Arithmetic operations turn signaling NaNs into quiet NaNs (on the x86, by writing a one into bit 22 of a float).  The mere act of copying a floating-point value can also trigger this conversion, including a load to or store from the FPU.  In particular, the copying of a function return value may be triggering the conversion.

[...] on some processors it may just be impossible to pass a signaling NaN into floatToRawIntBits (using intBitsToFloat is the only way to possibly create a signaling NaN in Java).

Some processors do not perform the NaN conversion on a copy; for example, the test program works as expected on SPARC but not on x86.  The analogous problem also occurs for double values on the x86.  I'll consult some C gurus but I believe the issue may be inherent in the C calling conventions.  If so, this bug will be 'closed - will not fix' but I will add a note about this possibility in the JavaDoc.

Preserving the NaN flavor is not necessary for floating-point computations in Java; Java hides the functional difference between signaling and quiet NaNs (namely that the former signal the IEEE 754 invalid condition).

The nio classes can be used to change endianess of buffers.

15.21.1 Numerical Equality Operators == and !=

If the operands of an equality operator are both of numeric type, or one is of numeric type and the other is convertible (§5.1.8) to numeric type, binary numeric promotion is performed on the operands (§5.6.2). If the promoted type of the operands is int or long, then an integer equality test is performed; if the promoted type is float or double, then a floating-point equality test is performed.

Note that binary numeric promotion performs value set conversion (§5.1.13) and unboxing conversion (§5.1.8). Comparison is carried out accurately on floating-point values, no matter what value sets their representing values were drawn from.

Floating-point equality testing is performed in accordance with the rules of the IEEE 754 standard:

• If either operand is NaN, then the result of == is false but the result of != is true. Indeed, the test x!=x is true if and only if the value of x is NaN. (The methods Float.isNaN and Double.isNaN may also be used to test whether a value is NaN.)
• Positive zero and negative zero are considered equal. Therefore, -0.0==0.0 is true, for example.
• Otherwise, two distinct floating-point values are considered unequal by the equality operators. In particular, there is one value representing positive infinity and one value representing negative infinity; each compares equal only to itself, and each compares unequal to all other values.

Subject to these considerations for floating-point numbers, the following rules then hold for integer operands or for floating-point operands other than NaN:

• The value produced by the == operator is true if the value of the left-hand operand is equal to the value of the right-hand operand; otherwise, the result is false.
• The value produced by the != operator is true if the value of the left-hand operand is not equal to the value of the right-hand operand; otherwise, the result is false.
  

I have been since seventeen a shipwreck balladeer  
Tragedy and misery are what makes my career  
Watery graves are my stock and trade, but it's getting harder  
For all the boats that now do float are returning safely to the harbour  
 
There hasn't been a shipwreck scene since 1965  
And I find I cry each time a crew returns alive  
I only cheer when gales appear and threaten fresh disaster  
They pass by, the boat survives, only my career's in tatters  
 
They're building ships too good today, and I'm the one who suffers  
They don't get rent from aft to stern and their halls never rupture  
Not dashed on rocks and never tossed to heaven on a wave  
You may think it well and good but my livelihood sails away  
 
There once were found, twenty in town, who wrote about shipwrecks  
When boats sank lots, just like rocks, 'twas good as it gets  
But the golden ages passed away and I'm barely survivin'  
The balladeers are dead I fear and workin' in advertisin'  
 
They're building ships too good today and it's hurtin' me  
Why can't even one poor soul fall into the dark sea  
And be ripped apart by hungry sharks in a bloody spree  
You may think it well and good, but my livelihood sails away  
 
Oh the only tragedy left to sing about is me  
 
That government bastard's been sent to take my job from me  
That inspector's making sure the ships are seaworthy  
He can try, no way will I ever give up hope  
When he went by, I did pry a big hole in his boat  
 
They're building ships too good today, so I helped one along  
How sweet it is to once again hear the tortured song  
Of a man afloat a sinking boat, who knows he will die today  
You might think it bad not good, but my livelihood's here to stay  
It's here to staaaaaaaaaaaaaaaaaaaaaay