GNU/Linux man pages
Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :
GNU/Linux |
CentOS 5.2 |
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logb(3) |
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logb, logbf, logbl − get exponent of a floating point value
#include <math.h>
double
logb(double x);
float logbf(float x);
long double logbl(long double x);
Link with −lm.
These functions extract the exponent of x and return it as a floating-point value. If FLT_RADIX is two, logb(x) is equal to floor(log2(x)), except it’s probably faster.
If x is de-normalized, logb() returns the exponent x would have if it were normalized.
If x is zero, −HUGE_VAL (resp. −HUGE_VALF, −HUGE_VALL) is returned, and a pole error occurs. If x is infinite, plus infinity is returned. If x is NaN, NaN is returned.
In order to check for errors, set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
If an error occurs and (math_errhandling & MATH_ERRNO) is non-zero, then errno is set to ERANGE. If an error occurs and (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception is raised.
A pole error occurs when x is zero.
The logb() function occurs in 4.3BSD.
C99
log(3), ilogb(3)
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logb(3) | |