log1p, log1pf, log1pl

Computes the natural logarithm of 1 plus the specified value.

Syntax

double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);

#define log1p(X) // Requires C11 or later

float log1p(float x); //C++ only
long double log1p(long double x); //C++ only

Parameters

x
The floating-point argument.

Return value

If successful, returns the natural (base-e) log of (x + 1).

Otherwise, may return one of the following values:

The errno value is set to ERANGE if x = -1. The errno value is set to EDOM if x < -1.

Remarks

The log1p functions may be more accurate than using log(x + 1) when x is near 0.

Because C++ allows overloading, you can call overloads of log1p that take and return float and long double types. In a C program, unless you're using the <tgmath.h> macro to call this function, log1p always takes and returns a double.

If you use the <tgmath.h> log1p() macro, the type of the argument determines which version of the function is selected. See Type-generic math for details.

Where x is a natural number, this function returns the base e logarithm of x + 1.

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.

Requirements

For more compatibility information, see Compatibility.

See also

Alphabetical function reference
log2, log2f, log2l
log, logf, log10, log10f