isunordered - floating-point relational tests without exception for NaN
int isgreater(x, y);
int isgreaterequal(x, y);
int isless(x, y);
int islessequal(x, y);
int islessgreater(x, y);
int isunordered(x, y);
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
All functions described here:
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
The normal relation operations (like <, "less than") will 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 inte-
ger values as arguments to these macros, since the arguments will not
be promoted to real-floating types).
determines (x) > (y) without an exception if x or y is NaN.
determines (x) >= (y) without an exception if x or y is NaN.
determines (x) < (y) without an exception if x or y is NaN.
determines (x) <= (y) without an exception if x or y is NaN.
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.
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
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