1 
2 /* @(#)w_log.c 5.1 93/09/24 */
3 /*
4  * ====================================================
5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6  *
7  * Developed at SunPro, a Sun Microsystems, Inc. business.
8  * Permission to use, copy, modify, and distribute this
9  * software is freely granted, provided that this notice
10  * is preserved.
11  * ====================================================
12  */
13 
14 /*
15 FUNCTION
16        <<log>>, <<logf>>---natural logarithms
17 
18 INDEX
19     log
20 INDEX
21     logf
22 
23 ANSI_SYNOPSIS
24        #include <math.h>
25        double log(double <[x]>);
26        float logf(float <[x]>);
27 
28 TRAD_SYNOPSIS
29        #include <math.h>
30        double log(<[x]>);
31        double <[x]>;
32 
33        float logf(<[x]>);
34        float <[x]>;
35 
36 DESCRIPTION
37 Return the natural logarithm of <[x]>, that is, its logarithm base e
38 (where e is the base of the natural system of logarithms, 2.71828@dots{}).
39 <<log>> and <<logf>> are identical save for the return and argument types.
40 
41 You can use the (non-ANSI) function <<matherr>> to specify error
42 handling for these functions.
43 
44 RETURNS
45 Normally, returns the calculated value.  When <[x]> is zero, the
46 returned value is <<-HUGE_VAL>> and <<errno>> is set to <<ERANGE>>.
47 When <[x]> is negative, the returned value is <<-HUGE_VAL>> and
48 <<errno>> is set to <<EDOM>>.  You can control the error behavior via
49 <<matherr>>.
50 
51 PORTABILITY
52 <<log>> is ANSI, <<logf>> is an extension.
53 */
54 
55 /*
56  * wrapper log(x)
57  */
58 
59 #include "fdlibm.h"
60 #include <errno.h>
61 
62 #ifndef _DOUBLE_IS_32BITS
63 
64 #ifdef __STDC__
log(double x)65 	double log(double x)		/* wrapper log */
66 #else
67 	double log(x)			/* wrapper log */
68 	double x;
69 #endif
70 {
71 #ifdef _IEEE_LIBM
72 	return __ieee754_log(x);
73 #else
74 	double z;
75 	struct exception exc;
76 	z = __ieee754_log(x);
77 	if(_LIB_VERSION == _IEEE_ || isnan(x) || x > 0.0) return z;
78 #ifndef HUGE_VAL
79 #define HUGE_VAL inf
80 	double inf = 0.0;
81 
82 	SET_HIGH_WORD(inf,0x7ff00000);	/* set inf to infinite */
83 #endif
84 	exc.name = "log";
85 	exc.err = 0;
86 	exc.arg1 = x;
87 	exc.arg2 = x;
88 	if (_LIB_VERSION == _SVID_)
89            exc.retval = -HUGE;
90 	else
91 	   exc.retval = -HUGE_VAL;
92 	if(x==0.0) {
93 	    /* log(0) */
94 	    exc.type = SING;
95 	    if (_LIB_VERSION == _POSIX_)
96 	       errno = ERANGE;
97 	    else if (!matherr(&exc)) {
98 	       errno = EDOM;
99 	    }
100 	} else {
101 	    /* log(x<0) */
102 	    exc.type = DOMAIN;
103 	    if (_LIB_VERSION == _POSIX_)
104 	       errno = EDOM;
105 	    else if (!matherr(&exc)) {
106 	       errno = EDOM;
107 	    }
108         }
109 	if (exc.err != 0)
110            errno = exc.err;
111         return exc.retval;
112 #endif
113 }
114 
115 #endif /* defined(_DOUBLE_IS_32BITS) */
116