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

NAME

     signbit - test sign of a real floating-point number

SYNOPSIS

     #include <math.h>

     int signbit(x);

     Link with -lm.

 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

     signbit():
         _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

     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  sign-
     bit(-0.0) will return a nonzero value.

     NaNs and infinities have a sign bit.

RETURN VALUE

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

ERRORS

     No errors occur.

ATTRIBUTES

     For  an  explanation  of  the  terms  used   in   this   section,   see
     attributes(7).

     +----------+---------------+---------+
     |Interface | Attribute     | Value   |
     +----------+---------------+---------+
     |signbit() | Thread safety | MT-Safe |
     +----------+---------------+---------+

CONFORMING TO

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

SEE ALSO

     copysign(3)

COLOPHON

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     https://www.kernel.org/doc/man-pages/.

GNU 2017-09-15 SIGNBIT(3)