signbit - test sign of a real floating-point number
signbit() is a generic macro which can work on all
real floating-point types. It returns a nonzero value if the value of
x has its sign bit set.
This is not the same as
x < 0.0, because IEEE 754
floating point allows zero to be signed. The comparison -0.0 <
0.0 is false, but
signbit(-0.0) will return a nonzero
NaNs and infinities have a sign bit.
The signbit() macro returns nonzero if the sign of
x is negative; otherwise it returns zero.
No errors occur.
POSIX.1-2001, POSIX.1-2008, C99. This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).
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