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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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signbit(3) Library Functions Manual signbit(3)
signbit - test sign of a real floating-point number
Math library (libm, -lm)
#include <math.h>
int signbit(x);
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 │
└──────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
POSIX.1-2001, C99.
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 the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
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⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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Linux man-pages 6.10 2024-07-23 signbit(3)
Pages that refer to this page: copysign(3), fpclassify(3)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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