logb - radix-independent exponent
#include <math.h> double logb(double x);
The logb() function computes the exponent of x, which is the integral part of logr | x | , as a signed floating point value, for non-zero x, where r is the radix of the machine's floating-point arithmetic.
Upon successful completion, logb() returns the exponent of x.If x is 0.0, logb() returns -HUGE_VAL and sets errno to [EDOM].
If x is ±Inf, logb() returns +Inf.
If x is NaN, logb() returns NaN and may set errno to [EDOM].
The logb() function will fail if:
- [EDOM]
- The x argument is 0.0.
The logb() function may fail if:
- [EDOM]
- The x argument is NaN.
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ilogb(), <math.h>.