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In the 1970s, Grace Hopper, also known as "Grandma COBOL", pushed for the Defense Department to replace large, centralized systems with networks of small, distributed computers.
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isnan(3m) [opensolaris man page]

isnan(3M)						  Mathematical Library Functions						 isnan(3M)

NAME
isnan - test for NaN SYNOPSIS
cc [ flag... ] file... -lm [ library... ] #include <math.h> int isnan(double x); c99 [ flag... ] file... -lm [ library... ] #include <math.h> int isnan(real--floating x); DESCRIPTION
In C90 mode, the isnan() function tests whether x is NaN. In C99 mode, the isnan() macro determines whether its argument value is NaN. First, an argument represented in a format wider than its semantic type is converted to its semantic type. The determination is then based on the type of the argument. RETURN VALUES
Both the isnan() function and macro return non-zero if and only if x is NaN. ERRORS
No errors are defined. WARNINGS
In C99 mode, the practice of explicitly supplying a prototype for isnan() after the line #include <math.h> is obsolete and will no longer work. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
fpclassify(3M), isfinite(3M), isinf(3M), isnormal(3M), math.h(3HEAD), signbit(3M), attributes(5), standards(5) SunOS 5.11 12 Jul 2006 isnan(3M)

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FPCLASSIFY(3)						     Linux Programmer's Manual						     FPCLASSIFY(3)

NAME
fpclassify, isfinite, isnormal, isnan, isinf - floating-point classification macros SYNOPSIS
#include <math.h> int fpclassify(x); int isfinite(x); int isnormal(x); int isnan(x); int isinf(x); Link with -lm. Feature Test Macro Requirements for glibc (see feature_test_macros(7)): fpclassify(), isfinite(), isnormal(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99 isnan(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE; or cc -std=c99 isinf(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99 DESCRIPTION
Floating point numbers can have special values, such as infinite or NaN. With the macro fpclassify(x) you can find out what type x is. The macro takes any floating-point expression as argument. The result is one of the following values: FP_NAN x is "Not a Number". FP_INFINITE x is either positive infinity or negative infinity. FP_ZERO x is zero. FP_SUBNORMAL x is too small to be represented in normalized format. FP_NORMAL if nothing of the above is correct then it must be a normal floating-point number. The other macros provide a short answer to some standard questions. isfinite(x) returns a nonzero value if (fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE) isnormal(x) returns a nonzero value if (fpclassify(x) == FP_NORMAL) isnan(x) returns a nonzero value if (fpclassify(x) == FP_NAN) isinf(x) returns 1 if x is positive infinity, and -1 if x is negative infinity. CONFORMING TO
C99, POSIX.1. For isinf(), the standards merely say that the return value is nonzero if and only if the argument has an infinite value. NOTES
In glibc 2.01 and earlier, isinf() returns a nonzero value (actually: 1) if x is positive infinity or negative infinity. (This is all that C99 requires.) SEE ALSO
finite(3), INFINITY(3), isgreater(3), signbit(3) COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. 2008-08-07 FPCLASSIFY(3)

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