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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | SEE ALSO | COLOPHON |
SIGNBIT(3) Linux Programmer's Manual SIGNBIT(3)
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():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
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.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────┼───────────────┼─────────┤
│signbit() │ Thread safety │ MT-Safe │
└──────────┴───────────────┴─────────┘
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).
copysign(3)
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GNU 2016-03-15 SIGNBIT(3)
Pages that refer to this page: copysign(3), fpclassify(3)