SIGNBIT(3) libc math functions SIGNBIT(3)
signbit - test sign of a real floating point number
int signbit (X);
`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
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 value.
This function is defined in IEC 559 (and the appendix with recommended
functions in IEEE 754/IEEE 854).
GNU 2002-08-10 SIGNBIT(3)