floating-point precision and zsh vs ksh93 and coreutils

[Vincent Lefevre <vincent@vinc17.net>]

For floating-point arithmetic evaluation, it appears that zsh uses the
"double" type while ksh93 and GNU coreutils both use the "long double"
type, which means incompatibility:

$ ksh93 -c '/usr/bin/printf "%a\n" $((1./3))'
0xa.aaaaaaaaaaaaa9ep-5
$ zsh -fc '/usr/bin/printf "%a\n" $((1./3))'
0xa.aaaaaaaaaaaa74ep-5

and

$ ksh93 -c '/usr/bin/printf "%a\n" $((43./2**22))'
0xa.cp-20
$ zsh -fc '/usr/bin/printf "%a\n" $((43./2**22))'
0xa.c0000000000025cp-20

In the second case, while the number is exactly representable
(and has the same value) in both double and long double, the
issue is visible because the number is passed with a decimal
representation, with enough decimal digits to read the result
with 53-bit precision in the zsh test.

Shouldn't zsh switch to long double?

Note: using printf from the GNU coreutils instead of the zsh printf
builtin is needed for %a support.

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)