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 these macros. The macros are guaranteed to evaluate their
operands only once. The operands can be of any real floating-point
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.
determines whether its arguments are unordered, that is, whether
at least one of the arguments is a 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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