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+.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
+.\" Distributed under GPL
+.\" 2002-07-27 Walter Harms
+.\" this was done with the help of the glibc manual
+.\"
+.TH ISGREATER 3  2002-07-27 "" "Linux Programmer's Manual"
+.SH NAME
+isgreater, isgreaterequal, isless, islessgreater, isunordered \- macros
+to test a relation
+.SH SYNOPSIS
+.nf
+.B #include <math.h>
+.sp
+.BI "int isgreater(x,y);
+.sp
+.BI "int isgreaterequal(x,y);
+.sp
+.BI "int isless(x,y);
+.sp
+.BI "int islessequal(x,y);
+.sp
+.BI "int islessgreater(x,y);
+.sp
+.BI "int isunordered(x,y);
+.fi
+.sp
+Link with \-lm.
+.SH DESCRIPTION
+The normal relation operations (like less) 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 operand can be of any real floating-point type.
+.TP
+isgreater()
+determines (x) > (y) without an exception if x or y is NaN.
+.TP
+isgreaterequal()
+determines (x) >= (y) without an exception if x or y is NaN.
+.TP 
+isless()
+determines (x) < (y) without an exception if x or y is NaN.
+.TP
+islessequal()
+determines (x) <= (y) without an exception if x or y is NaN.
+.TP
+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.
+.TP
+isunordered()
+is true if x or y is NaN and false otherwise.
+.SH NOTE
+Not all hardware supports these functions, and where it doesn't, they
+will be emulated by macros. This will give you a performance penalty.
+Don't use these functions if NaN is of no concern for you.
+.SH "CONFORMING TO"
+C99
+.SH "SEE ALSO"
+.BR fpclassify (3)
+.BR isnan(3)