1 /* $NetBSD: s_scalbnl.c,v 1.1 2011/07/26 16:10:16 joerg Exp $ */ 2 3 /*- 4 * Copyright (c) 2011 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Joerg Sonnenberger. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 #include <sys/cdefs.h> 33 __RCSID("$NetBSD: s_scalbnl.c,v 1.1 2011/07/26 16:10:16 joerg Exp $"); 34 35 #include "namespace.h" 36 37 #include <float.h> 38 #include <math.h> 39 #include <machine/ieee.h> 40 41 #ifdef __HAVE_LONG_DOUBLE 42 43 #ifdef __weak_alias 44 __weak_alias(scalbnl, _scalbnl) 45 #endif 46 47 #if LDBL_MANT_DIG == 64 48 #define FROM_UNDERFLOW 0x1p65L 49 #define TO_UNDERFLOW 0x1p-65L 50 #elif LDBL_MANT_DIG == 113 51 #define FROM_UNDERFLOW 0x1p114L 52 #define TO_UNDERFLOW 0x1p-114L 53 #else 54 #error Unsupported long double format 55 #endif 56 57 long double 58 scalbnl(long double x, int n) 59 { 60 union ieee_ext_u u; 61 62 /* Trivial cases first */ 63 if (n == 0 || x == 0.0L) 64 return x; 65 66 u.extu_ld = x; 67 68 /* NaN and infinite don't change either, but trigger exception */ 69 if (u.extu_ext.ext_exp == EXT_EXP_INFNAN) 70 return x + x; 71 72 /* Protect against integer overflow in calculation of new exponent */ 73 if (n > LDBL_MAX_EXP - LDBL_MIN_EXP + LDBL_MANT_DIG) 74 goto overflow; 75 if (n < LDBL_MAX_EXP - LDBL_MIN_EXP + LDBL_MANT_DIG) 76 goto underflow; 77 78 /* Scale denormalized numbers slightly, so that they are normal */ 79 if (u.extu_ext.ext_exp == 0) { 80 u.extu_ld *= FROM_UNDERFLOW; 81 n -= LDBL_MANT_DIG + 1; 82 } 83 84 n += u.extu_ext.ext_exp; 85 if (n >= LDBL_MAX_EXP + EXT_EXP_BIAS) 86 goto overflow; 87 /* Positive exponent (incl. bias) means normal result */ 88 if (n > 0) { 89 u.extu_ext.ext_exp = n; 90 return u.extu_ld; 91 } 92 /* Shift the exponent and let the multiply below handle subnormal */ 93 n += LDBL_MANT_DIG + 1; 94 if (n <= 0) 95 goto underflow; 96 u.extu_ext.ext_exp = n; 97 return u.extu_ld * TO_UNDERFLOW; 98 99 underflow: 100 return LDBL_MIN * copysignl(LDBL_MIN, x); 101 102 overflow: 103 return LDBL_MAX * copysignl(LDBL_MAX, x); 104 } 105 106 #endif 107