How to test for +/- INFINITY, etc. in C with IEEE

[Doug Gwyn <gwyn>]

>    short pi[4] = {0x4008,0x1234,etc,etc};
>    double x, y;
>    x = y * *(double *)pi

Beware!  The alignment applied to (short) data may not be
sufficiently stringent for (double) data, so the result of
the (double *) typecast (assuming the compiler allows it)
may not be suitable for the address of an operand for a
floating-point instruction.  We have machines like that..

You can overcome this problem by proper use of a union.