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+.\" Copyright (c) 1985, 1991 Regents of the University of California.
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     from: @(#)exp.3	6.12 (Berkeley) 7/31/91
+.\"	$Id: exp.3,v 1.7 1994/02/11 18:34:05 jtc Exp $
+.\"
+.Dd July 31, 1991
+.Dt EXP 3
+.Os BSD 4
+.Sh NAME
+.Nm exp ,
+.Nm exp2 ,
+.Nm exp10 ,
+.Nm expm1 ,
+.Nm log ,
+.Nm log2 ,
+.Nm log10 ,
+.Nm log1p ,
+.Nm pow
+.Nd exponential, logarithm, power functions
+.Sh SYNOPSIS
+.Fd #include <math.h>
+.Ft double
+.Fn exp "double x"
+.Ft double
+.Fn expm1 "double x"
+.Ft double
+.Fn log "double x"
+.Ft double
+.Fn log10 "double x"
+.Ft double
+.Fn log1p "double x"
+.Ft double
+.Fn pow "double x" "double y"
+.Sh DESCRIPTION
+The
+.Fn exp
+function computes the exponential value of the given argument
+.Fa x .
+.Pp
+The
+.Fn expm1
+function computes the value exp(x)\-1 accurately even for tiny argument
+.Fa x .
+.Pp
+The
+.Fn log
+function computes the value of the natural logarithm of argument 
+.Fa x.
+.Pp
+The
+.Fn log10
+function computes the value of the logarithm of argument
+.Fa x
+to base 10.
+.Pp
+The
+.Fn log1p
+function computes
+the value of log(1+x) accurately even for tiny argument
+.Fa x .
+.Pp
+The
+.Fn pow
+computes the value
+of
+.Ar x
+to the exponent
+.Ar y .
+.Sh ERROR (due to Roundoff etc.)
+exp(x), log(x), expm1(x) and log1p(x) are accurate to within 
+an
+.Em ulp ,
+and log10(x) to within about 2
+.Em ulps ;
+an
+.Em ulp
+is one
+.Em Unit
+in the
+.Em Last
+.Em Place .
+The error in
+.Fn pow x y
+is below about 2
+.Em ulps
+when its
+magnitude is moderate, but increases as
+.Fn pow x y
+approaches
+the over/underflow thresholds until almost as many bits could be
+lost as are occupied by the floating\-point format's exponent
+field; that is 8 bits for
+.Tn "VAX D"
+and 11 bits for IEEE 754 Double.
+No such drastic loss has been exposed by testing; the worst
+errors observed have been below 20
+.Em ulps
+for
+.Tn "VAX D" ,
+300
+.Em ulps
+for
+.Tn IEEE
+754 Double.
+Moderate values of
+.Fn pow
+are accurate enough that
+.Fn pow integer integer
+is exact until it is bigger than 2**56 on a
+.Tn VAX ,
+2**53 for
+.Tn IEEE
+754.
+.Sh RETURN VALUES
+These functions will return the appropriate computation unless an error
+occurs or an argument is out of range.
+The functions
+.Fn exp ,
+.Fn expm1
+and
+.Fn pow
+detect if the computed value will overflow,
+set the global variable
+.Va errno to
+.Er ERANGE
+and cause a reserved operand fault on a
+.Tn VAX
+or
+.Tn Tahoe .
+The function
+.Fn pow x y
+checks to see if
+.Fa x
+< 0 and
+.Fa y
+is not an integer, in the event this is true,
+the global variable
+.Va errno
+is set to
+.Er EDOM
+and on the
+.Tn VAX
+and
+.Tn Tahoe
+generate a reserved operand fault.
+On a
+.Tn VAX
+and
+.Tn Tahoe ,
+.Va errno
+is set to
+.Er EDOM
+and the reserved operand is returned
+by log unless
+.Fa x
+> 0, by
+.Fn log1p
+unless
+.Fa x
+> \-1.
+.Sh NOTES
+The functions exp(x)\-1 and log(1+x) are called
+expm1 and logp1 in
+.Tn BASIC
+on the Hewlett\-Packard
+.Tn HP Ns \-71B
+and
+.Tn APPLE
+Macintosh,
+.Tn EXP1
+and
+.Tn LN1
+in Pascal, exp1 and log1 in C
+on
+.Tn APPLE
+Macintoshes, where they have been provided to make
+sure financial calculations of ((1+x)**n\-1)/x, namely
+expm1(n\(**log1p(x))/x, will be accurate when x is tiny.
+They also provide accurate inverse hyperbolic functions.
+.Pp
+The function
+.Fn pow x 0
+returns x**0 = 1 for all x including x = 0,
+.if n \
+Infinity
+.if t \
+\(if
+(not found on a
+.Tn VAX ) ,
+and
+.Em NaN
+(the reserved
+operand on a
+.Tn VAX ) .  Previous implementations of pow may
+have defined x**0 to be undefined in some or all of these
+cases.  Here are reasons for returning x**0 = 1 always:
+.Bl -enum -width indent
+.It
+Any program that already tests whether x is zero (or
+infinite or \*(Na) before computing x**0 cannot care
+whether 0**0 = 1 or not. Any program that depends
+upon 0**0 to be invalid is dubious anyway since that
+expression's meaning and, if invalid, its consequences 
+vary from one computer system to another.
+.It
+Some Algebra texts (e.g. Sigler's) define x**0 = 1 for 
+all x, including x = 0.
+This is compatible with the convention that accepts a[0]
+as the value of polynomial
+.Bd -literal -offset indent
+p(x) = a[0]\(**x**0 + a[1]\(**x**1 + a[2]\(**x**2 +...+ a[n]\(**x**n
+.Ed
+.Pp
+at x = 0 rather than reject a[0]\(**0**0 as invalid.
+.It
+Analysts will accept 0**0 = 1 despite that x**y can
+approach anything or nothing as x and y approach 0
+independently.
+The reason for setting 0**0 = 1 anyway is this:
+.Bd -filled -offset indent
+If x(z) and y(z) are
+.Em any
+functions analytic (expandable
+in power series) in z around z = 0, and if there 
+x(0) = y(0) = 0, then x(z)**y(z) \(-> 1 as z \(-> 0.
+.Ed
+.It
+If 0**0 = 1, then
+.if n \
+infinity**0 = 1/0**0 = 1 too; and
+.if t \
+\(if**0 = 1/0**0 = 1 too; and
+then \*(Na**0 = 1 too because x**0 = 1 for all finite
+and infinite x, i.e., independently of x.
+.El
+.Sh SEE ALSO
+.Xr math 3 ,
+.Xr infnan 3
+.Sh HISTORY
+A
+.Fn exp ,
+.Fn log
+and
+.Fn pow
+functions
+appeared in
+.At v6 .
+A
+.Fn log10
+function
+appeared in
+.At v7 .
+The
+.Fn log1p
+and
+.Fn expm1
+functions appeared in
+.Bx 4.3 .