aversive_10-03-12/modules/base/math/fixed_point/f16_sqrt.c

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/*  
 *  Copyright Droids Corporation, Microb Technology, Eirbot (2005)
 * 
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 *  Revision : $Id: f16_sqrt.c,v 1.8 2009-03-15 21:51:16 zer0 Exp $
 *
 */

#include <stdio.h>
#include <f16.h>
#include <s16_to_f16.h>


#define NEXT(n, i)  (((n) + (i)/(n)) >> 1)

static uint16_t u16_sqrt(uint16_t number) {
        uint16_t n  = 1;
        uint16_t n1 = NEXT(n, number);
        
        if (number == 0)
                return 0;

        while(ABS(n1 - n) > 1) {
                n  = n1;
                n1 = NEXT(n, number);
        }
        while((n1*n1) > number) {
                n1 -= 1;
        }
        return n1;
}


f16 f16_sqrt(f16 f)
{
        uint16_t a,b,c,d;

        if (F16_IS_NEG(f))
                return F16_NAN;

        if(f.f16_integer) {
                /* sqrt(a+b) = sqrt(a)*sqrt(1+b/a) */
                a=(uint16_t)(f.f16_integer) << 8 ;
                b=(uint16_t)(f.f16_decimal) << 8 ;
                c=u16_sqrt(a);
                d=u16_sqrt(0x100 + (b/a));
                return f16_mul(s16_to_f16( c<<4 ), s16_to_f16( d<<4 ));
        }
        else {
                b=(uint16_t)(f.f16_decimal) << 8 ;
                return s16_to_f16(u16_sqrt(b));
        }
}

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