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      1 /*	$NetBSD: s_rintl.c,v 1.7 2024/05/04 19:21:51 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2008 David Schultz <das (at) FreeBSD.ORG>
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     26  * SUCH DAMAGE.
     27  */
     28 
     29 #include <sys/cdefs.h>
     30 #if 0
     31 __FBSDID("$FreeBSD: src/lib/msun/src/s_rintl.c,v 1.5 2008/02/22 11:59:05 bde Exp $");
     32 #else
     33 __RCSID("$NetBSD: s_rintl.c,v 1.7 2024/05/04 19:21:51 riastradh Exp $");
     34 #endif
     35 
     36 #include <float.h>
     37 #include <machine/ieee.h>
     38 
     39 #include "math.h"
     40 #include "math_private.h"
     41 
     42 #define	BIAS	(LDBL_MAX_EXP - 1)
     43 
     44 static const float
     45 shift[2] = {
     46 #if LDBL_MANT_DIG == 64
     47 	0x1.0p63, -0x1.0p63
     48 #elif LDBL_MANT_DIG == 113
     49 	0x1.0p112, -0x1.0p112
     50 #else
     51 #error "Unsupported long double format"
     52 #endif
     53 };
     54 static const float zero[2] = { 0.0, -0.0 };
     55 
     56 long double
     57 rintl(long double x)
     58 {
     59 	union ieee_ext_u u;
     60 	uint32_t expsign;
     61 	int ex, sign;
     62 
     63 	u.extu_ld = x;
     64 	expsign = GET_EXPSIGN(&u);
     65 	ex = expsign & 0x7fff;
     66 
     67 	if (ex >= BIAS + LDBL_MANT_DIG - 1) {
     68 		if (ex == BIAS + LDBL_MAX_EXP)
     69 			return (x + x);	/* Inf, NaN, or unsupported format */
     70 		return (x);		/* finite and already an integer */
     71 	}
     72 	sign = expsign >> 15;
     73 
     74 	/*
     75 	 * The following code assumes that intermediate results are
     76 	 * evaluated in long double precision. If they are evaluated in
     77 	 * greater precision, double rounding may occur, and if they are
     78 	 * evaluated in less precision (as on i386), results will be
     79 	 * wildly incorrect.
     80 	 */
     81 	x += shift[sign];
     82 	x -= shift[sign];
     83 
     84 	/*
     85 	 * If the result is +-0, then it must have the same sign as x, but
     86 	 * the above calculation doesn't always give this.  Fix up the sign.
     87 	 */
     88 	if (ex < BIAS && x == 0.0L)
     89 		return (zero[sign]);
     90 
     91 	return (x);
     92 }
     93