osprey/libm/mips/expf.c

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/*
 * Copyright 2003, 2004, 2005, 2006 PathScale, Inc.  All Rights Reserved.
 */


/*

  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

*/

/* ====================================================================
 * ====================================================================
 *
 * Module: expf.c
 * $Revision: 1.5 $
 * $Date: 04/12/21 14:58:21-08:00 $
 * $Author: bos@eng-25.internal.keyresearch.com $
 * $Source: /home/bos/bk/kpro64-pending/libm/mips/SCCS/s.expf.c $
 *
 * Revision history:
 *  09-Jun-93 - Original Version
 *
 * Description: source code for expf function
 *
 * ====================================================================
 * ====================================================================
 */

static char *rcs_id = "$Source: /home/bos/bk/kpro64-pending/libm/mips/SCCS/s.expf.c $ $Revision: 1.5 $";

#ifdef _CALL_MATHERR
#include <stdio.h>
#include <math.h>
#include <errno.h>
#endif

#include "libm.h"

/*  Algorithm adapted from
  "Table-driven Implementation of the Exponential Function in
  IEEE Floating Point Arithmetic", Peter Tang, ACM Transactions on
  Mathematical Software, Vol. 15, No. 2, June 1989
 */

#if defined(mips) && !defined(__GNUC__)
extern  float fexp(float);
extern  float expf(float);

#pragma weak fexp = __expf
#pragma weak expf = __expf
#endif

#if defined(BUILD_OS_DARWIN) /* Mach-O doesn't support aliases */
extern float __expf(float);
#pragma weak expf
float expf( float x ) {
  return __expf( x );
}
#elif defined(__GNUC__)
extern  float  __expf(float);
float    expf(float) __attribute__ ((weak, alias ("__expf")));
#endif

extern  const du  _expftab[];

/* coefficients for polynomial approximation of exp on +/- log(2)/64    */

static const du P[] =
{
{D(0x3ff00000, 0x00000000)},
{D(0x3ff00000, 0x00000000)},
{D(0x3fe00008, 0x745da559)},
{D(0x3fc55569, 0x9fd0029e)},
};

static const du rln2by32 =
{D(0x40471547, 0x652b82fe)};

static const du ln2by32hi =
{D(0x3f962e42, 0xfef00000)};

static const du ln2by32lo =
{D(0x3d8473de, 0x6af278ed)};

static const  fu  Qnan = {QNANF};

static const fu Inf = {0x7f800000};

static const fu f_one = {0x3f800000};

static const fu Ulimit = {0x42b17217};

static const fu Llimit = {0xc2cff1b4};


/* ====================================================================
 *
 * FunctionName   expf
 *
 * Description    computes exponential function of arg
 *
 * ====================================================================
 */

float
__expf( float x )
{
#ifdef _32BIT_MACHINE

int l;

#else

long long l;

#endif

int ix, xp, j, m, n;
double  twopm;
double  result, nd, y;
double  s;
double  dx;
double  poly;
#ifdef _CALL_MATHERR
struct exception  exstruct;
#endif

  /* extract exponent of x for some quick screening */

  FLT2INT(x, ix);   /* copy arg to an integer */
  xp = (ix >> MANTWIDTH);
  xp &= 0xff;

  if ( xp < 0x85 )
  {
    /* |x| < 64.0 */

    if ( xp >= 0x66 )
    {
      /* |x| >= 2^-25 */
L:
      dx = x;

      /* reduce x to +/- log(2)/64    */

      nd = dx*rln2by32.d;
      n = ROUND(nd);
      nd = n;

      y = x - nd*ln2by32hi.d - nd*ln2by32lo.d;

      j = n & 0x1f;
      m = n >> 5;

      s = _expftab[j].d;

      poly = (P[3].d*y + P[2].d)*(y*y) + y;

      l = m + DEXPBIAS;
      l <<= DMANTWIDTH;

#ifdef _32BIT_MACHINE

      twopm = 0.0;
      INT2DBLHI(l, twopm);
#else
      LL2DBL(l, twopm);
#endif
      result = s + s*poly;
      result *= twopm;

      return ( (float)result );
    }

    return ( f_one.f + x );
  }

  if ( x != x )
  {
    /* x is a NaN; return a quiet NaN */

#ifdef _CALL_MATHERR

                exstruct.type = DOMAIN;
                exstruct.name = "expf";
                exstruct.arg1 = x;
                exstruct.retval = Qnan.f;

                if ( matherr( &exstruct ) == 0 )
                {
                        fprintf(stderr, "domain error in expf\n");
                        SETERRNO(EDOM);
                }

                return ( exstruct.retval );
#else
    NAN_SETERRNO(EDOM);
    
    return ( Qnan.f );
#endif
  }

  if ( x > Ulimit.f )
  {
#ifdef _CALL_MATHERR

                exstruct.type = OVERFLOW;
                exstruct.name = "expf";
                exstruct.arg1 = x;
                exstruct.retval = Inf.f;

                if ( matherr( &exstruct ) == 0 )
                {
                        fprintf(stderr, "overflow error in expf\n");
                        SETERRNO(ERANGE);
                }

                return ( exstruct.retval );
#else
    SETERRNO(ERANGE);

    return ( Inf.f );
#endif
  }

  if ( x < Llimit.f )
  {
#ifdef _CALL_MATHERR

                exstruct.type = UNDERFLOW;
                exstruct.name = "expf";
                exstruct.arg1 = x;
                exstruct.retval = 0.0;

                if ( matherr( &exstruct ) == 0 )
                {
                        fprintf(stderr, "underflow error in expf\n");
                        SETERRNO(ERANGE);
                }

                return ( exstruct.retval );
#else
    SETERRNO(ERANGE);

    return ( 0.0f );
#endif
  }

  goto L;
}

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