fpclassify, isfinite, isnormal, isnan, isinf - floating-point classification macros

```
#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():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

isnan():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

isinf():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

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.

For an explanation of the terms used in this section, see attributes(7).

Interface | Attribute | Value |

fpclassify(), isfinite(), isnormal(), isnan(), isinf() | Thread safety | MT-Safe |

POSIX.1-2001, POSIX.1-2008, C99.

For isinf(), the standards merely say that the return value is nonzero if and only if the argument has an infinite value.

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.)

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