NAME

       isgreater,  isgreaterequal,  isless,  islessequal,  islessgreater, isunordered - floating-
       point relational tests without exception for NaN

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

       int isgreater(x, y);
       int isgreaterequal(x, y);
       int isless(x, y);
       int islessequal(x, y);
       int islessgreater(x, y);
       int isunordered(x, y);

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

           All functions described here:
               _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

       The normal relational operations (like <, "less than") fail if one of the operands is NaN.
       This will cause an exception.  To avoid this, C99 defines the macros listed below.

       These  macros are guaranteed to evaluate their arguments only once.  The arguments must be
       of real floating-point type (note: do not  pass  integer  values  as  arguments  to  these
       macros, since the arguments will not be promoted to real-floating types).

       isgreater()
              determines (x) > (y) without an exception if x or y is NaN.

       isgreaterequal()
              determines (x) >= (y) without an exception if x or y is NaN.

       isless()
              determines (x) < (y) without an exception if x or y is NaN.

       islessequal()
              determines (x) <= (y) without an exception if x or y is NaN.

       islessgreater()
              determines  (x) <  (y)  ||  (x)  > (y) without an exception if x or y is NaN.  This
              macro is not equivalent to x != y because that expression is true if x or y is NaN.

       isunordered()
              determines whether its arguments are unordered, that is, whether at  least  one  of
              the arguments is a NaN.

RETURN VALUE

       The  macros other than isunordered() return the result of the relational comparison; these
       macros return 0 if either argument is a NaN.

       isunordered() returns 1 if x or y is NaN and 0 otherwise.

ERRORS

       No errors occur.

ATTRIBUTES

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

       ┌───────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │Interface                                                      │ Attribute     │ Value   │
       ├───────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │isgreater(), isgreaterequal(), isless(), islessequal(),        │ Thread safety │ MT-Safe │
       │islessgreater(), isunordered()                                 │               │         │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       POSIX.1-2001, POSIX.1-2008, C99.

NOTES

       Not all hardware supports these functions, and where hardware support isn't provided, they
       will be emulated by macros.  This will result in a performance penalty.  Don't  use  these
       functions if NaN is of no concern for you.

SEE ALSO

       fpclassify(3), isnan(3)