1 /* $NetBSD: compat_modf_ieee754.c,v 1.1 2006/06/27 18:16:47 drochner Exp $ */ 2 3 /* 4 * Copyright (c) 1994, 1995 Carnegie-Mellon University. 5 * All rights reserved. 6 * 7 * Author: Chris G. Demetriou 8 * 9 * Permission to use, copy, modify and distribute this software and 10 * its documentation is hereby granted, provided that both the copyright 11 * notice and this permission notice appear in all copies of the 12 * software, derivative works or modified versions, and any portions 13 * thereof, and that both notices appear in supporting documentation. 14 * 15 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" 16 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND 17 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. 18 * 19 * Carnegie Mellon requests users of this software to return to 20 * 21 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU 22 * School of Computer Science 23 * Carnegie Mellon University 24 * Pittsburgh PA 15213-3890 25 * 26 * any improvements or extensions that they make and grant Carnegie the 27 * rights to redistribute these changes. 28 */ 29 30 #include <sys/types.h> 31 #include <machine/ieee.h> 32 #include <errno.h> 33 #include <math.h> 34 35 /* 36 * double modf(double val, double *iptr) 37 * returns: f and i such that |f| < 1.0, (f + i) = val, and 38 * sign(f) == sign(i) == sign(val). 39 * 40 * Beware signedness when doing subtraction, and also operand size! 41 */ 42 double 43 modf(double val, double *iptr) 44 { 45 union ieee_double_u u, v; 46 u_int64_t frac; 47 48 /* 49 * If input is Inf or NaN, return it and leave i alone. 50 */ 51 u.dblu_d = val; 52 if (u.dblu_dbl.dbl_exp == DBL_EXP_INFNAN) 53 return (u.dblu_d); 54 55 /* 56 * If input can't have a fractional part, return 57 * (appropriately signed) zero, and make i be the input. 58 */ 59 if ((int)u.dblu_dbl.dbl_exp - DBL_EXP_BIAS > DBL_FRACBITS - 1) { 60 *iptr = u.dblu_d; 61 v.dblu_d = 0.0; 62 v.dblu_dbl.dbl_sign = u.dblu_dbl.dbl_sign; 63 return (v.dblu_d); 64 } 65 66 /* 67 * If |input| < 1.0, return it, and set i to the appropriately 68 * signed zero. 69 */ 70 if (u.dblu_dbl.dbl_exp < DBL_EXP_BIAS) { 71 v.dblu_d = 0.0; 72 v.dblu_dbl.dbl_sign = u.dblu_dbl.dbl_sign; 73 *iptr = v.dblu_d; 74 return (u.dblu_d); 75 } 76 77 /* 78 * There can be a fractional part of the input. 79 * If you look at the math involved for a few seconds, it's 80 * plain to see that the integral part is the input, with the 81 * low (DBL_FRACBITS - (exponent - DBL_EXP_BIAS)) bits zeroed, 82 * the fractional part is the part with the rest of the 83 * bits zeroed. Just zeroing the high bits to get the 84 * fractional part would yield a fraction in need of 85 * normalization. Therefore, we take the easy way out, and 86 * just use subtraction to get the fractional part. 87 */ 88 v.dblu_d = u.dblu_d; 89 /* Zero the low bits of the fraction, the sleazy way. */ 90 frac = ((u_int64_t)v.dblu_dbl.dbl_frach << 32) + v.dblu_dbl.dbl_fracl; 91 frac >>= DBL_FRACBITS - (u.dblu_dbl.dbl_exp - DBL_EXP_BIAS); 92 frac <<= DBL_FRACBITS - (u.dblu_dbl.dbl_exp - DBL_EXP_BIAS); 93 v.dblu_dbl.dbl_fracl = (unsigned int)frac & 0xffffffff; 94 v.dblu_dbl.dbl_frach = (unsigned int)(frac >> 32); 95 *iptr = v.dblu_d; 96 97 u.dblu_d -= v.dblu_d; 98 u.dblu_dbl.dbl_sign = v.dblu_dbl.dbl_sign; 99 return (u.dblu_d); 100 } 101