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#include <u.h>
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#include <libc.h>
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#include "map.h"
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double
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cubrt(double a)
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{
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	double x,y,x1;
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	if(a==0)
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		return(0.);
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	y = 1;
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	if(a<0) {
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		y = -y;
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		a = -a;
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	}
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	while(a<1) {
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		a *= 8;
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		y /= 2;
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	}
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	while(a>1) {
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		a /= 8;
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		y *= 2;
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	}
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	x = 1;
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	do {
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		x1 = x;
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		x = (2*x1+a/(x1*x1))/3;
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	} while(fabs(x-x1)>10.e-15);
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	return(x*y);
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}