musl/src/math/ceil.c

#include "libm.h"

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

	if (e >= 0x3ff+52 || x == 0)
		return x;
	/* y = int(x) - x, where int(x) is an integer neighbor of x */
	if (u.i >> 63)
		y = (double)(x - 0x1p52) + 0x1p52 - x;
	else
		y = (double)(x + 0x1p52) - 0x1p52 - x;
	/* special case because of non-nearest rounding modes */
	if (e <= 0x3ff-1) {
		FORCE_EVAL(y);
		return u.i >> 63 ? -0.0 : 1;
	}
	if (y < 0)
		return x + y + 1;
	return x + y;
}