w_log10.c

来自「Newlib 嵌入式 C库 标准实现代码」· C语言 代码 · 共 117 行

/* @(#)w_log10.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
	<<log10>>, <<log10f>>---base 10 logarithms

INDEX
log10
INDEX
log10f

ANSI_SYNOPSIS
	#include <math.h>
	double log10(double <[x]>);
	float log10f(float <[x]>);

TRAD_SYNOPSIS
	#include <math.h>
	double log10(<[x]>)
	double <[x]>;

	float log10f(<[x]>)
	float <[x]>;

DESCRIPTION
<<log10>> returns the base 10 logarithm of <[x]>.
It is implemented as <<log(<[x]>) / log(10)>>.

<<log10f>> is identical, save that it takes and returns <<float>> values.

RETURNS
<<log10>> and <<log10f>> return the calculated value. 

See the description of <<log>> for information on errors.

PORTABILITY
<<log10>> is ANSI C.  <<log10f>> is an extension.

 */

/* 
 * wrapper log10(X)
 */

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

#ifndef _DOUBLE_IS_32BITS

#ifdef __STDC__
	double log10(double x)		/* wrapper log10 */
#else
	double log10(x)			/* wrapper log10 */
	double x;
#endif
{
#ifdef _IEEE_LIBM
	return __ieee754_log10(x);
#else
	double z;
	struct exception exc;
	z = __ieee754_log10(x);
	if(_LIB_VERSION == _IEEE_ || isnan(x)) return z;
	if(x<=0.0) {
#ifndef HUGE_VAL 
#define HUGE_VAL inf
	    double inf = 0.0;

	    SET_HIGH_WORD(inf,0x7ff00000);	/* set inf to infinite */
#endif
	    exc.name = "log10";
	    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) {
	        /* log10(0) */
	        exc.type = SING;
	        if (_LIB_VERSION == _POSIX_)
	           errno = ERANGE;
	        else if (!matherr(&exc)) {
	           errno = ERANGE;
	        }
	    } else { 
	        /* log10(x<0) */
	        exc.type = DOMAIN;
	        if (_LIB_VERSION == _POSIX_)
	           errno = EDOM;
	        else if (!matherr(&exc)) {
	           errno = EDOM;
	        }
                exc.retval = nan("");
            }
	    if (exc.err != 0)
               errno = exc.err;
            return exc.retval; 
	} else
	    return z;
#endif
}

#endif /* defined(_DOUBLE_IS_32BITS) */