1 /* $NetBSD: ldexp_ieee754.c,v 1.5 2008/04/28 20:22:59 martin 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: ldexp_ieee754.c,v 1.5 2008/04/28 20:22:59 martin Exp $"); 35 #endif /* LIBC_SCCS and not lint */ 36 37 #include <sys/types.h> 38 #include <machine/ieee.h> 39 #include <errno.h> 40 #include <math.h> 41 42 /* 43 * Multiply the given value by 2^expon. 44 */ 45 double 46 ldexp(double val, int expon) 47 { 48 int oldexp, newexp; 49 union ieee_double_u u, mul; 50 51 u.dblu_d = val; 52 oldexp = u.dblu_dbl.dbl_exp; 53 54 /* 55 * If input is zero, Inf or NaN, just return it. 56 */ 57 if (u.dblu_d == 0.0 || oldexp == DBL_EXP_INFNAN) 58 return (val); 59 60 if (oldexp == 0) { 61 /* 62 * u.v is denormal. We must adjust it so that the exponent 63 * arithmetic below will work. 64 */ 65 if (expon <= DBL_EXP_BIAS) { 66 /* 67 * Optimization: if the scaling can be done in a single 68 * multiply, or underflows, just do it now. 69 */ 70 if (expon <= -DBL_FRACBITS) { 71 errno = ERANGE; 72 return (val < 0.0 ? -0.0 : 0.0); 73 } 74 mul.dblu_d = 0.0; 75 mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS; 76 u.dblu_d *= mul.dblu_d; 77 if (u.dblu_d == 0.0) { 78 errno = ERANGE; 79 return (val < 0.0 ? -0.0 : 0.0); 80 } 81 return (u.dblu_d); 82 } else { 83 /* 84 * We know that expon is very large, and therefore the 85 * result cannot be denormal (though it may be Inf). 86 * Shift u.v by just enough to make it normal. 87 */ 88 mul.dblu_d = 0.0; 89 mul.dblu_dbl.dbl_exp = DBL_FRACBITS + DBL_EXP_BIAS; 90 u.dblu_d *= mul.dblu_d; 91 expon -= DBL_FRACBITS; 92 oldexp = u.dblu_dbl.dbl_exp; 93 } 94 } 95 96 /* 97 * u.v is now normalized and oldexp has been adjusted if necessary. 98 * Calculate the new exponent and check for underflow and overflow. 99 */ 100 newexp = oldexp + expon; 101 102 if (newexp <= 0) { 103 /* 104 * The output number is either denormal or underflows (see 105 * comments in machine/ieee.h). 106 */ 107 if (newexp <= -DBL_FRACBITS) { 108 errno = ERANGE; 109 return (val < 0.0 ? -0.0 : 0.0); 110 } 111 /* 112 * Denormalize the result. We do this with a multiply. If 113 * expon is very large, it won't fit in a double, so we have 114 * to adjust the exponent first. This is safe because we know 115 * that u.v is normal at this point. 116 */ 117 if (expon <= -DBL_EXP_BIAS) { 118 u.dblu_dbl.dbl_exp = 1; 119 expon += oldexp - 1; 120 } 121 mul.dblu_d = 0.0; 122 mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS; 123 u.dblu_d *= mul.dblu_d; 124 return (u.dblu_d); 125 } else if (newexp >= DBL_EXP_INFNAN) { 126 /* 127 * The result overflowed; return +/-Inf. 128 */ 129 u.dblu_dbl.dbl_exp = DBL_EXP_INFNAN; 130 u.dblu_dbl.dbl_frach = 0; 131 u.dblu_dbl.dbl_fracl = 0; 132 errno = ERANGE; 133 return (u.dblu_d); 134 } else { 135 /* 136 * The result is normal; just replace the old exponent with the 137 * new one. 138 */ 139 u.dblu_dbl.dbl_exp = newexp; 140 return (u.dblu_d); 141 } 142 } 143