DragonFly On-Line Manual Pages
EXP(3) DragonFly Library Functions Manual EXP(3)
exp, expf, exp2, exp2f, exp2l, expm1, expm1f, pow, powf -- exponential
and power functions
Math Library (libm, -lm)
exp2l(long double x);
pow(double x, double y);
powf(float x, float y);
The exp() and the expf() functions compute the base e exponential value
of the given argument x.
The exp2(), exp2f(), and exp2l() functions compute the base 2 exponential
of the given argument x.
The expm1() and the expm1f() functions compute the value exp(x)-1 accu-
rately even for tiny argument x.
The pow() and the powf() functions compute the value of x to the exponent
ERROR (due to Roundoff etc.)
The values of exp(0), expm1(0), exp2(integer), and pow(integer, integer)
are exact provided that they are representable. Otherwise the error in
these functions is generally below one ulp.
These functions will return the appropriate computation unless an error
occurs or an argument is out of range. The functions pow(x, y) and
powf(x, y) raise an invalid exception and return an NaN if x < 0 and y is
not an integer.
The function pow(x, 0) returns x**0 = 1 for all x including x = 0, infin-
ity, and NaN . Previous implementations of pow may have defined x**0 to
be undefined in some or all of these cases. Here are reasons for return-
ing x**0 = 1 always:
1. Any program that already tests whether x is zero (or infinite or
NaN) before computing x**0 cannot care whether 0**0 = 1 or not.
Any program that depends upon 0**0 to be invalid is dubious any-
way since that expression's meaning and, if invalid, its conse-
quences vary from one computer system to another.
2. 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 as the value of polynomial
p(x) = a*x**0 + a*x**1 + a*x**2 +...+ a[n]*x**n
at x = 0 rather than reject a*0**0 as invalid.
3. Analysts will accept 0**0 = 1 despite that x**y can approach any-
thing or nothing as x and y approach 0 independently. The reason
for setting 0**0 = 1 anyway is this:
If x(z) and y(z) are 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.
4. If 0**0 = 1, then infinity**0 = 1/0**0 = 1 too; and then NaN**0 =
1 too because x**0 = 1 for all finite and infinite x, i.e., inde-
pendently of x.
fenv(3), ldexp(3), log(3), math(3)
These functions conform to ISO/IEC 9899:1999 (``ISO C99'').
DragonFly 3.5 December 21, 2011 DragonFly 3.5