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           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
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DESCRIPTION

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

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

36       No errors occur.
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ATTRIBUTES

39       For  an  explanation  of  the  terms  used   in   this   section,   see
40       attributes(7).
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42       ┌──────────┬───────────────┬─────────┐
43       │Interface │ Attribute     │ Value   │
44       ├──────────┼───────────────┼─────────┤
45       │signbit() │ Thread safety │ MT-Safe │
46       └──────────┴───────────────┴─────────┘

CONFORMING TO

48       POSIX.1-2001,  POSIX.1-2008,  C99.  This function is defined in IEC 559
49       (and the appendix with recommended functions in IEEE 754/IEEE 854).
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COLOPHON

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56       description  of  the project, information about reporting bugs, and the
57       latest    version    of    this    page,    can     be     found     at
58       https://www.kernel.org/doc/man-pages/.
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62GNU                               2017-09-15                        SIGNBIT(3)