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Defined in header <cmath> | ||
| (1) | ||
float log2(float num); double log2(double num); | (until C++23) | |
/*floating-point-type*/ log2(/*floating-point-type*/ num); | (since C++23) (constexpr since C++26) | |
float log2f(float num); | (2) | (since C++11) (constexpr since C++26) |
longdouble log2l(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 log2( Integer num); | (A) | (constexpr since C++26) |
std::log2 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::log2 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 occur, the base-2 logarithm ofnum (log2(num) orlb(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.
Errors are reported as specified inmath_errhandling.
Domain error occurs ifnum is less than zero.
Pole error may occur ifnum is zero.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
For integernum, the binary logarithm can be interpreted as the zero-based index of the most significant 1 bit in the input.
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::log2(num) has the same effect asstd::log2(static_cast<double>(num)).
#include <cerrno>#include <cfenv>#include <cmath>#include <cstring>#include <iostream>// #pragma STDC FENV_ACCESS ON int main(){std::cout<<"log2(65536) = "<< std::log2(65536)<<'\n'<<"log2(0.125) = "<< std::log2(0.125)<<'\n'<<"log2(0x020f) = "<< std::log2(0x020f)<<" (highest set bit is in position 9)\n"<<"base-5 logarithm of 125 = "<< std::log2(125)/ std::log2(5)<<'\n'; // special valuesstd::cout<<"log2(1) = "<< std::log2(1)<<'\n'<<"log2(+Inf) = "<< std::log2(INFINITY)<<'\n'; // error handlingerrno=0;std::feclearexcept(FE_ALL_EXCEPT); std::cout<<"log2(0) = "<< std::log2(0)<<'\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:
log2(65536) = 16log2(0.125) = -3log2(0x020f) = 9.04166 (highest set bit is in position 9)base-5 logarithm of 125 = 3log2(1) = 0log2(+Inf) = inflog2(0) = -inf errno == ERANGE: Numerical result out of range 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) | natural logarithm (to basee) of1 plus the given number (\({\small\ln{(1+x)}}\)ln(1+x)) (function)[edit] |
(C++11)(C++11)(C++11) | returns2 raised to the given power (\({\small 2^x}\)2x) (function)[edit] |
C documentation forlog2 | |
