signbit(3)

1SIGNBIT(3)                 Linux Programmer's Manual                SIGNBIT(3)
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NAME

6       signbit - test sign of a real floating-point number
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SYNOPSIS

9       #include <math.h>
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11       int signbit(x);
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13       Link with -lm.
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15   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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17       signbit():
18           _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
19           _POSIX_C_SOURCE >= 200112L;
20           or cc -std=c99
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DESCRIPTION

23       signbit() is a generic macro which can work on all real  floating-point
24       types.   It  returns a nonzero value if the value of x has its sign bit
25       set.
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27       This is not the same as x < 0.0, because IEEE 754 floating point allows
28       zero  to  be  signed.   The  comparison  -0.0 < 0.0 is false, but sign‐
29       bit(-0.0) will return a nonzero value.
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31       NaNs and infinities have a sign bit.
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RETURN VALUE

34       The signbit() macro returns nonzero if the sign of x is negative;  oth‐
35       erwise it returns zero.
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ERRORS

38       No errors occur.
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ATTRIBUTES

41   Multithreading (see pthreads(7))
42       The signbit() macro is thread-safe.
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CONFORMING TO

45       C99, POSIX.1-2001.  This function is defined in IEC 559 (and the appen‐
46       dix with recommended functions in IEEE 754/IEEE 854).
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COLOPHON

52       This page is part of release 3.53 of the Linux  man-pages  project.   A
53       description  of  the project, and information about reporting bugs, can
54       be found at http://www.kernel.org/doc/man-pages/.
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58GNU                               2013-07-04                        SIGNBIT(3)