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155 lines
5.1 KiB
155 lines
5.1 KiB
/* ----------------------------------------------------------------------
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* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
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*
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* $Date: 19. October 2015
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* $Revision: V.1.4.5 a
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*
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* Project: CMSIS DSP Library
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* Title: arm_sqrt_q15.c
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*
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* Description: Q15 square root function.
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*
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* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* - Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* - Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* - Neither the name of ARM LIMITED nor the names of its contributors
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* may be used to endorse or promote products derived from this
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* software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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* -------------------------------------------------------------------- */
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#include "arm_math.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 Q15 square root function.
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* @param[in] in input value. The range of the input value is [0 +1) or 0x0000 to 0x7FFF.
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* @param[out] *pOut square root of input value.
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* @return The function returns ARM_MATH_SUCCESS if the input value is positive
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* and ARM_MATH_ARGUMENT_ERROR if the input is negative. For
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* negative inputs, the function returns *pOut = 0.
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*/
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arm_status arm_sqrt_q15(
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q15_t in,
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q15_t * pOut)
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{
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q15_t number, temp1, var1, signBits1, half;
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q31_t bits_val1;
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float32_t temp_float1;
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union
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{
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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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{
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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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{
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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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/* 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 = ((q15_t) ((q31_t) var1 * (0x3000 -
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((q15_t)
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((((q15_t)
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(((q31_t) var1 * var1) >> 15)) *
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(q31_t) half) >> 15))) >> 15)) << 2;
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/* 2nd iteration */
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var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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((q15_t)
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((((q15_t)
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(((q31_t) var1 * var1) >> 15)) *
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(q31_t) half) >> 15))) >> 15)) << 2;
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/* 3rd iteration */
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var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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((q15_t)
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((((q15_t)
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(((q31_t) var1 * var1) >> 15)) *
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(q31_t) half) >> 15))) >> 15)) << 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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{
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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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