osprey/libm/mips/extra/trunc.c

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/*

  Copyright (C) 2000, 2001 Silicon Graphics, Inc.  All Rights Reserved.

  This program is free software; you can redistribute it and/or modify it
  under the terms of version 2.1 of the GNU Lesser General Public License 
  as published by the Free Software Foundation.

  This program is distributed in the hope that it would be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  

  Further, this software is distributed without any warranty that it is
  free of the rightful claim of any third person regarding infringement 
  or the like.  Any license provided herein, whether implied or 
  otherwise, applies only to this software file.  Patent licenses, if
  any, provided herein do not apply to combinations of this program with 
  other software, or any other product whatsoever.  

  You should have received a copy of the GNU Lesser General Public 
  License along with this program; if not, write the Free Software 
  Foundation, Inc., 59 Temple Place - Suite 330, Boston MA 02111-1307, 
  USA.

  Contact information:  Silicon Graphics, Inc., 1600 Amphitheatre Pky,
  Mountain View, CA 94043, or:

  http://www.sgi.com

  For further information regarding this notice, see:

  http://oss.sgi.com/projects/GenInfo/NoticeExplan

*/

#include <errno.h>

extern  int errno;

typedef union
{
  long long lword;
        double  d;
} du;

static const du Quiet_nan = 
{
0x7ff8000000000000ll,
};

extern  double  fabs(double);

#ifdef mips
extern  double  trunc(double);

#pragma weak trunc = __trunc
#endif

#if defined(BUILD_OS_DARWIN) /* Mach-O doesn't support aliases */
extern double __trunc(double);
#pragma weak trunc
double trunc( double arg ) {
  return __trunc( arg );
}
#elif defined(__GNUC__)
extern  double  __trunc(double);
double    trunc() __attribute__ ((weak, alias ("__trunc")));
#endif

#define DMANTWIDTH  52
#define DEXPWIDTH 11
#define DSIGNMASK 0x7fffffffffffffffll
#define DEXPMASK  0x800fffffffffffffll
#define DQNANBITMASK  0xfff7ffffffffffffll

#define MANTWIDTH 23
#define EXPWIDTH  8
#define SIGNMASK  0x7fffffff
#define EXPMASK   0x807fffff
#define QNANBITMASK 0xffbfffff

double
__trunc( double arg )
{
unsigned long long  ll, exp, mantissa;
int sign;
int shift_count;
double  result;


  ll = *(unsigned long long *)&arg;

  exp = (ll >> DMANTWIDTH);
  sign = (exp >> DEXPWIDTH);
  exp &= 0x7ff;
  mantissa = (ll & (DSIGNMASK & DEXPMASK));

  if ( exp == 0x7ff )
  {
    /* arg is an infinity, or a NaN */

    if ( mantissa == 0 )
      return ( arg );
    else 
    {
      errno = EDOM;
      return ( Quiet_nan.d );
    }
  }

  if ( exp >= 0x433 )
    return ( arg );

  if ( fabs(arg) < 1.0 )
    return ( (sign == 0) ? 0.0 : -0.0 );

  shift_count = 0x433 - exp;

  ll >>= shift_count;
  ll <<= shift_count;

  *(long long *)&result = ll;

  return ( result );
}

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