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### 1.24 `isnan`, `isnanf`, `isinf`, `isinff`, `finite`, `finitef`—test for exceptional numbers

Synopsis

         #include <ieeefp.h>
         int isnan(double arg);
         int isinf(double arg);
         int finite(double arg);
         int isnanf(float arg);
         int isinff(float arg);
         int finitef(float arg);

Description
These functions provide information on the floating-point argument supplied.

There are five major number formats:

`zero`
  A number which contains all zero bits.
`subnormal`
  A number with a zero exponent but a nonzero fraction.
`normal`
  A number with an exponent and a fraction.
`infinity`
  A number with an all 1's exponent and a zero fraction.
`NAN`
  A number with an all 1's exponent and a nonzero fraction.

`isnan` returns 1 if the argument is a nan. `isinf` returns 1 if the argument is infinity. `finite` returns 1 if the argument is zero, subnormal or normal. The `isnanf`, `isinff` and `finitef` functions perform the same operations as their `isnan`, `isinf` and `finite` counterparts, but on single-precision floating-point numbers.

It should be noted that the C99 standard dictates that `isnan` and `isinf` are macros that operate on multiple types of floating-point. The SUSv2 standard declares `isnan` as a function taking double. Newlib has decided to declare them both as macros in math.h and as functions in ieeefp.h.