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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. 7 .\" This notice shall appear on any product containing this material. 8 .\" 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. 9 .\" 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. 10 .\" 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] 11 .TH log2 3M "12 Jul 2006" "SunOS 5.11" "Mathematical Library Functions" 12 .SH NAME 13 log2, log2f, log2l \- compute base 2 logarithm functions 14 .SH SYNOPSIS 15 .LP 16 .nf 17 c99 [ \fIflag\fR... ] \fIfile\fR... \fB-lm\fR [ \fIlibrary\fR... ] 18 #include <math.h> 19 20 \fBdouble\fR \fBlog2\fR(\fBdouble\fR \fIx\fR); 21 .fi 22 23 .LP 24 .nf 25 \fBfloat\fR \fBlog2f\fR(\fBfloat\fR \fIx\fR); 26 .fi 27 28 .LP 29 .nf 30 \fBlong double\fR \fBlog2l\fR(\fBlong double\fR \fIx\fR); 31 .fi 32 33 .SH DESCRIPTION 34 .sp 35 .LP 36 These functions compute the base 2 logarithm of their argument \fIx\fR, 37 \fBlog2\fR(\fIx\fR). 38 .SH RETURN VALUES 39 .sp 40 .LP 41 Upon successful completion, these functions return the base 2 logarithm of 42 \fIx\fR. 43 .sp 44 .LP 45 If \fIx\fR is \(+-0, a pole error occurs and \fBlog2()\fR, \fBlog2f()\fR, and 46 \fBlog2l()\fR return \(mi\fBHUGE_VAL\fR, \(mi\fBHUGE_VALF\fR, and 47 \(mi\fBHUGE_VALL\fR, respectively. 48 .sp 49 .LP 50 For finite values of \fIx\fR that are less than 0, or if \fIx\fR is \(miInf a 51 domain error occurs and a NaN is returned. 52 .sp 53 .LP 54 If \fIx\fR is NaN, a NaN is returned. 55 .sp 56 .LP 57 If \fIx\fR is 1, +0 is returned. 58 .sp 59 .LP 60 If \fIx\fR is +Inf, \fIx\fR is returned. 61 .SH ERRORS 62 .sp 63 .LP 64 These functions will fail if: 65 .sp 66 .ne 2 67 .mk 68 .na 69 \fBDomain Error\fR 70 .ad 71 .RS 16n 72 .rt 73 The finite value of \fIx\fR is less than 0, or \fIx\fR is \(miInf. 74 .sp 75 If the integer expression (\fBmath_errhandling\fR & \fBMATH_ERREXCEPT\fR) is 76 non-zero, then the invalid floating-point exception is raised. 77 .RE 78 79 .sp 80 .ne 2 81 .mk 82 .na 83 \fBPole Error\fR 84 .ad 85 .RS 16n 86 .rt 87 The value of \fIx\fR is 0. 88 .sp 89 If the integer expression (\fBmath_errhandling\fR & \fBMATH_ERREXCEPT\fR) is 90 non-zero, then the divide-by-zero floating-point exception is raised. 91 .RE 92 93 .SH USAGE 94 .sp 95 .LP 96 An application wanting to check for exceptions should call 97 \fBfeclearexcept\fR(\fBFE_ALL_EXCEPT\fR) before calling these functions. On 98 return, if \fBfetestexcept\fR(\fBFE_INVALID\fR | \fBFE_DIVBYZERO\fR | 99 \fBFE_OVERFLOW\fR | \fBFE_UNDERFLOW\fR) is non-zero, an exception has been 100 raised. An application should either examine the return value or check the 101 floating point exception flags to detect exceptions. 102 .SH ATTRIBUTES 103 .sp 104 .LP 105 See \fBattributes\fR(5) for descriptions of the following attributes: 106 .sp 107 108 .sp 109 .TS 110 tab() box; 111 cw(2.75i) |cw(2.75i) 112 lw(2.75i) |lw(2.75i) 113 . 114 ATTRIBUTE TYPEATTRIBUTE VALUE 115 _ 116 Interface StabilityStandard 117 _ 118 MT-LevelMT-Safe 119 .TE 120 121 .SH SEE ALSO 122 .sp 123 .LP 124 \fBfeclearexcept\fR(3M), \fBfetestexcept\fR(3M), \fBlog\fR(3M), 125 \fBmath.h\fR(3HEAD), \fBattributes\fR(5), \fBstandards\fR(5)