On Sat, Jan 08, 2022 at 12:00:38PM +0100, Jakub Jelinek via Gcc-patches wrote:
> And IMHO the default like for byte-swapping should be the native
> format, i.e. the one the program actually used.
One reason for that is that neither conversion is lossless, neither format
is a subset or superset of the other. Yes, IEEE quad has both much bigger
exponent range (-16382..16383 vs. -1022..1023) and slightly bigger fixed
precision (113 vs. 106 bits).
But IBM extended has that weirdo numerically awful flexible precision where
certain numbers can have much bigger precision than those 106 bits, up to
2048+52 or so. So there is rounding in both directions.
So, after distros switch to -mabi=ieeelongdouble by default or when people
use -mabi=ieeelongdouble on their programs, they'd better store that format
into data files by default, without the need of some magic CONVERT= options,
env vars or command line options. Only in the case where they need to
interact with -mabi=ibmlongdouble environments, they need to take some
action.
Jakub
