exp(3) — Subroutines

NAME

exp, expm1, log, log2, log10, log1p, pow − Exponential, logarithm, and power functions

LIBRARY

Math Library (libm.a)

SYNOPSIS

#include <math.h>

double exp    (double x);
float expf   (float x);
long double expl    (long double x);
double expm1 (double x);
float expm1f (float x);
long double expm1l (long double x);
double log    (double x);
float logf   (float x);
long double logl    (long double x);
double log2   (double x);
float log2f (float x);
long double log2l   (long double x);
double log10 (double x);
float log10f (float x);
long double log10l (long double x);
double log1p (double y);
float log1pf (float y);
long double log1pl (long double y);
double pow    (double x, double y);
float powf   (float x, float y);
long double powl    (long double x, long double y);

STANDARDS

Interfaces documented on this reference page conform to industry standards as follows:

exp(): XPG4

expm1(): XPG4−UNIX

log(): XPG4

log10(): XPG4

log1p(): XPG4−UNIX

pow(): XPG4

Refer to the standards(5) reference page for more information about industry standards and associated tags.

DESCRIPTION

The exp(), expf(), and expl() functions compute the value of the exponential function, defined as e∗∗x, where e is the constant used as a base for natural logarithms.

The expm1(), expm1f(), and expm1l() functions compute exp(x) − 1 accurately, even for tiny x.

The log(), logf(), and logl() functions compute the natural (base e) logarithm of x.

The log2(), log2f(), and log2l() functions compute the base 2 logarithm of x.

The log10(), log10f(), and log10l() functions compute the common (base 10) logarithm of x.

The log1p(), log1pf(), and log1pl() functions compute log(1+y) accurately, even for tiny y.

The pow(), powf(), and powl() functions raise a floating-point base x to a floating-point exponent y. The value of pow(x,y) is computed as e∗∗(y ln(x)) for positive x. If x is 0 or negative, see your language reference manual.

Passing a NaN input value to pow() produces a NaN result for y not equal to 0. For pow(NaN,0), see your language reference manual.

The following table describes function behavior in response to exceptional arguments:

Function	Exceptional Argument	Routine Behavior
exp(), expf(), expl()	x > ln(max_float)	Overflow
exp(), expf(), expl()	x < ln(min_float)	Underflow
expm1(), expm1f(), expm1l()	x > ln(max_float)	Overflow
expm1(), expm1f(), expm1l()	x < ln(min_float)	Underflow
log(), logf(), logl()	x < 0	Invalid argument
log(), logf(), logl()	x = 0	Overflow
log2(), log2f(), log2l()	x < 0	Invalid argument
log2(), logf2(), log2l()	x = 0	Overflow
log10(), log10f(), log10l()	x < 0	Invalid argument
log10(), log10f(), log10l()	x = 0	Overflow
log1p(), log1pf(), log1pl()	1+y < 0	Invalid argument
log1p(), log1pf(), log1pl()	1+y = 0	Overflow
pow(), powf(), powl()	y ln(x) > ln(max_float)	Overflow
pow(), powf(), powl()	y ln(x) < ln(min_float)	Underflow

The following table lists boundary values used by these functions: