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/* ----------------------------------------------------------------------
* Copyright (C) 2011 ARM Limited. All rights reserved.
*
* $Date: 15. February 2012
* $Revision: V1.1.0
*
* Project: CMSIS DSP Library
* Title: arm_sqrt_q31.c
*
* Description: Q31 square root function.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
* Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.0 2011/03/08
* Alpha release.
*
* Version 1.0.1 2011/09/30
* Beta release.
*
* -------------------------------------------------------------------- */
#include "arm_math.h"
#include "arm_common_tables.h"
/**
* @ingroup groupFastMath
*/
/**
* @addtogroup SQRT
* @{
*/
/**
* @brief Q31 square root function.
* @param[in] in input value. The range of the input value is [0 +1) or 0x00000000 to 0x7FFFFFFF.
* @param[out] *pOut square root of input value.
* @return The function returns ARM_MATH_SUCCESS if input value is positive value or ARM_MATH_ARGUMENT_ERROR if
* <code>in</code> is negative value and returns zero output for negative values.
*/
arm_status arm_sqrt_q31(
q31_t in,
q31_t * pOut)
{
q31_t number, temp1, bits_val1, var1, signBits1, half;
float32_t temp_float1;
number = in;
/* If the input is a positive number then compute the signBits. */
if(number > 0)
{
signBits1 = __CLZ(number) - 1;
/* 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 * 4.6566128731e-010f;
/*Store as integer */
bits_val1 = *(int *) &temp_float1;
/* Subtract the shifted value from the magic number to give intial guess */
bits_val1 = 0x5f3759df - (bits_val1 >> 1); // gives initial guess
/* Store as float */
temp_float1 = *(float *) &bits_val1;
/* Convert to integer format */
var1 = (q31_t) (temp_float1 * 1073741824);
/* 1st iteration */
var1 = ((q31_t) ((q63_t) var1 * (0x30000000 -
((q31_t)
((((q31_t)
(((q63_t) var1 * var1) >> 31)) *
(q63_t) half) >> 31))) >> 31)) << 2;
/* 2nd iteration */
var1 = ((q31_t) ((q63_t) var1 * (0x30000000 -
((q31_t)
((((q31_t)
(((q63_t) var1 * var1) >> 31)) *
(q63_t) half) >> 31))) >> 31)) << 2;
/* 3rd iteration */
var1 = ((q31_t) ((q63_t) var1 * (0x30000000 -
((q31_t)
((((q31_t)
(((q63_t) var1 * var1) >> 31)) *
(q63_t) half) >> 31))) >> 31)) << 2;
/* Multiply the inverse square root with the original value */
var1 = ((q31_t) (((q63_t) temp1 * var1) >> 31)) << 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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