gab-buffer issue

gab-buffer issue

[Mario Domenech Goulart]

Hi,

I'm using the CHICKEN port [1] of Guile's gap-buffer implementation and
noticed a strange behavior in a simple test case.  I can reproduce that
behavior on Guile 2.0.5 and 2.0.9, but not on Guile 2.0.11.

[1] http://wiki.call-cc.org/eggref/4/gap-buffer

Here's the test case:

$ cat guile-gap-buffer.scm
(use-modules (ice-9 gap-buffer))

(define buffer (make-gap-buffer ""))

(define data
  "aaaaa\nbbbbb\nccccc\nddddd\neeeee\nffff\nggggg\nhhhhh\niiiii\njjjjj\nkkkkk\nlllll\n")

(gb-insert-string! buffer data)

(display "Before goto-char: ")
(newline)
(display (gb->string buffer))
(newline)

(gb-goto-char buffer 1)

(display "After goto-char:")
(newline)
(display (gb->string buffer))
(newline)

$ guile -s guile-gap-buffer.scm
Before goto-char: 
aaaaa
bbbbb
ccccc
ddddd
eeeee
ffff
ggggg
hhhhh
iiiii
jjjjj
kkkkk
lllll

After goto-char:
aaaaa
bbbbb
ccccc
ddddd
eeeee
ffff
ggggg
hhhhh
iiiii
jjjjaaaaa
bbbbb
cc

$ guile --version
guile (GNU Guile) 2.0.5-deb+1-3
Copyright (C) 2011 Free Software Foundation, Inc.

License LGPLv3+: GNU LGPL 3 or later
<http://gnu.org/licenses/lgpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.


With Guile 2.0.11 I get the expected behavior:

$ ~/local/guile-2.0.11/bin/guile -s guile-gap-buffer.scm
Before goto-char: 
aaaaa
bbbbb
ccccc
ddddd
eeeee
ffff
ggggg
hhhhh
iiiii
jjjjj
kkkkk
lllll

After goto-char:
aaaaa
bbbbb
ccccc
ddddd
eeeee
ffff
ggggg
hhhhh
iiiii
jjjjj
kkkkk
lllll


Do you know what may be causing the behavior observed with CHICKEN and
older Guile versions?

Best wishes.
Mario
-- 
http://parenteses.org/mario

Re: gab-buffer issue

[Mark H Weaver]

Hi Mario,

Mario Domenech Goulart <mario.goulart@gmail.com> writes:
> I'm using the CHICKEN port [1] of Guile's gap-buffer implementation and
> noticed a strange behavior in a simple test case.  I can reproduce that
> behavior on Guile 2.0.5 and 2.0.9, but not on Guile 2.0.11.

In Guile versions 2.0.0 - 2.0.9, there was a bug in 'string-copy!' such
that it did not work properly when the source and destination ranges
overlapped.  The characters were always copied starting from the lowest
index, so it would fail when moving a block of characters to higher
indices.  'string-copy!' is used by 'substring-move!', which in turn is
used by 'gb-goto-char'.

The bug was introduced in f846bd1a8f0e0d366fb8bb6944598641bc3dd246 when
the SRFI-13 functions were updated for Unicode, and fixed in
793e8a9317d24298c82389bdf86b8ca17b4ee2f0.

    Regards,
      Mark

Re: gab-buffer issue

[Mario Domenech Goulart]

On Fri, 27 Jun 2014 10:06:48 -0400 Mark H Weaver <mhw@netris.org> wrote:

> Mario Domenech Goulart <mario.goulart@gmail.com> writes:
>> I'm using the CHICKEN port [1] of Guile's gap-buffer implementation and
>> noticed a strange behavior in a simple test case.  I can reproduce that
>> behavior on Guile 2.0.5 and 2.0.9, but not on Guile 2.0.11.
>
> In Guile versions 2.0.0 - 2.0.9, there was a bug in 'string-copy!' such
> that it did not work properly when the source and destination ranges
> overlapped.  The characters were always copied starting from the lowest
> index, so it would fail when moving a block of characters to higher
> indices.  'string-copy!' is used by 'substring-move!', which in turn is
> used by 'gb-goto-char'.
>
> The bug was introduced in f846bd1a8f0e0d366fb8bb6944598641bc3dd246 when
> the SRFI-13 functions were updated for Unicode, and fixed in
> 793e8a9317d24298c82389bdf86b8ca17b4ee2f0.

Many thanks for the detailed and straight-to-the-point info, Mark.  It
looks like CHICKEN's string-copy! is buggy.  I've locally applied a fix
to it and can confirm it fixes the gap-buffer issue.

Best wishes.
Mario
-- 
http://parenteses.org/mario