Steven D'Aprano <st...@pearwood.info>: > Nevertheless, it's well known (in the sense that "everybody knows") > that Python floats are equivalent to C 64-bit IEEE-754 doubles. How > safe is that assumption?
You'd need to have it in writing, wouldn't you? The only spec I know of promises no such thing: Floating point numbers are usually implemented using double in C; information about the precision and internal representation of floating point numbers for the machine on which your program is running is available in sys.float_info. <URL: https://docs.python.org/3/library/stdtypes.html#typesnumeric> > As an optimization, I want to write: > > def func(n): > if n <= 2**53: > # use the floating point fast implementation > else: > # fall back on the slower, but exact, int algorithm > > [...] > > But I wonder whether I need to write this instead? > > def func(n): > if n <= 2**sys.float_info.mant_dig: > # ...float > else: > # ...int > > I don't suppose it really makes any difference performance-wise, but I > can't help but wonder if it is really necessary. If > sys.float_info.mant_dig is guaranteed to always be 53, why not just > write 53? Mainly because 2**sys.float_info.mant_dig looks much better than 2**53 Marko -- https://mail.python.org/mailman/listinfo/python-list
