osprey/libm/mips/log1pf.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: log1pf.c
 * $Revision: 1.5 $
 * $Date: 04/12/21 14:58:22-08:00 $
 * $Author: bos@eng-25.internal.keyresearch.com $
 * $Source: /home/bos/bk/kpro64-pending/libm/mips/SCCS/s.log1pf.c $
 *
 * Revision history:
 *  09-Jun-93 - Original Version
 *
 * Description: source code for log1pf function
 *
 * ====================================================================
 * ====================================================================
 */

static char *rcs_id = "$Source: /home/bos/bk/kpro64-pending/libm/mips/SCCS/s.log1pf.c $ $Revision: 1.5 $";

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

#include "libm.h"

/*  Algorithm from
  "Table-Driven Implementation of the Logarithm Function in IEEE
  Floating-Point Arithmetic", Peter Tang, Argonne National Laboratory,
  ACM Transactions on Mathematical Software, Vol. 16, No. 4,
  Dec. 1990
*/

#if defined(mips) && !defined(__GNUC__)
extern  float flog1p(float);
extern  float log1pf(float);

#pragma weak flog1p = __log1pf
#pragma weak log1pf = __log1pf
#endif

#if defined(BUILD_OS_DARWIN) /* Mach-O doesn't support aliases */
extern float __log1pf(float);
#pragma weak log1pf
float log1pf( float x ) {
  return __log1pf( x );
}
#elif defined(__GNUC__)
extern  float  __log1pf(float);
float    log1pf(float) __attribute__ ((weak, alias ("__log1pf")));
#endif

extern  const fu  _logftabhi[];
extern  const fu  _logftablo[];

static const  fu  Qnan = {QNANF};

static const fu Neginf = {0x7f800000};

static const fu Inf = {0x7f800000};

static const fu P[] =
{
{0x3f800000},
{0x3daaaaa9},
{0x3c4dffbb},
};

static const fu Q[] =
{
{0x3f800000},
{0x3daaaac2},
};

static const fu f_m_one = {0xbf800000};

static const fu f_one = {0x3f800000};

/*  exp(-1/16) - 1   */

static const fu T1 = {0xbd782a03};

/*  exp(1/16) - 1   */

static const fu T2 = {0x3d8415ac};

static const fu T3 = {0x4c800000};

static const fu twop7 = {0x43000000};

static const fu twopm7 = {0x3c000000};

static const fu log2_lead = {0x3f317200};

static const fu log2_trail = {0x35bfbe8e};


/* ====================================================================
 *
 * FunctionName   log1pf
 *
 * Description    computes log1p function of arg
 *
 * ====================================================================
 */

float
__log1pf( float x )
{
int xpt;
float u, v;
double  u1;
float q;
float result;
int m, n;
float y, f, F;
float l_lead, l_trail;
int j, k;
float twopnegm;
float md;
#ifdef _CALL_MATHERR
struct exception  exstruct;
#endif

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

#ifdef _CALL_MATHERR

                exstruct.type = DOMAIN;
                exstruct.name = "log1pf";
                exstruct.arg1 = x;
                exstruct.retval = Qnan.f;

                if ( matherr( &exstruct ) == 0 )
                {
                        fprintf(stderr, "domain error in log1pf\n");
                        SETERRNO(EDOM);
                }

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

  if ( (T1.f < x) && (x < T2.f) )
  {
    /*  exp(-1/16) < 1 + x < exp(1/16)  */

    FLT2INT(x, xpt);  /* copy arg to an integer */
    xpt >>= MANTWIDTH;  /* shift off mantissa */
    xpt &= 0xff;

    if ( xpt >= 0x67 )
    {
      /* |x| >= 2^(-24) */

      u1 = x/(2.0 + x);
      u1 = u1 + u1;
      u = u1;
      v = u1*u1;

      q = (P[2].f*v + P[1].f)*(v*u);

      result = u1 + q;

      return ( result );
    }

    return ( x );
  }

  else if ( (x > f_m_one.f) && (x != Inf.f) )
  {
    if ( x >= T3.f )
      y = x;
    else
      y = f_one.f + x;

    FLT2INT(y, k);  /* copy y to an integer */
    m = (k >> MANTWIDTH); /* shift off mantissa */
    m -= EXPBIAS;
    k &= 0x7fffff;
    k |= 0x3f800000;
    INT2FLT(k, y);

    u = twop7.f*y;

    j = ROUNDF(u);

    F = j;
    j -= 128;
  
    F = twopm7.f*F;

    if ( m <= -2 )
      f = y - F;
    else 
    {
      n = EXPBIAS - m;
      n <<= MANTWIDTH;

      INT2FLT(n, twopnegm); /* build 2^(-m) */

      if ( m <= 23 )
        f = (twopnegm - F) + twopnegm*x;
      else if ( m <= 50 )
        f = (twopnegm*x - F) + twopnegm;
      else
        f = y - F;
    }

    md = m;

    l_lead = md*log2_lead.f;
    l_trail = md*log2_trail.f;

    u = (f + f)/(y + F);

    l_lead += _logftabhi[j].f;
    l_trail += _logftablo[j].f;

    v = u*u;

    q = Q[1].f*(v*u);

    result = l_lead + (u + (q + l_trail));

    return ( result );
  }

  if ( x == Inf.f )
  {
    return ( Inf.f );
  }

  if ( x == f_m_one.f )
  {
#ifdef _CALL_MATHERR

                exstruct.type = OVERFLOW;
                exstruct.name = "log1pf";
                exstruct.arg1 = x;
                exstruct.retval = Neginf.f;

                if ( matherr( &exstruct ) == 0 )
                {
                        fprintf(stderr, "overflow range error in log1pf\n");
                        SETERRNO(ERANGE);
                }

                return ( exstruct.retval );
#else

    SETERRNO(ERANGE);

    return ( Neginf.f );
#endif
  }

  /*  x < -1.0 */

#ifdef _CALL_MATHERR

        exstruct.type = DOMAIN;
        exstruct.name = "log1pf";
        exstruct.arg1 = x;
        exstruct.retval = Qnan.f;

        if ( matherr( &exstruct ) == 0 )
        {
                fprintf(stderr, "domain error in log1pf\n");
                SETERRNO(EDOM);
        }

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

  return ( Qnan.f );
#endif
}

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