What is it, 2**48-2 signaling NaNs and 2**48 quiet NaNs? Is my quick count correct (in 64-bit)? Great opportunity for steganography, I reckon.
On Sun, Dec 29, 2019 at 11:51 PM Tim Peters <tim.pet...@gmail.com> wrote: > [David] > > Has anyone actually ever used those available bits for the zillions of > NaNs for > > anything good? > > Yes: in Python, many sample programs I've posted cleverly use NaN > bits to hide ASCII encodings of delightful puns ;-) > > Seriously? Not that I've seen. The _intent_ was that, e.g., quiet > NaNs could encode diagnostic information, such as the source code line > number of the operation that produced a qNaN. But I don't know that > anyone ever exploited that. > > Signaling NaNs were even more quixotic. For example, in theory, an > implementation _could_ reserve some range of sNaN bit patterns to mean > "the lower 20 bits are an index into a table of extended precision > values", and a trap handler could catch the signal when the sNaN was > used, and do extended-precision calculation in software, store the > result in the table, and return an sNaN containing the result's index > (or a regular double if the result fit in the format). > > In short, the kinds of things hardware designers think software would love > ;-) > -- Keeping medicines from the bloodstreams of the sick; food from the bellies of the hungry; books from the hands of the uneducated; technology from the underdeveloped; and putting advocates of freedom in prisons. Intellectual property is to the 21st century what the slave trade was to the 16th.
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