1 /* $NetBSD: compat_ldexp_ieee754.c,v 1.5 2010/04/23 19:04:54 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 * 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 #if defined(LIBC_SCCS) && !defined(lint) 34 __RCSID("$NetBSD: compat_ldexp_ieee754.c,v 1.5 2010/04/23 19:04:54 drochner Exp $"); 35 #endif /* LIBC_SCCS and not lint */ 36 37 #include <sys/types.h> 38 #include <machine/ieee.h> 39 #include <errno.h> 40 41 double ldexp(double, int); 42 43 /* 44 * Multiply the given value by 2^expon. 45 */ 46 double 47 ldexp(double val, int expon) 48 { 49 int oldexp, newexp; 50 union ieee_double_u u, mul; 51 52 u.dblu_d = val; 53 oldexp = u.dblu_dbl.dbl_exp; 54 55 /* 56 * If input is zero, Inf or NaN, just return it. 57 */ 58 if (u.dblu_d == 0.0 || oldexp == DBL_EXP_INFNAN) 59 return (val); 60 61 if (oldexp == 0) { 62 /* 63 * u.v is denormal. We must adjust it so that the exponent 64 * arithmetic below will work. 65 */ 66 if (expon <= DBL_EXP_BIAS) { 67 /* 68 * Optimization: if the scaling can be done in a single 69 * multiply, or underflows, just do it now. 70 */ 71 if (expon <= -DBL_FRACBITS) { 72 errno = ERANGE; 73 return (val < 0.0 ? -0.0 : 0.0); 74 } 75 mul.dblu_d = 0.0; 76 mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS; 77 u.dblu_d *= mul.dblu_d; 78 if (u.dblu_d == 0.0) { 79 errno = ERANGE; 80 return (val < 0.0 ? -0.0 : 0.0); 81 } 82 return (u.dblu_d); 83 } else { 84 /* 85 * We know that expon is very large, and therefore the 86 * result cannot be denormal (though it may be Inf). 87 * Shift u.v by just enough to make it normal. 88 */ 89 mul.dblu_d = 0.0; 90 mul.dblu_dbl.dbl_exp = DBL_FRACBITS + DBL_EXP_BIAS; 91 u.dblu_d *= mul.dblu_d; 92 expon -= DBL_FRACBITS; 93 oldexp = u.dblu_dbl.dbl_exp; 94 } 95 } 96 97 /* 98 * u.v is now normalized and oldexp has been adjusted if necessary. 99 * Calculate the new exponent and check for underflow and overflow. 100 */ 101 newexp = oldexp + expon; 102 103 if (newexp <= 0) { 104 /* 105 * The output number is either denormal or underflows (see 106 * comments in machine/ieee.h). 107 */ 108 if (newexp <= -DBL_FRACBITS) { 109 errno = ERANGE; 110 return (val < 0.0 ? -0.0 : 0.0); 111 } 112 /* 113 * Denormalize the result. We do this with a multiply. If 114 * expon is very large, it won't fit in a double, so we have 115 * to adjust the exponent first. This is safe because we know 116 * that u.v is normal at this point. 117 */ 118 if (expon <= -DBL_EXP_BIAS) { 119 u.dblu_dbl.dbl_exp = 1; 120 expon += oldexp - 1; 121 } 122 mul.dblu_d = 0.0; 123 mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS; 124 u.dblu_d *= mul.dblu_d; 125 return (u.dblu_d); 126 } else if (newexp >= DBL_EXP_INFNAN) { 127 /* 128 * The result overflowed; return +/-Inf. 129 */ 130 u.dblu_dbl.dbl_exp = DBL_EXP_INFNAN; 131 u.dblu_dbl.dbl_frach = 0; 132 u.dblu_dbl.dbl_fracl = 0; 133 errno = ERANGE; 134 return (u.dblu_d); 135 } else { 136 /* 137 * The result is normal; just replace the old exponent with the 138 * new one. 139 */ 140 u.dblu_dbl.dbl_exp = newexp; 141 return (u.dblu_d); 142 } 143 } 144