w_log.c

gcc的组建

/* @(#)w_log.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

/*
FUNCTION
       <<log>>, <<logf>>---natural logarithms

INDEX
    log
INDEX
    logf

ANSI_SYNOPSIS
       #include <math.h>
       double log(double <[x]>);
       float logf(float <[x]>);

TRAD_SYNOPSIS
       #include <math.h>
       double log(<[x]>);
       double <[x]>;

       float logf(<[x]>);
       float <[x]>;

DESCRIPTION
Return the natural logarithm of <[x]>, that is, its logarithm base e
(where e is the base of the natural system of logarithms, 2.71828@dots{}).
<<log>> and <<logf>> are identical save for the return and argument types.

You can use the (non-ANSI) function <<matherr>> to specify error
handling for these functions. 

RETURNS
Normally, returns the calculated value.  When <[x]> is zero, the
returned value is <<-HUGE_VAL>> and <<errno>> is set to <<ERANGE>>.
When <[x]> is negative, the returned value is <<-HUGE_VAL>> and
<<errno>> is set to <<EDOM>>.  You can control the error behavior via
<<matherr>>.

PORTABILITY
<<log>> is ANSI, <<logf>> is an extension.
*/

/*
 * wrapper log(x)
 */

#include "fdlibm.h"
#include <errno.h>

#ifndef _DOUBLE_IS_32BITS

#ifdef __STDC__
	double log(double x)		/* wrapper log */
#else
	double log(x)			/* wrapper log */
	double x;
#endif
{
#ifdef _IEEE_LIBM
	return __ieee754_log(x);
#else
	double z;
	struct exception exc;
	z = __ieee754_log(x);
	if(_LIB_VERSION == _IEEE_ || isnan(x) || x > 0.0) return z;
#ifndef HUGE_VAL 
#define HUGE_VAL inf
	double inf = 0.0;

	SET_HIGH_WORD(inf,0x7ff00000);	/* set inf to infinite */
#endif
	exc.name = "log";
	exc.err = 0;
	exc.arg1 = x;
	exc.arg2 = x;
	if (_LIB_VERSION == _SVID_)
           exc.retval = -HUGE;
	else
	   exc.retval = -HUGE_VAL;
	if(x==0.0) {
	    /* log(0) */
	    exc.type = SING;
	    if (_LIB_VERSION == _POSIX_)
	       errno = ERANGE;
	    else if (!matherr(&exc)) {
	       errno = EDOM;
	    }
	} else { 
	    /* log(x<0) */
	    exc.type = DOMAIN;
	    if (_LIB_VERSION == _POSIX_)
	       errno = EDOM;
	    else if (!matherr(&exc)) {
	       errno = EDOM;
	    }
        }
	if (exc.err != 0)
           errno = exc.err;
        return exc.retval; 
#endif
}

#endif /* defined(_DOUBLE_IS_32BITS) */