FPCLASSIFY(3) Linux Programmer s Manual FPCLASSIFY(3)
NAME fpclassify, isfinite, isnormal, isnan, isinf - floating-point classifi- cation macros
SYNOPSIS #include <math.h>
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 nor- mal floating-point number.
The other macros provide a short answer to some standard questions.
isfinite(x) returns a non-zero value if (fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE)
isnormal(x) returns a non-zero value if (fpclassify(x) == FP_NORMAL)
isnan(x) returns a non-zero value if (fpclassify(x) == FP_NAN)
isinf(x) returns 1 if x is positive infinity, and -1 if x is nega- tive infinity.
CONFORMING TO C99, POSIX.1.
For isinf(), the standards merely say that the return value is non-zero if and only if the argument has an infinite value.
NOTES In glibc 2.01 and earlier, isinf() returns a non-zero 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)
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