I think a perlbug report should be filed for this.

Thing is, there is not a lot that Perl can do about it, as it is the default (and preferred) behaviour for floating point.

In the code below, the bit pattern 0x0x7ff0000000000001 displays as SNaN, only when nothing has caused the value to be loaded into a floating point register.

As soon as the value is loaded into an FP register, it gets silently converted to a QNan; and if the operation causes the result to be stored back to memory, the bit pattern will have been changed to a QNaN pattern.

And, I've tried every combination of Exception Mask bits in the FP control word to change that behaviour and nothing does. I do not see how Perl could change that behaviour outside of emulating FP in software?

Note how both the displayed representation of the value and the bit pattern change as soon as *any* floating point operation is performed on the value:

#include <stdio.h>
#include <float.h>

typedef union {
    double  d;
    __int64 i;
} BITS64;

int main( int argc, char ** argv ) {
    BITS64 x;

    __try {
        _controlfp( _EM_INVALID|_EM_DENORMAL|_EM_ZERODIVIDE|_EM_OVERFL
+OW|_EM_UNDERFLOW|_EM_INEXACT, _MCW_EM );

        x.i = 0x7ff0000000000001;

        printf( "as int: %I64u\n", x.i );
        printf( "as dbl: %f\n",    x.d );

        x.d += 0.0;

        printf( "as dbl: %f\n",    x.d );
        printf( "as int: %I64u\n", x.i );
    }
    __except( 1 ) {
        fprintf( stderr, "Exception caught!\n" );
        exit( -1 );
    }
    return 0;
}

/*

C:\test>junk.exe
as int: 9218868437227405313
as dbl: 1.#SNAN0
as dbl: 1.#QNAN0
as int: 9221120237041090561

*/
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