1 /* $OpenBSD: modf.c,v 1.7 2023/08/13 06:55:37 miod Exp $ */ 2 /* $NetBSD: modf.c,v 1.1 1995/02/10 17:50:25 cgd Exp $ */ 3 4 /* 5 * Copyright (c) 1994, 1995 Carnegie-Mellon University. 6 * All rights reserved. 7 * 8 * Author: Chris G. Demetriou 9 * 10 * Permission to use, copy, modify and distribute this software and 11 * its documentation is hereby granted, provided that both the copyright 12 * notice and this permission notice appear in all copies of the 13 * software, derivative works or modified versions, and any portions 14 * thereof, and that both notices appear in supporting documentation. 15 * 16 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" 17 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND 18 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. 19 * 20 * Carnegie Mellon requests users of this software to return to 21 * 22 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU 23 * School of Computer Science 24 * Carnegie Mellon University 25 * Pittsburgh PA 15213-3890 26 * 27 * any improvements or extensions that they make and grant Carnegie the 28 * rights to redistribute these changes. 29 */ 30 31 #include <sys/types.h> 32 #include <machine/ieee.h> 33 #include <errno.h> 34 #include <float.h> 35 #include <math.h> 36 37 /* 38 * double modf(double val, double *iptr) 39 * returns: f and i such that |f| < 1.0, (f + i) = val, and 40 * sign(f) == sign(i) == sign(val). 41 * 42 * Beware signedness when doing subtraction, and also operand size! 43 */ 44 double 45 modf(double val, double *iptr) 46 { 47 union doub { 48 double v; 49 struct ieee_double s; 50 } u, v; 51 u_int64_t frac; 52 53 /* 54 * If input is +/-Inf or NaN, return +/-0 or NaN. 55 */ 56 u.v = val; 57 if (u.s.dbl_exp == DBL_EXP_INFNAN) { 58 *iptr = u.v; 59 return (0.0 / u.v); 60 } 61 62 /* 63 * If input can't have a fractional part, return 64 * (appropriately signed) zero, and make i be the input. 65 */ 66 if ((int)u.s.dbl_exp - DBL_EXP_BIAS > DBL_FRACBITS - 1) { 67 *iptr = u.v; 68 v.v = 0.0; 69 v.s.dbl_sign = u.s.dbl_sign; 70 return (v.v); 71 } 72 73 /* 74 * If |input| < 1.0, return it, and set i to the appropriately 75 * signed zero. 76 */ 77 if (u.s.dbl_exp < DBL_EXP_BIAS) { 78 v.v = 0.0; 79 v.s.dbl_sign = u.s.dbl_sign; 80 *iptr = v.v; 81 return (u.v); 82 } 83 84 /* 85 * There can be a fractional part of the input. 86 * If you look at the math involved for a few seconds, it's 87 * plain to see that the integral part is the input, with the 88 * low (DBL_FRACBITS - (exponent - DBL_EXP_BIAS)) bits zeroed, 89 * the fractional part is the part with the rest of the 90 * bits zeroed. Just zeroing the high bits to get the 91 * fractional part would yield a fraction in need of 92 * normalization. Therefore, we take the easy way out, and 93 * just use subtraction to get the fractional part. 94 */ 95 v.v = u.v; 96 /* Zero the low bits of the fraction, the sleazy way. */ 97 frac = ((u_int64_t)v.s.dbl_frach << 32) + v.s.dbl_fracl; 98 frac >>= DBL_FRACBITS - (u.s.dbl_exp - DBL_EXP_BIAS); 99 frac <<= DBL_FRACBITS - (u.s.dbl_exp - DBL_EXP_BIAS); 100 v.s.dbl_fracl = frac & 0xffffffff; 101 v.s.dbl_frach = frac >> 32; 102 *iptr = v.v; 103 104 u.v -= v.v; 105 u.s.dbl_sign = v.s.dbl_sign; 106 return (u.v); 107 } 108 109 #if LDBL_MANT_DIG == DBL_MANT_DIG 110 __strong_alias(modfl, modf); 111 #endif /* LDBL_MANT_DIG == DBL_MANT_DIG */ 112