[dmd-internals] Rare and pernicious bug in string append

[Andrei Alexandrescu]

Damn. Sorry.

Andrei

On 03/16/2010 10:14 AM, Steve Schveighoffer wrote:
> files?
>
> -Steve
>
>
>
> ----- Original Message ----
>> From: Andrei Alexandrescu<andrei at erdani.com>
>> To: Discuss the internals of DMD<dmd-internals at puremagic.com>; Walter Bright<walter at digitalmars.com>; Steven Schveighoffer<schveiguy at yahoo.com>; Sean Kelly<sean at invisibleduck.org>
>> Sent: Tue, March 16, 2010 11:04:49 AM
>> Subject: Rare and pernicious bug in string append
>>
>> This bug ruined a couple of workdays for me. (I'm using dmd 2.042 beta.) I'd
>> appreciate very much if people who know the innards of string append could look
>> into it at their earliest convenience. Currently the safe version is twice as
>> slow as the fast (buggy) version, so I'm looking at 8hrs instead of 4hrs for
>> completing an experiment against 5.75 million HTML files.
>
> The bug is
>> exceedingly rare. It occurs only once every few thousand HTML files. The failing
>> file occurs after 28,000 files have processed successfully.
>
> The code may
>> be further simplified, but not a lot. This is apparently a low-level bug because
>> small changes in the input or the code make the bug manifest differently or not
>> at all.
>
> To reproduce: copy untag.d and data.html to an empty directory.
>> Then compile untag:
>
> $ dmd untag
>
> To run untag without the bug,
>> run:
>
> ./untag --bug=0
>
> To run it with bug #1 related to string ~=,
>> run:
>
> ./untag --bug=1
>
> You will see:
>
> Invalid UTF sequence:
>> 255
>
> To run it with bug #2 related to string ~, run:
>
> ./untag
>> --bug=2
>
> You will see:
>
> Invalid UTF sequence: 252
>
> The three
>> programs should have identical semantics. Characters 255 and 252 are not present
>> in the input file.
>
>
> Andrei
>
>
>
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