osprey/libm/mips/logf.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: logf.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.logf.c $
 *
 * Revision history:
 *  09-Jun-93 - Original Version
 *
 * Description: source code for logf function
 *
 * ====================================================================
 * ====================================================================
 */

static char *rcs_id = "$Source: /home/bos/bk/kpro64-pending/libm/mips/SCCS/s.logf.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 flog(float);
extern  float logf(float);

#pragma weak flog = __logf
#pragma weak logf = __logf
#endif

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

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

static const  fu  Qnan = {QNANF};

static const fu Neginf = {0xff800000};

static const fu Inf = {0x7f800000};

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

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

static const fu log2_lead = {0x3f317200};

static const fu log2_trail = {0x35bfbe8e};

static const fu f_one = {0x3f800000};

static const fu Scaleup = {0x4b000000};

/* exp(-1/16) */

static const int lim1 = {0x3f707d5f};

/* exp(1/16) */

static const int lim2 = {0x3f88415b};

static const int one = {0x3f800000};


/* ====================================================================
 *
 * FunctionName   logf
 *
 * Description    computes natural logarithm of arg
 *
 * ====================================================================
 */

float
__logf( float x )
{
int ix;
int j, m;
float u, v;
float result;
float f, F;
float l_lead, l_trail;
float q;
float md;
double  u1;
#ifdef _CALL_MATHERR
struct exception  exstruct;
#endif

  FLT2INT(x, ix);   /* copy arg to an integer */
  m = (ix >> MANTWIDTH);  /* shift off mantissa */

  if ( (0 < m) && (m < 0xff) )
  {
    /* x is positive and finite */

    if ( (ix >= lim2) || (ix <= lim1) )
    {
  
      m -= EXPBIAS;
L:
      ix &= EXPMASK;
      ix |= 0x43000000;
      INT2FLT(ix, x);

      j = ROUNDF(x);

      F = j;
      j -= 128;
    
      f = x - F;

      md = m;

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

      l_lead = md*log2_lead.f;
      l_trail = md*log2_trail.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 ( ix == one )
      return ( 0.0f );

    x = x - f_one.f;

    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 );
  }

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

#ifdef _CALL_MATHERR

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

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

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

  if ( x == Inf.f )
  {
    SETERRNO(EDOM);

    return ( Inf.f );
  }

  if ( x == 0.0f )
  {
zeroarg:

#ifdef _CALL_MATHERR

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

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

                return ( exstruct.retval );
#else
    SETERRNO(ERANGE);
    
    return ( Neginf.f );
#endif
  }

  if ( x < 0.0f )
  {
#ifdef _CALL_MATHERR

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

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

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

    return ( Qnan.f );
#endif
  }

  /* take care of denormals by scaling them up and adjusting the unbiased
     exponent of x
  */

  x *= Scaleup.f; /* multiply x by 2^23 */

  if ( x == 0.0f )
    goto zeroarg;

  FLT2INT(x, ix);   /* copy x to an integer */
  m = (ix >> MANTWIDTH);  /* shift off mantissa   */
  m -= EXPBIAS;
  m -= 23;
  goto L;
}

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