signbit(3)

1signbit(3)                 Library Functions Manual                 signbit(3)
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NAME

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

9       Math library (libm, -lm)
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SYNOPSIS

12       #include <math.h>
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14       int signbit(x);
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16   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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18       signbit():
19           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
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DESCRIPTION

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

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

37       No errors occur.
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ATTRIBUTES

40       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
41       tributes(7).
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43       ┌────────────────────────────────────────────┬───────────────┬─────────┐
44       │Interface                                   │ Attribute     │ Value   │
45       ├────────────────────────────────────────────┼───────────────┼─────────┤
46       │signbit()                                   │ Thread safety │ MT-Safe │
47       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

50       C11, POSIX.1-2008.
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HISTORY

53       POSIX.1-2001, C99.
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55       This  function is defined in IEC 559 (and the appendix with recommended
56       functions in IEEE 754/IEEE 854).
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