src/math/floor.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 floor(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 = x - toint + toint - x;
	else
		y = x + toint - toint - x;
	/* special case because of non-nearest rounding modes */
	if (e <= 0x3ff-1) {
		FORCE_EVAL(y);
		return u.i >> 63 ? -1 : 0;
	}
	if (y > 0)
		return x + y - 1;
	return x + y;
}