libm.info: isnan

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`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'
     Is used to represent  number with a zero exponent, but a non zero
     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 non zero 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' perform the
same operations as their `isnan', `isinf' and `finite' counterparts,
but on single precision floating point numbers.