1 /* $NetBSD: compat_ldexp_ieee754.c,v 1.4 2008/09/28 18:54:30 christos 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 #ifdef USE_LIBM 33 #include "s_finite.c" 34 #include "s_scalbn.c" 35 #include "s_ldexp.c" 36 #else 37 #include <sys/cdefs.h> 38 #if defined(LIBC_SCCS) && !defined(lint) 39 __RCSID("$NetBSD: compat_ldexp_ieee754.c,v 1.4 2008/09/28 18:54:30 christos Exp $"); 40 #endif /* LIBC_SCCS and not lint */ 41 42 #include <sys/types.h> 43 #include <machine/ieee.h> 44 #include <errno.h> 45 #include <math.h> 46 47 /* 48 * Multiply the given value by 2^expon. 49 */ 50 double 51 ldexp(double val, int expon) 52 { 53 int oldexp, newexp; 54 union ieee_double_u u, mul; 55 56 u.dblu_d = val; 57 oldexp = u.dblu_dbl.dbl_exp; 58 59 /* 60 * If input is zero, Inf or NaN, just return it. 61 */ 62 if (u.dblu_d == 0.0 || oldexp == DBL_EXP_INFNAN) 63 return (val); 64 65 if (oldexp == 0) { 66 /* 67 * u.v is denormal. We must adjust it so that the exponent 68 * arithmetic below will work. 69 */ 70 if (expon <= DBL_EXP_BIAS) { 71 /* 72 * Optimization: if the scaling can be done in a single 73 * multiply, or underflows, just do it now. 74 */ 75 if (expon <= -DBL_FRACBITS) { 76 errno = ERANGE; 77 return (val < 0.0 ? -0.0 : 0.0); 78 } 79 mul.dblu_d = 0.0; 80 mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS; 81 u.dblu_d *= mul.dblu_d; 82 if (u.dblu_d == 0.0) { 83 errno = ERANGE; 84 return (val < 0.0 ? -0.0 : 0.0); 85 } 86 return (u.dblu_d); 87 } else { 88 /* 89 * We know that expon is very large, and therefore the 90 * result cannot be denormal (though it may be Inf). 91 * Shift u.v by just enough to make it normal. 92 */ 93 mul.dblu_d = 0.0; 94 mul.dblu_dbl.dbl_exp = DBL_FRACBITS + DBL_EXP_BIAS; 95 u.dblu_d *= mul.dblu_d; 96 expon -= DBL_FRACBITS; 97 oldexp = u.dblu_dbl.dbl_exp; 98 } 99 } 100 101 /* 102 * u.v is now normalized and oldexp has been adjusted if necessary. 103 * Calculate the new exponent and check for underflow and overflow. 104 */ 105 newexp = oldexp + expon; 106 107 if (newexp <= 0) { 108 /* 109 * The output number is either denormal or underflows (see 110 * comments in machine/ieee.h). 111 */ 112 if (newexp <= -DBL_FRACBITS) { 113 errno = ERANGE; 114 return (val < 0.0 ? -0.0 : 0.0); 115 } 116 /* 117 * Denormalize the result. We do this with a multiply. If 118 * expon is very large, it won't fit in a double, so we have 119 * to adjust the exponent first. This is safe because we know 120 * that u.v is normal at this point. 121 */ 122 if (expon <= -DBL_EXP_BIAS) { 123 u.dblu_dbl.dbl_exp = 1; 124 expon += oldexp - 1; 125 } 126 mul.dblu_d = 0.0; 127 mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS; 128 u.dblu_d *= mul.dblu_d; 129 return (u.dblu_d); 130 } else if (newexp >= DBL_EXP_INFNAN) { 131 /* 132 * The result overflowed; return +/-Inf. 133 */ 134 u.dblu_dbl.dbl_exp = DBL_EXP_INFNAN; 135 u.dblu_dbl.dbl_frach = 0; 136 u.dblu_dbl.dbl_fracl = 0; 137 errno = ERANGE; 138 return (u.dblu_d); 139 } else { 140 /* 141 * The result is normal; just replace the old exponent with the 142 * new one. 143 */ 144 u.dblu_dbl.dbl_exp = newexp; 145 return (u.dblu_d); 146 } 147 } 148 #endif 149