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arm_sqrt_q31.c
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 r16 /* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date: 29. November 2010
* $Revision: V1.0.3
*
* Project: CMSIS DSP Library
* Title: arm_sqrt_q31.c
*
* Description: Q31 square root function.
*
* Target Processor: Cortex-M4/Cortex-M3
*
* Version 1.0.3 2010/11/29
* Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
* Documentation updated.
*
* Version 1.0.1 2010/10/05
* Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
* Production release and review comments incorporated.
* -------------------------------------------------------------------- */
#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)
{
q63_t out;
q63_t prevOut;
q31_t oneByOut;
uint32_t signBits;
if(in > 0)
{
/* run for ten iterations */
/* Take initial guess as half of the input and first iteration */
out = (in >> 1) + 0x3FFFFFFF;
/* Calculation of reciprocal of out */
/* oneByOut contains reciprocal of out which is in 2.30 format
and oneByOut should be upscaled by signBits */
signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
/* 0.5 * (out) */
out = out >> 1u;
/* prevOut = 0.5 * out + (in * (oneByOut << signBits))) */
prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
/* Third iteration */
signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
prevOut = prevOut >> 1u;
out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
out = out >> 1u;
prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
/* Fifth iteration */
signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
prevOut = prevOut >> 1u;
out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
out = out >> 1u;
prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
/* Seventh iteration */
signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
prevOut = prevOut >> 1u;
out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
out = out >> 1u;
prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
prevOut = prevOut >> 1u;
out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
/* tenth iteration */
signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
out = out >> 1u;
*pOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
return (ARM_MATH_SUCCESS);
}
else
{
*pOut = 0;
return (ARM_MATH_ARGUMENT_ERROR);
}
}
/**
* @} end of SQRT group
*/