SIGNBIT(3) manual page
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signbit - test sign of a real floating-point number
#include
<math.h>
int signbit(x);
Link with -lm.
Feature Test Macro Requirements for
glibc (see feature_test_macros(7)
):
signbit():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE
|| _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
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 value.
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.
The signbit() macro is thread-safe.
C99, POSIX.1-2001.
This function is defined in IEC 559 (and the appendix with recommended
functions in IEEE 754/IEEE 854).
copysign(3)
This page is
part of release 3.78 of the Linux man-pages project. A description of the
project, information about reporting bugs, and the latest version of this
page, can be found at http://www.kernel.org/doc/man-pages/.
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