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32 .\" from: @(#)exp.3 6.12 (Berkeley) 7/31/91
33 .\" $FreeBSD: src/lib/msun/man/exp.3,v 1.9.2.4 2001/12/17 10:08:36 ru Exp $
34 .\" $DragonFly: src/lib/msun/man/Attic/exp.3,v 1.2 2003/06/17 04:26:52 dillon Exp $
54 .Nd exponential, logarithm, power functions
80 .Fn pow "double x" "double y"
82 .Fn powf "float x" "float y"
88 functions compute the exponential value of the given argument
95 functions compute the value exp(x)\-1 accurately even for tiny argument
102 functions compute the value of the natural logarithm of argument
109 functions compute the value of the logarithm of argument
118 the value of log(1+x) accurately even for tiny argument
125 functions compute the value
130 .Sh ERROR (due to Roundoff etc.)
136 are accurate to within
155 magnitude is moderate, but increases as
158 the over/underflow thresholds until almost as many bits could be
159 lost as are occupied by the floating\-point format's exponent
160 field; that is 8 bits for
162 and 11 bits for IEEE 754 Double.
163 No such drastic loss has been exposed by testing; the worst
164 errors observed have been below 20
175 are accurate enough that
176 .Fn pow integer integer
177 is exact until it is bigger than 2**56 on a
183 These functions will return the appropriate computation unless an error
184 occurs or an argument is out of range.
189 detect if the computed value will overflow,
190 set the global variable
194 and cause a reserved operand fault on a
204 is not an integer, in the event this is true,
213 generate a reserved operand fault.
221 and the reserved operand is returned
230 The functions exp(x)\-1 and log(1+x) are called
233 on the Hewlett\-Packard
241 in Pascal, exp1 and log1 in C
244 Macintoshes, where they have been provided to make
245 sure financial calculations of ((1+x)**n\-1)/x, namely
246 expm1(n\(**log1p(x))/x, will be accurate when x is tiny.
247 They also provide accurate inverse hyperbolic functions.
251 returns x**0 = 1 for all x including x = 0,
263 Previous implementations of pow may
264 have defined x**0 to be undefined in some or all of these
265 cases. Here are reasons for returning x**0 = 1 always:
266 .Bl -enum -width indent
268 Any program that already tests whether x is zero (or
269 infinite or \*(Na) before computing x**0 cannot care
270 whether 0**0 = 1 or not.
271 Any program that depends
272 upon 0**0 to be invalid is dubious anyway since that
273 expression's meaning and, if invalid, its consequences
274 vary from one computer system to another.
276 Some Algebra texts (e.g. Sigler's) define x**0 = 1 for
277 all x, including x = 0.
278 This is compatible with the convention that accepts a[0]
279 as the value of polynomial
280 .Bd -literal -offset indent
281 p(x) = a[0]\(**x**0 + a[1]\(**x**1 + a[2]\(**x**2 +...+ a[n]\(**x**n
284 at x = 0 rather than reject a[0]\(**0**0 as invalid.
286 Analysts will accept 0**0 = 1 despite that x**y can
287 approach anything or nothing as x and y approach 0
289 The reason for setting 0**0 = 1 anyway is this:
290 .Bd -ragged -offset indent
293 functions analytic (expandable
294 in power series) in z around z = 0, and if there
295 x(0) = y(0) = 0, then x(z)**y(z) \(-> 1 as z \(-> 0.
300 infinity**0 = 1/0**0 = 1 too; and
302 \(if**0 = 1/0**0 = 1 too; and
303 then \*(Na**0 = 1 too because x**0 = 1 for all finite
304 and infinite x, i.e., independently of x.
326 functions appeared in