lib/libm/src/lrint.c
/* $NetBSD: lrint.c,v 1.4 2008/04/26 23:49:50 christos Exp $ */

/*-
 * Copyright (c) 2004
 *	Matthias Drochner. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <math.h>
#include <sys/ieee754.h>
#include <machine/limits.h>
#include "math_private.h"

#ifndef LRINTNAME
#define LRINTNAME lrint
#define RESTYPE long int
#define RESTYPE_MIN LONG_MIN
#define RESTYPE_MAX LONG_MAX
#endif

#define RESTYPE_BITS (sizeof(RESTYPE) * 8)

static const double
TWO52[2]={
  4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
};

RESTYPE
LRINTNAME(double x)
{
	u_int32_t i0, i1;
	int e, s, shift;
	RESTYPE res;

	GET_HIGH_WORD(i0, x);
	e = i0 >> 20;
	s = (uint32_t)e >> DBL_EXPBITS;
	e = (e & 0x7ff) - DBL_EXP_BIAS;

	/* 1.0 x 2^-1 is the smallest number which can be rounded to 1 */
	if (e < -1)
		return (0);
	/* 1.0 x 2^31 (or 2^63) is already too large */
	if (e >= (int)RESTYPE_BITS - 1)
		return (s ? RESTYPE_MIN : RESTYPE_MAX); /* ??? unspecified */

	/* >= 2^52 is already an exact integer */
	if (e < DBL_FRACBITS) {
		/* round, using current direction */
		x += TWO52[s];
		x -= TWO52[s];
	}

	EXTRACT_WORDS(i0, i1, x);
	e = ((i0 >> 20) & 0x7ff) - DBL_EXP_BIAS;
	i0 &= 0xfffff;
	i0 |= (1 << 20);

	shift = e - DBL_FRACBITS;
	if (shift >=0)
		res = (shift < 32 ? (RESTYPE)i1 << shift : 0);
	else
		res = (shift > -32 ? i1 >> -shift : 0);
	shift += 32;
	if (shift >=0)
		res |= (shift < 32 ? (RESTYPE)i0 << shift : 0);
	else
		res |= (shift > -32 ? i0 >> -shift : 0);

	return (s ? -res : res);
}
