V7/usr/src/libm/floor.c

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/*
 * floor and ceil-- greatest integer <= arg
 * (resp least >=)
 */

double	modf();

double
floor(d)
double d;
{
	double fract;

	if (d<0.0) {
		d = -d;
		fract = modf(d, &d);
		if (fract != 0.0)
			d += 1;
		d = -d;
	} else
		modf(d, &d);
	return(d);
}

double
ceil(d)
double d;
{
	return(-floor(-d));
}