5980be9b3c
This work is based in part on code from NetBSD libm, libc and kernel. The library is partly public domain and partly BSD-style licensed.
104 lines
3.1 KiB
C
104 lines
3.1 KiB
C
/* $NetBSD: modf_ieee754.c,v 1.3 2010/01/27 14:10:41 drochner Exp $ */
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/*
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* Copyright (c) 1994, 1995 Carnegie-Mellon University.
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* All rights reserved.
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*
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* Author: Chris G. Demetriou
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*
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* Permission to use, copy, modify and distribute this software and
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* its documentation is hereby granted, provided that both the copyright
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* notice and this permission notice appear in all copies of the
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* software, derivative works or modified versions, and any portions
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* thereof, and that both notices appear in supporting documentation.
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*
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* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
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* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
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* FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
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*
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* Carnegie Mellon requests users of this software to return to
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*
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* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
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* School of Computer Science
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* Carnegie Mellon University
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* Pittsburgh PA 15213-3890
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*
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* any improvements or extensions that they make and grant Carnegie the
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* rights to redistribute these changes.
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*/
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#include <sys/types.h>
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#include <machine/ieee.h>
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#include <errno.h>
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#include <math.h>
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#include <stdint.h>
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/*
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* double modf(double val, double *iptr)
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* returns: f and i such that |f| < 1.0, (f + i) = val, and
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* sign(f) == sign(i) == sign(val).
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*
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* Beware signedness when doing subtraction, and also operand size!
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*/
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double
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modf(double val, double *iptr)
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{
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union ieee_double_u u, v;
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uint64_t frac;
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/*
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* If input is +/-Inf or NaN, return +/-0 or NaN.
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*/
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u.dblu_d = val;
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if (u.dblu_dbl.dbl_exp == DBL_EXP_INFNAN) {
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*iptr = u.dblu_d;
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return (0.0 / u.dblu_d);
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}
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/*
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* If input can't have a fractional part, return
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* (appropriately signed) zero, and make i be the input.
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*/
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if ((int)u.dblu_dbl.dbl_exp - DBL_EXP_BIAS > DBL_FRACBITS - 1) {
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*iptr = u.dblu_d;
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v.dblu_d = 0.0;
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v.dblu_dbl.dbl_sign = u.dblu_dbl.dbl_sign;
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return (v.dblu_d);
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}
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/*
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* If |input| < 1.0, return it, and set i to the appropriately
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* signed zero.
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*/
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if (u.dblu_dbl.dbl_exp < DBL_EXP_BIAS) {
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v.dblu_d = 0.0;
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v.dblu_dbl.dbl_sign = u.dblu_dbl.dbl_sign;
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*iptr = v.dblu_d;
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return (u.dblu_d);
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}
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/*
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* There can be a fractional part of the input.
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* If you look at the math involved for a few seconds, it's
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* plain to see that the integral part is the input, with the
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* low (DBL_FRACBITS - (exponent - DBL_EXP_BIAS)) bits zeroed,
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* the fractional part is the part with the rest of the
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* bits zeroed. Just zeroing the high bits to get the
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* fractional part would yield a fraction in need of
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* normalization. Therefore, we take the easy way out, and
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* just use subtraction to get the fractional part.
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*/
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v.dblu_d = u.dblu_d;
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/* Zero the low bits of the fraction, the sleazy way. */
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frac = ((uint64_t)v.dblu_dbl.dbl_frach << 32) + v.dblu_dbl.dbl_fracl;
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frac >>= DBL_FRACBITS - (u.dblu_dbl.dbl_exp - DBL_EXP_BIAS);
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frac <<= DBL_FRACBITS - (u.dblu_dbl.dbl_exp - DBL_EXP_BIAS);
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v.dblu_dbl.dbl_fracl = frac & 0xffffffff;
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v.dblu_dbl.dbl_frach = frac >> 32;
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*iptr = v.dblu_d;
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u.dblu_d -= v.dblu_d;
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u.dblu_dbl.dbl_sign = v.dblu_dbl.dbl_sign;
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return (u.dblu_d);
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}
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