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(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99
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DESCRIPTION

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

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

35       No errors occur.
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CONFORMING TO

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

42       copysign(3)
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COLOPHON

45       This  page  is  part of release 3.25 of the Linux man-pages project.  A
46       description of the project, and information about reporting  bugs,  can
47       be found at http://www.kernel.org/doc/man-pages/.
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51GNU                               2008-08-05                        SIGNBIT(3)
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