1 /* $OpenBSD: s_rintl.c,v 1.1 2008/12/09 20:00:35 martynas Exp $ */ 2 /*- 3 * Copyright (c) 2008 David Schultz <das@FreeBSD.ORG> 4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25 * SUCH DAMAGE. 26 */ 27 28 #include <sys/types.h> 29 #include <machine/ieee.h> 30 #include <float.h> 31 #include <math.h> 32 33 #if LDBL_MAX_EXP != 0x4000 34 /* We also require the usual bias, min exp and expsign packing. */ 35 #error "Unsupported long double format" 36 #endif 37 38 #define BIAS (LDBL_MAX_EXP - 1) 39 40 static const float 41 shift[2] = { 42 #if LDBL_MANT_DIG == 64 43 0x1.0p63, -0x1.0p63 44 #elif LDBL_MANT_DIG == 113 45 0x1.0p112, -0x1.0p112 46 #else 47 #error "Unsupported long double format" 48 #endif 49 }; 50 static const float zero[2] = { 0.0, -0.0 }; 51 52 long double 53 rintl(long double x) 54 { 55 union { 56 long double e; 57 struct ieee_ext bits; 58 } u; 59 uint32_t expsign; 60 int ex, sign; 61 62 u.e = x; 63 expsign = (u.bits.ext_sign << 15) | u.bits.ext_exp; 64 ex = expsign & 0x7fff; 65 66 if (ex >= BIAS + LDBL_MANT_DIG - 1) { 67 if (ex == BIAS + LDBL_MAX_EXP) 68 return (x + x); /* Inf, NaN, or unsupported format */ 69 return (x); /* finite and already an integer */ 70 } 71 sign = expsign >> 15; 72 73 /* 74 * The following code assumes that intermediate results are 75 * evaluated in long double precision. If they are evaluated in 76 * greater precision, double rounding may occur, and if they are 77 * evaluated in less precision (as on i386), results will be 78 * wildly incorrect. 79 */ 80 x += shift[sign]; 81 x -= shift[sign]; 82 83 /* 84 * If the result is +-0, then it must have the same sign as x, but 85 * the above calculation doesn't always give this. Fix up the sign. 86 */ 87 if (ex < BIAS && x == 0.0L) 88 return (zero[sign]); 89 90 return (x); 91 } 92