s_rintl.c revision 176456
1/*- 2 * Copyright (c) 2008 David Schultz <das@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: head/lib/msun/src/s_rintl.c 176456 2008-02-22 09:21:14Z bde $"); 29 30#include <float.h> 31#include <math.h> 32 33#include "fpmath.h" 34 35#define BIAS (LDBL_MAX_EXP - 1) 36 37static const float 38shift[2] = { 39#if LDBL_MANT_DIG == 64 40 0x1.0p63, -0x1.0p63 41#elif LDBL_MANT_DIG == 113 42 0x1.0p112, -0x1.0p112 43#else 44#error "Unsupported long double format" 45#endif 46}; 47 48long double 49rintl(long double x) 50{ 51 union IEEEl2bits u; 52 short sign; 53 54 u.e = x; 55 56 if (u.bits.exp >= BIAS + LDBL_MANT_DIG - 1) { 57 if (u.bits.exp == BIAS + LDBL_MAX_EXP) 58 return (x + x); /* Inf, NaN, or unsupported format */ 59 return (x); /* finite and already an integer */ 60 } 61 sign = u.bits.sign; 62 63 /* 64 * The following code assumes that intermediate results are 65 * evaluated in long double precision. If they are evaluated in 66 * greater precision, double rounding may occur, and if they are 67 * evaluated in less precision (as on i386), results will be 68 * wildly incorrect. 69 */ 70 x += shift[sign]; 71 x -= shift[sign]; 72 73 /* 74 * If the result is +-0, then it must have the same sign as x, but 75 * the above calculation doesn't always give this. Fix up the sign. 76 */ 77 if (x == 0.0L) 78 return (sign ? -0.0L : 0.0L); 79 return (x); 80} 81