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