by my reading of Wikipedia, underflow ... is also an exception in IEEE 754. So it, too, pertains to "a value beyond the capabilities of the binary format to represent".

Maybe we'll see you referring to an "erroneous zero" at some time in the future ;-)

Hm. Did you ever see Edward Woodward in The Wicker Man? That was a bigger straw man, but not by much :)

An "erroneous zero"? No. A value of zero erroneously produced when underflow occurs, yes.

And if you override the run-time's dubious default setting of 'ignoring floating point exceptions', it can even be detected and handled:

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <float.h>
#include <excpt.h>

int main( int argc, char **argv ) {
    unsigned int  u = _controlfp(0, 0);
    double x = 0.5e-323, y = 0.5e-323;

    printf( "x contains: %g before dividing by 2\n", x );
    x /= 2;
    printf( "x now contains: %g\n", x );

    u = u & ~_EM_UNDERFLOW;
    _controlfp(u, _MCW_EM);

    printf( "\ny contains: %g before dividing by 2\n", y );
    __try {
        y /= 2;
    }
    __except( EXCEPTION_EXECUTE_HANDLER ) {
        printf( "Floating point underflow exception occurred\n");
    }
    printf( "y now contains: %g\n", y );
    return 0;
}
[download]

So whilst the value zero isn't erroneous; a variable can acquire the value zero erroneously:

C:\test>intOverflow.exe
x contains: 4.94066e-324 before dividing by 2
x now contains: 0

y contains: 4.94066e-324 before dividing by 2
Floating point underflow exception occurred
y now contains: 4.94066e-324
[download]

Is this going anywhere?