1 /* $NetBSD: compat_ldexp_ieee754.c,v 1.1 2006/06/27 18:16:47 drochner Exp $ */ 2 3 /*- 4 * Copyright (c) 1999 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Charles M. Hannum. 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 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the NetBSD 21 * Foundation, Inc. and its contributors. 22 * 4. Neither the name of The NetBSD Foundation nor the names of its 23 * contributors may be used to endorse or promote products derived 24 * from this software without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 29 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 36 * POSSIBILITY OF SUCH DAMAGE. 37 */ 38 39 #include <sys/cdefs.h> 40 #if defined(LIBC_SCCS) && !defined(lint) 41 __RCSID("$NetBSD: compat_ldexp_ieee754.c,v 1.1 2006/06/27 18:16:47 drochner Exp $"); 42 #endif /* LIBC_SCCS and not lint */ 43 44 #include <sys/types.h> 45 #include <machine/ieee.h> 46 #include <errno.h> 47 #include <math.h> 48 49 /* 50 * Multiply the given value by 2^expon. 51 */ 52 double 53 ldexp(double val, int expon) 54 { 55 int oldexp, newexp; 56 union ieee_double_u u, mul; 57 58 u.dblu_d = val; 59 oldexp = u.dblu_dbl.dbl_exp; 60 61 /* 62 * If input is zero, Inf or NaN, just return it. 63 */ 64 if (u.dblu_d == 0.0 || oldexp == DBL_EXP_INFNAN) 65 return (val); 66 67 if (oldexp == 0) { 68 /* 69 * u.v is denormal. We must adjust it so that the exponent 70 * arithmetic below will work. 71 */ 72 if (expon <= DBL_EXP_BIAS) { 73 /* 74 * Optimization: if the scaling can be done in a single 75 * multiply, or underflows, just do it now. 76 */ 77 if (expon <= -DBL_FRACBITS) { 78 errno = ERANGE; 79 return (val < 0.0 ? -0.0 : 0.0); 80 } 81 mul.dblu_d = 0.0; 82 mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS; 83 u.dblu_d *= mul.dblu_d; 84 if (u.dblu_d == 0.0) { 85 errno = ERANGE; 86 return (val < 0.0 ? -0.0 : 0.0); 87 } 88 return (u.dblu_d); 89 } else { 90 /* 91 * We know that expon is very large, and therefore the 92 * result cannot be denormal (though it may be Inf). 93 * Shift u.v by just enough to make it normal. 94 */ 95 mul.dblu_d = 0.0; 96 mul.dblu_dbl.dbl_exp = DBL_FRACBITS + DBL_EXP_BIAS; 97 u.dblu_d *= mul.dblu_d; 98 expon -= DBL_FRACBITS; 99 oldexp = u.dblu_dbl.dbl_exp; 100 } 101 } 102 103 /* 104 * u.v is now normalized and oldexp has been adjusted if necessary. 105 * Calculate the new exponent and check for underflow and overflow. 106 */ 107 newexp = oldexp + expon; 108 109 if (newexp <= 0) { 110 /* 111 * The output number is either denormal or underflows (see 112 * comments in machine/ieee.h). 113 */ 114 if (newexp <= -DBL_FRACBITS) { 115 errno = ERANGE; 116 return (val < 0.0 ? -0.0 : 0.0); 117 } 118 /* 119 * Denormalize the result. We do this with a multiply. If 120 * expon is very large, it won't fit in a double, so we have 121 * to adjust the exponent first. This is safe because we know 122 * that u.v is normal at this point. 123 */ 124 if (expon <= -DBL_EXP_BIAS) { 125 u.dblu_dbl.dbl_exp = 1; 126 expon += oldexp - 1; 127 } 128 mul.dblu_d = 0.0; 129 mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS; 130 u.dblu_d *= mul.dblu_d; 131 return (u.dblu_d); 132 } else if (newexp >= DBL_EXP_INFNAN) { 133 /* 134 * The result overflowed; return +/-Inf. 135 */ 136 u.dblu_dbl.dbl_exp = DBL_EXP_INFNAN; 137 u.dblu_dbl.dbl_frach = 0; 138 u.dblu_dbl.dbl_fracl = 0; 139 errno = ERANGE; 140 return (u.dblu_d); 141 } else { 142 /* 143 * The result is normal; just replace the old exponent with the 144 * new one. 145 */ 146 u.dblu_dbl.dbl_exp = newexp; 147 return (u.dblu_d); 148 } 149 } 150