Who can explain this strange behavior of typeset (-l) -En? For me it looks like
a bug.
> echo 2^69 | bc
590295810358705651712
> /bin/ksh -c 'typeset -l -E18 x;x=$(( pow(2,69) ));echo $x'
5.90295810358705652e+20
> /bin/ksh -c 'typeset -l -E19 x;x=$(( pow(2,69) ));echo $x'
5.90295810358705652e+20
> /bin/ksh -c 'typeset -l -E20 x;x=$(( pow(2,69) ));echo $x'
5.90295810358705652e+20
> /bin/ksh -c 'typeset -l -E21 x;x=$(( pow(2,69) ));echo $x'
590295810358705652
> echo 2^70 | bc
1180591620717411303424
> /bin/ksh -c 'typeset -l -E18 x;x=$(( pow(2,70) ));echo $x'
1.1805916207174113e+21
> /bin/ksh -c 'typeset -l -E19 x;x=$(( pow(2,70) ));echo $x'
1.1805916207174113e+21
> /bin/ksh -c 'typeset -l -E20 x;x=$(( pow(2,70) ));echo $x'
1.1805916207174113e+21
> /bin/ksh -c 'typeset -l -E21 x;x=$(( pow(2,70) ));echo $x'
1.1805916207174113e+21
> /bin/ksh -c 'typeset -l -E22 x;x=$(( pow(2,70) ));echo $x'
118059162071741130
> /bin/ksh -c 'typeset -E14 x;x=$(( pow(2,69) ));echo $x'
5.9029581035871e+20
> /bin/ksh -c 'typeset -E15 x;x=$(( pow(2,69) ));echo $x'
5.90295810358706e+20
> /bin/ksh -c 'typeset -E16 x;x=$(( pow(2,69) ));echo $x'
5.90295810358706e+20
> /bin/ksh -c 'typeset -E17 x;x=$(( pow(2,69) ));echo $x'
5.90295810358706e+20
> /bin/ksh -c 'typeset -E18 x;x=$(( pow(2,69) ));echo $x'
5.90295810358706e+20
> /bin/ksh -c 'typeset -E19 x;x=$(( pow(2,69) ));echo $x'
5.90295810358706e+20
> /bin/ksh -c 'typeset -E20 x;x=$(( pow(2,69) ));echo $x'
5.90295810358706e+20
> /bin/ksh -c 'typeset -E21 x;x=$(( pow(2,69) ));echo $x'
590295810358706
> /bin/ksh -c 'typeset -E15 x;x=$(( pow(2,70) ));echo $x'
1.18059162071741e+21
[...]
> /bin/ksh -c 'typeset -E21 x;x=$(( pow(2,70) ));echo $x'
1.18059162071741e+21
> /bin/ksh -c 'typeset -E22 x;x=$(( pow(2,70) ));echo $x'
118059162071741
I wonder what the precision of variables declared with typeset -E and typeset
-l -E is. In the above examples the significand appears to be 50 and 60 bit
resp., for 64 and 80 bit IEEE fp format I would expect 52 and 64 bit.
> echo $(( log2(590295810358706) ))
49.0684314306758268
> echo $(( log2(590295810358705652) ))
59.034215715337913
from the man page:
Arithmetic Evaluation.
[…] Evaluations are performed using double precision floating point
arithmetic
or long double precision floating point for systems that provide this
data type.
identical results for
version sh (AT&T Research) 93v- 2013-07-24
version sh (AT&T Research) 93u+ 2012-08-01
Linux, SLES11 SP2, Kernel 3.0.74-0.6.10-default
Best Regards
Axel Philipp
--
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