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.\" $FreeBSD$ 30.\" 31.Dd December 16, 2007 32.Dt ILOGB 3 33.Os 34.Sh NAME 35.Nm ilogb , 36.Nm ilogbf , 37.Nm ilogbl , 38.Nm logb , 39.Nm logbf , 40.Nm logbl 41.Nd extract exponent 42.Sh LIBRARY 43.Lb libm 44.Sh SYNOPSIS 45.In math.h 46.Ft int 47.Fn ilogb "double x" 48.Ft int 49.Fn ilogbf "float x" 50.Ft int 51.Fn ilogbl "long double x" 52.Ft double 53.Fn logb "double x" 54.Ft float 55.Fn logbf "float x" 56.Ft long double 57.Fn logbl "long double x" 58.Sh DESCRIPTION 59.Fn ilogb , 60.Fn ilogbf 61and 62.Fn ilogbl 63return 64.Fa x Ns 's exponent 65in integer format. 66.Fn ilogb \*(Pm\*(If 67returns 68.Dv INT_MAX , 69.Fn ilogb \*(Pm\*(Na 70returns 71.Dv FP_ILOGBNAN , 72and 73.Fn ilogb 0 74returns 75.Dv FP_ILOGB0 . 76.Pp 77.Fn logb x , 78.Fn logbf x , 79and 80.Fn logbl x 81return 82.Fa x Ns 's exponent 83in floating\-point format with the same precision as 84.Fa x . 85.Fn logb \*(Pm\*(If 86returns +\*(If, and 87.Fn logb 0 88returns -\*(If with a division by zero exception. 89.Sh SEE ALSO 90.Xr frexp 3 , 91.Xr ieee 3 , 92.Xr math 3 , 93.Xr scalbn 3 94.Sh STANDARDS 95The 96.Fn ilogb , 97.Fn ilogbf , 98.Fn ilogbl , 99.Fn logb , 100.Fn logbf , 101and 102.Fn logbl 103routines conform to 104.St -isoC-99 . 105The latter three 106implement the logb function recommended by 107.St -ieee754 . 108.Sh HISTORY 109.Bl -tag -width "Function " -compact 110.It Em Function 111.Em "First Appeared In" 112.It Fn logb 113.Bx 4.3 114.It Fn ilogb 115.Fx 1.1.5 116.It Fn ilogbf 117.Fx 2.0 118.It Fn logbf 119.Fx 2.0 120.It Fn ilogbl 121.Fx 5.4 122.It Fn logbl 123.Fx 8.0 124.El 125