lib/libm/round.c


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#include "libm.h"

#if FLT_EVAL_METHOD == 0 || FLT_EVAL_METHOD == 1
#define EPS DBL_EPSILON
#elif FLT_EVAL_METHOD == 2
#define EPS LDBL_EPSILON
#endif
static const double_t toint = 1 / EPS;

double round(double x)
{
	union {
		double f;
		uint64_t i;
	} u = { x };
	int e = u.i >> 52 & 0x7ff;
	double_t y;

	if (e >= 0x3ff + 52)
		return x;
	if (u.i >> 63)
		x = -x;
	if (e < 0x3ff - 1) {
		/* raise inexact if x!=0 */
		FORCE_EVAL(x + toint);
		return 0 * u.f;
	}
	y = x + toint - toint - x;
	if (y > 0.5)
		y = y + x - 1;
	else if (y <= -0.5)
		y = y + x + 1;
	else
		y = y + x;
	if (u.i >> 63)
		y = -y;
	return y;
}