Section (3) logb
logb, logbf, logbl — get exponent of a floating-point value
||long double x
These functions extract the exponent from the internal
floating-point representation of
x and return it as a
floating-point value. The integer constant
FLT_RADIX, defined in
indicates the radix used for the system_zsingle_quotesz_s floating-point
x) is equal to
except that it is probably faster.
x is subnormal,
logb() returns the exponent
x would have if it
On success, these functions return the exponent of
x is a NaN, a
NaN is returned.
x is zero, then
a pole error occurs, and the functions return -
HUGE_VALF, or -
x is negative
infinity or positive infinity, then positive infinity is
See math_error(7) for information on how to determine whether an error has occurred when calling these functions.
The following errors can occur:
- Pole error:
A divide-by-zero floating-point exception (
FE_DIVBYZERO) is raised.
These functions do not set
For an explanation of the terms used in this section, see attributes(7).
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