1.\" Copyright (c) 1985, 1991 Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" from: @(#)ieee.3 6.4 (Berkeley) 5/6/91 29.\" 30.Dd December 16, 2007 31.Dt ILOGB 3 32.Os 33.Sh NAME 34.Nm ilogb , 35.Nm ilogbf , 36.Nm ilogbl , 37.Nm logb , 38.Nm logbf , 39.Nm logbl 40.Nd extract exponent 41.Sh LIBRARY 42.Lb libm 43.Sh SYNOPSIS 44.In math.h 45.Ft int 46.Fn ilogb "double x" 47.Ft int 48.Fn ilogbf "float x" 49.Ft int 50.Fn ilogbl "long double x" 51.Ft double 52.Fn logb "double x" 53.Ft float 54.Fn logbf "float x" 55.Ft long double 56.Fn logbl "long double x" 57.Sh DESCRIPTION 58.Fn ilogb , 59.Fn ilogbf 60and 61.Fn ilogbl 62return 63.Fa x Ns 's exponent 64in integer format. 65.Fn ilogb \*(Pm\*(If 66returns 67.Dv INT_MAX , 68.Fn ilogb \*(Pm\*(Na 69returns 70.Dv FP_ILOGBNAN , 71and 72.Fn ilogb 0 73returns 74.Dv FP_ILOGB0 . 75.Pp 76.Fn logb x , 77.Fn logbf x , 78and 79.Fn logbl x 80return 81.Fa x Ns 's exponent 82in floating\-point format with the same precision as 83.Fa x . 84.Fn logb \*(Pm\*(If 85returns +\*(If, and 86.Fn logb 0 87returns -\*(If with a division by zero exception. 88.Sh SEE ALSO 89.Xr frexp 3 , 90.Xr ieee 3 , 91.Xr math 3 , 92.Xr scalbn 3 93.Sh STANDARDS 94The 95.Fn ilogb , 96.Fn ilogbf , 97.Fn ilogbl , 98.Fn logb , 99.Fn logbf , 100and 101.Fn logbl 102routines conform to 103.St -isoC-99 . 104The latter three 105implement the logb function recommended by 106.St -ieee754 . 107.Sh HISTORY 108.Bl -tag -width "Function " -compact 109.It Em Function 110.Em "First Appeared In" 111.It Fn logb 112.Bx 4.3 113.It Fn ilogb 114.Fx 1.1.5 115.It Fn ilogbf 116.Fx 2.0 117.It Fn logbf 118.Fx 2.0 119.It Fn ilogbl 120.Fx 5.4 121.It Fn logbl 122.Fx 8.0 123.El 124