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Defined in header <math.h> | ||
float log2f(float arg); | (1) | (since C99) |
double log2(double arg); | (2) | (since C99) |
longdouble log2l(longdouble arg); | (3) | (since C99) |
Defined in header <tgmath.h> | ||
#define log2( arg ) | (4) | (since C99) |
arg has typelongdouble,log2l is called. Otherwise, ifarg has integer type or the typedouble,log2 is called. Otherwise,log2f is called.Contents |
| arg | - | floating point value |
If no errors occur, the base-2 logarithm ofarg (log2(arg) orlb(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.
Errors are reported as specified inmath_errhandling.
Domain error occurs ifarg is less than zero.
Pole error may occur ifarg is zero.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
For integerarg, the binary logarithm can be interpreted as the zero-based index of the most significant 1 bit in the input.
#include <stdio.h>#include <math.h>#include <float.h>#include <errno.h>#include <fenv.h>// #pragma STDC FENV_ACCESS ONint main(void){printf("log2(65536) = %f\n", log2(65536));printf("log2(0.125) = %f\n", log2(0.125));printf("log2(0x020f) = %f (highest set bit is in position 9)\n", log2(0x020f));printf("base-5 logarithm of 125 = %f\n", log2(125)/log2(5));// special valuesprintf("log2(1) = %f\n", log2(1));printf("log2(+Inf) = %f\n", log2(INFINITY));//error handlingerrno=0;feclearexcept(FE_ALL_EXCEPT);printf("log2(0) = %f\n", log2(0));if(errno==ERANGE)perror(" errno == ERANGE");if(fetestexcept(FE_DIVBYZERO))puts(" FE_DIVBYZERO raised");}
Possible output:
log2(65536) = 16.000000log2(0.125) = -3.000000log2(0x020f) = 9.041659 (highest set bit is in position 9)base-5 logarithm of 125 = 3.000000log2(1) = 0.000000log2(+Inf) = inflog2(0) = -inf errno == ERANGE: Numerical result out of range FE_DIVBYZERO raised
(C99)(C99) | computes natural (base-e) logarithm (\({\small \ln{x} }\)ln(x)) (function)[edit] |
(C99)(C99) | computes common (base-10) logarithm (\({\small \log_{10}{x} }\)log10(x)) (function)[edit] |
(C99)(C99)(C99) | computes natural (base-e) logarithm of 1 plus the given number (\({\small \ln{(1+x)} }\)ln(1+x)) (function)[edit] |
(C99)(C99)(C99) | computes2 raised to the given power (\({\small 2^x}\)2x) (function)[edit] |
C++ documentation forlog2 | |
