[edit]Parameters

[edit]Return value

If no errors occurln(1+num) 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.

[edit]Error handling

Errors are reported as specified inmath_errhandling.

Domain error occurs ifnum is less than-1.

Pole error may occur ifnum 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 andFE_DIVBYZERO is raised.
• If the argument is less than -1, NaN is returned andFE_INVALID is raised.
• If the argument is +∞, +∞ is returned.
• If the argument is NaN, NaN is returned.

[edit]Notes

The functionsstd::expm1 andstd::log1p are useful for financial calculations, for example, when calculating small daily interest rates:(1 + x)n
- 1 can be expressed asstd::expm1(n* std::log1p(x)). These functions also simplify writing accurate inverse hyperbolic functions.

The additional overloads are not required to be provided exactly as(A). They only need to be sufficient to ensure that for their argumentnum of integer type,std::log1p(num) has the same effect asstd::log1p(static_cast<double>(num)).

[edit]Example

#include <cerrno>#include <cfenv>#include <cmath>#include <cstring>#include <iostream>// #pragma STDC FENV_ACCESS ON int main(){std::cout<<"log1p(0) = "<< log1p(0)<<'\n'<<"Interest earned in 2 days on $100, compounded daily at 1%\n"<<"    on a 30/360 calendar = "<<100* expm1(2* log1p(0.01/360))<<'\n'<<"log(1+1e-16) = "<<std::log(1+1e-16)<<", but log1p(1e-16) = "<< std::log1p(1e-16)<<'\n'; // special valuesstd::cout<<"log1p(-0) = "<< std::log1p(-0.0)<<'\n'<<"log1p(+Inf) = "<< std::log1p(INFINITY)<<'\n'; // error handlingerrno=0;std::feclearexcept(FE_ALL_EXCEPT); std::cout<<"log1p(-1) = "<< std::log1p(-1)<<'\n'; if(errno==ERANGE)std::cout<<"    errno == ERANGE: "<<std::strerror(errno)<<'\n';if(std::fetestexcept(FE_DIVBYZERO))std::cout<<"    FE_DIVBYZERO raised\n";}

log1p(0) = 0Interest earned in 2 days on $100, compounded daily at 1%    on a 30/360 calendar = 0.00555563log(1+1e-16) = 0, but log1p(1e-16) = 1e-16log1p(-0) = -0log1p(+Inf) = inflog1p(-1) = -inf    errno == ERANGE: Result too large    FE_DIVBYZERO raised

[edit]See also

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