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      1 /*-
      2  * Copyright (c) 2008 David Schultz <das (at) FreeBSD.ORG>
      3  * All rights reserved.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions
      7  * are met:
      8  * 1. Redistributions of source code must retain the above copyright
      9  *    notice, this list of conditions and the following disclaimer.
     10  * 2. Redistributions in binary form must reproduce the above copyright
     11  *    notice, this list of conditions and the following disclaimer in the
     12  *    documentation and/or other materials provided with the distribution.
     13  *
     14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     24  * SUCH DAMAGE.
     25  */
     26 
     27 #include <sys/cdefs.h>
     28 __FBSDID("$FreeBSD$");
     29 
     30 #include <float.h>
     31 #include <math.h>
     32 
     33 #include "fpmath.h"
     34 
     35 #if LDBL_MAX_EXP != 0x4000
     36 /* We also require the usual bias, min exp and expsign packing. */
     37 #error "Unsupported long double format"
     38 #endif
     39 
     40 #define	BIAS	(LDBL_MAX_EXP - 1)
     41 
     42 static const float
     43 shift[2] = {
     44 #if LDBL_MANT_DIG == 64
     45 	0x1.0p63, -0x1.0p63
     46 #elif LDBL_MANT_DIG == 113
     47 	0x1.0p112, -0x1.0p112
     48 #else
     49 #error "Unsupported long double format"
     50 #endif
     51 };
     52 static const float zero[2] = { 0.0, -0.0 };
     53 
     54 long double
     55 rintl(long double x)
     56 {
     57 	union IEEEl2bits u;
     58 	uint32_t expsign;
     59 	int ex, sign;
     60 
     61 	u.e = x;
     62 	expsign = u.xbits.expsign;
     63 	ex = expsign & 0x7fff;
     64 
     65 	if (ex >= BIAS + LDBL_MANT_DIG - 1) {
     66 		if (ex == BIAS + LDBL_MAX_EXP)
     67 			return (x + x);	/* Inf, NaN, or unsupported format */
     68 		return (x);		/* finite and already an integer */
     69 	}
     70 	sign = expsign >> 15;
     71 
     72 	/*
     73 	 * The following code assumes that intermediate results are
     74 	 * evaluated in long double precision. If they are evaluated in
     75 	 * greater precision, double rounding may occur, and if they are
     76 	 * evaluated in less precision (as on i386), results will be
     77 	 * wildly incorrect.
     78 	 */
     79 	x += shift[sign];
     80 	x -= shift[sign];
     81 
     82 	/*
     83 	 * If the result is +-0, then it must have the same sign as x, but
     84 	 * the above calculation doesn't always give this.  Fix up the sign.
     85 	 */
     86 	if (ex < BIAS && x == 0.0L)
     87 		return (zero[sign]);
     88 
     89 	return (x);
     90 }
     91