std::log1p,std::log1pf,std::log1pl (3) - Linux Manuals
Defined in header <cmath>
float log1p ( float arg ); (1) (since C++11)
float log1pf( float arg );
double log1p ( double arg ); (2) (since C++11)
long double log1p ( long double arg ); (3) (since C++11)
long double log1pl( long double arg );
double log1p ( IntegralType arg ); (4) (since C++11)
1-3) Computes the natural (base e) logarithm of 1+arg. This function is more precise than the expression std::log(1+arg) if arg is close to zero.
4) A set of overloads or a function template accepting an argument of any integral_type. Equivalent to 2) (the argument is cast to double).
arg - value of floating-point or Integral_type
If no errors occur ln(1+arg) is returned.
If a domain error occurs, an implementation-defined value is returned (NaN where supported)
If a pole error occurs, -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL is returned.
If a range error occurs due to underflow, the correct result (after rounding) is returned.
Errors are reported as specified in math_errhandling.
Domain error occurs if arg is less than -1.
Pole error may occur if arg is -1.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
* If the argument is ±0, it is returned unmodified
* If the argument is -1, -∞ is returned and FE_DIVBYZERO is raised.
* If the argument is less than -1, NaN is returned and FE_INVALID is raised.
* If the argument is +∞, +∞ is returned
* If the argument is NaN, NaN is returned
The functions std::expm1 and std::log1p are useful for financial calculations, for example, when calculating small daily interest rates: (1+x)n
-1 can be expressed as std::expm1(n * std::log1p(x)). These functions also simplify writing accurate inverse hyperbolic functions.
// Run this code
logl computes natural (base e) logarithm (ln(x))
log10l computes common (base 10) logarithm (log10(x))
log2l base 2 logarithm of the given number (log2(x))
expm1l returns e raised to the given power, minus one (ex-1)