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Portions of this text are reprinted and reproduced in electronic form in the Sun OS Reference Manual, from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between these versions and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html. 8 .\" This notice shall appear on any product containing this material. 9 .\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License"). You may not use this file except in compliance with the License. 10 .\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing. See the License for the specific language governing permissions and limitations under the License. 11 .\" When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner] 12 .TH log 3M "12 Jul 2006" "SunOS 5.11" "Mathematical Library Functions" 13 .SH NAME 14 log, logf, logl \- natural logarithm function 15 .SH SYNOPSIS 16 .LP 17 .nf 18 c99 [ \fIflag\fR... ] \fIfile\fR... \fB-lm\fR [ \fIlibrary\fR... ] 19 #include <math.h> 20 21 \fBdouble\fR \fBlog\fR(\fBdouble\fR \fIx\fR); 22 .fi 23 24 .LP 25 .nf 26 \fBfloat\fR \fBlogf\fR(\fBfloat\fR \fIx\fR); 27 .fi 28 29 .LP 30 .nf 31 \fBlong double\fR \fBlogl\fR(\fBlong double\fR \fIx\fR); 32 .fi 33 34 .SH DESCRIPTION 35 .sp 36 .LP 37 These functions compute the natural logarithm of their argument \fIx\fR, 38 log(\fIe\fR)(\fIx\fR). 39 .SH RETURN VALUES 40 .sp 41 .LP 42 Upon successful completion, \fBlog()\fR returns the natural logarithm of 43 \fIx\fR. 44 .sp 45 .LP 46 If \fIx\fR is \(+-0, a pole error occurs and \fBlog()\fR, \fBlogf()\fR, and 47 \fBlogl()\fR return \(mi\fBHUGE_VAL\fR, \(mi\fBHUGE_VALF\fR, and 48 \(mi\fBHUGE_VALL\fR, respectively. 49 .sp 50 .LP 51 For finite values of \fIx\fR that are less than 0, or if \fIx\fR is \(miInf, a 52 domain error occurs and a NaN is returned. 53 .sp 54 .LP 55 If \fIx\fR is NaN, a NaN is returned. 56 .sp 57 .LP 58 If \fIx\fR is 1, +0 is returned. 59 .sp 60 .LP 61 If \fIx\fR is +Inf, \fIx\fR is returned. 62 .sp 63 .LP 64 For exceptional cases, \fBmatherr\fR(3M) tabulates the values to be returned by 65 \fBlog()\fR as specified by SVID3 and XPG3. 66 .SH ERRORS 67 .sp 68 .LP 69 These functions will fail if: 70 .sp 71 .ne 2 72 .mk 73 .na 74 \fBDomain Error\fR 75 .ad 76 .RS 16n 77 .rt 78 The finite value of \fIx\fR is negative, or \fIx\fR is -Inf. 79 .sp 80 If the integer expression (\fBmath_errhandling\fR & \fBMATH_ERREXCEPT\fR) is 81 non-zero, the invalid floating-point exception is raised. 82 .sp 83 The \fBlog()\fR function sets \fBerrno\fR to \fBEDOM\fR if the value of \fIx\fR 84 is negative. 85 .RE 86 87 .sp 88 .ne 2 89 .mk 90 .na 91 \fBPole Error\fR 92 .ad 93 .RS 16n 94 .rt 95 The value of \fIx\fR is 0. 96 .sp 97 If the integer expression (\fBmath_errhandling\fR & \fBMATH_ERREXCEPT\fR) is 98 non-zero, the divide-by-zero floating-point exception is raised. 99 .RE 100 101 .SH USAGE 102 .sp 103 .LP 104 An application wanting to check for exceptions should call 105 \fBfeclearexcept\fR(\fBFE_ALL_EXCEPT\fR) before calling these functions. On 106 return, if \fBfetestexcept\fR(\fBFE_INVALID\fR | \fBFE_DIVBYZERO\fR | 107 \fBFE_OVERFLOW\fR | \fBFE_UNDERFLOW\fR) is non-zero, an exception has been 108 raised. An application should either examine the return value or check the 109 floating point exception flags to detect exceptions. 110 .sp 111 .LP 112 An application can also set \fBerrno\fR to 0 before calling \fBlog()\fR. On 113 return, if \fBerrno\fR is non-zero, an error has occurred. The \fBlogf()\fR and 114 \fBlogl()\fR functions do not set \fBerrno\fR. 115 .SH ATTRIBUTES 116 .sp 117 .LP 118 See \fBattributes\fR(5) for descriptions of the following attributes: 119 .sp 120 121 .sp 122 .TS 123 tab() box; 124 cw(2.75i) |cw(2.75i) 125 lw(2.75i) |lw(2.75i) 126 . 127 ATTRIBUTE TYPEATTRIBUTE VALUE 128 _ 129 Interface StabilityStandard 130 _ 131 MT-LevelMT-Safe 132 .TE 133 134 .SH SEE ALSO 135 .sp 136 .LP 137 \fBexp\fR(3M), \fBfeclearexcept\fR(3M), \fBfetestexcept\fR(3M), 138 \fBisnan\fR(3M), \fBlog10\fR(3M), \fBlog1p\fR(3M), \fBmath.h\fR(3HEAD), 139 \fBmatherr\fR(3M), \fBattributes\fR(5), \fBstandards\fR(5)