t)var1 * var1) >> 15)) *
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(q31_t)half) >>
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15))) >>
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15))
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<< 2;
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/* 2nd iteration */
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var1 =
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((q15_t)((q31_t)var1 *
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(0x3000 - ((q15_t)((((q15_t)(((q31_t)var1 * var1) >> 15)) *
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(q31_t)half) >>
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15))) >>
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15))
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<< 2;
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/* 3rd iteration */
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var1 =
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((q15_t)((q31_t)var1 *
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(0x3000 - ((q15_t)((((q15_t)(((q31_t)var1 * var1) >> 15)) *
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(q31_t)half) >>
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15))) >>
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15))
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<< 2;
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/* Multiply the inverse square root with the original value */
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var1 = ((q15_t)(((q31_t)temp1 * var1) >> 15)) << 1;
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/* Shift the output down accordingly */
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if ((signBits1 % 2) == 0) {
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var1 = var1 >> (signBits1 / 2);
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} else {
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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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*/
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else {
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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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