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Postings from December 2013
On Thu, Oct 31, 2013 at 07:59:37AM -0700, via RT wrote:
> Compare the following two commands. The first one thinks the
> number is zero, the second one works fine. The whole difference
> is an extra "0" in the mantissa.
>
> # echo 0.1530e-305 | perl -e '$v = <STDIN>; print "v=", $v + 0, "\n";'
> v=0
> # echo 0.153e-305 | perl -e '$v = <STDIN>; print "v=", $v + 0, "\n";'
> v=1.53e-306
>
> The above is not supposed to underflow; there are still a couple of orders
> of magnitude left:
> # echo 0.1e-307 | perl -e '$v = <STDIN>; print "v=", $v + 0, "\n";'
> v=9.99999999999999e-309
>
> Observed with 5.16.0
> Not observed with 5.6.1
> Not observed with 5.12.4
>
> Observed with OpenSuSE build (5.16.0).
I've (hopefully) fixed it with the following commit, which I've just
pushed for smoking:
commit 07079ca1f145dc1ad3cfd0d9fa30d08871c79636
Author: David Mitchell <davem@iabyn.com>
AuthorDate: Mon Dec 2 15:04:49 2013 +0000
Commit: David Mitchell <davem@iabyn.com>
CommitDate: Mon Dec 2 15:04:49 2013 +0000
[perl #120426] atof() errors with trailing 0's
For small numbers, trailing zeros in the fractional part of a
floating-point literal could cause rounding to zero.
From the bug report:
$ echo 0.1530e-305 | perl -e '$v = <STDIN>; print "v=", $v + 0, "\n";'
v=0
$ echo 0.153e-305 | perl -e '$v = <STDIN>; print "v=", $v + 0, "\n";'
v=1.53e-306
I fixed this by stopping the processing of the integer or fractional
component once its been detected that only zeroes are left (with a
suitable adjustment of the exponent).
--
print+qq&$}$"$/$s$,$a$d$g$s$@$.$q$,$:$.$q$^$,$@$a$~$;$.$q$m&if+map{m,^\d{0\,},,${$::{$'}}=chr($"+=$&||1)}q&10m22,42}6:17a2~2.3@3;^2dg3q/s"&=~m*\d\*.*g
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