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.TH NAN 2
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.SH NAME
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NaN, Inf, isNaN, isInf \- not-a-number and infinity functions
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.ta \w'\fLdouble 'u
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.B
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double	NaN(void)
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.PP
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.B
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double	Inf(int)
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.PP
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.B
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int	isNaN(double)
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.PP
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.B
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int	isInf(double, int)
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.SH DESCRIPTION
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The IEEE floating point standard defines values called
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`not-a-number' and positive and negative `infinity'.
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These values can be produced by such things as overflow
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and division by zero.
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Also, the library functions sometimes return them when
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the arguments are not in the domain, or the result is
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out of range.
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By default, manipulating these values may cause a floating point exception
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on some processors but
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.I setfcr
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(see
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.IR getfcr (2))
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can change that behavior.
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.PP
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.I NaN
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returns a double that is not-a-number.
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.I IsNaN
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returns true if its argument is not-a-number.
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.PP
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.IR Inf ( i )
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returns positive infinity if
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.I i
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is greater than or equal to zero,
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else negative infinity.
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.I IsInf
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returns true if its first argument is infinity
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with the same sign as the second argument.
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.SH SOURCE
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.B /sys/src/libc/port/nan.c
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.SH "SEE ALSO"
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.IR getfcr (2)