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Defined in header <cmath> | ||
| (1) | ||
float log1p(float num); double log1p(double num); | (until C++23) | |
/*floating-point-type*/ log1p(/*floating-point-type*/ num); | (since C++23) (constexpr since C++26) | |
float log1pf(float num); | (2) | (since C++11) (constexpr since C++26) |
longdouble log1pl(longdouble num); | (3) | (since C++11) (constexpr since C++26) |
SIMD overload(since C++26) | ||
Defined in header <simd> | ||
template</*math-floating-point*/ V> constexpr/*deduced-simd-t*/<V> | (S) | (since C++26) |
Additional overloads(since C++11) | ||
Defined in header <cmath> | ||
template<class Integer> double log1p( Integer num); | (A) | (constexpr since C++26) |
std::log1p for all cv-unqualified floating-point types as the type of the parameter.(since C++23)S) The SIMD overload performs an element-wise std::log1p onv_num.
| (since C++26) |
A) Additional overloads are provided for all integer types, which are treated asdouble. | (since C++11) |
Contents |
| num | - | floating-point or integer 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.
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),
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)).
#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";}
Possible output:
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
(C++11)(C++11) | computes natural (basee) logarithm (\({\small\ln{x}}\)ln(x)) (function)[edit] |
(C++11)(C++11) | computes common (base10) logarithm (\({\small\log_{10}{x}}\)log10(x)) (function)[edit] |
(C++11)(C++11)(C++11) | base2 logarithm of the given number (\({\small\log_{2}{x}}\)log2(x)) (function)[edit] |
(C++11)(C++11)(C++11) | returnse raised to the given power, minus1 (\({\small e^x-1}\)ex-1) (function)[edit] |
C documentation forlog1p | |
