Mark Dickinson <dicki...@gmail.com> added the comment:
float_info.rounds is a bit of an odd fish, and I think it was probably a
mistake to include it in sys.float_info in the first place.
All the other float_info fields relate to parameters of the floating-point
format, which is fixed, useful information. In contrast, float_info.rounds
gives information about the current FPU settings, which are variable.
Moreover, it doesn't do that very well: all it does is give information about
the FPU settings at the time that Python was compiled, which isn't really very
helpful (and perhaps not even that: it reports the value of FLT_ROUNDS, which
may not even reflect those FPU settings accurately). I wouldn't mind seeing
this field fade quietly into obscurity.
FWIW, the value is taken from C's FLT_ROUNDS, and its interpretation is
*supposed* to be the following (C99 5.2.4.2.2, para 7):
-1: The compiler was unable to determine rounding mode.
0: Round towards zero.
1: Round to nearest (this is the most likely value for
float_info.rounds on common platforms).
2: Round towards positive infinity
3: Round towards negative infinity.
----------
nosy: +mark.dickinson
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<http://bugs.python.org/issue12245>
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