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Posted to dev@subversion.apache.org by kf...@collab.net on 2005/02/25 22:00:51 UTC
Re: svn commit: r13063 - trunk/subversion/libsvn_fs_base
brane@tigris.org writes:
> Log:
> Expand self-compressed deltas in BDB before combining. This is similar
> to the r13016 change in FSFS. It doesn't improve performance much by
> itself now that we use xdelta instead of vdelta in most cases, but
> opens the door for storing self-compressed deltas instead of fulltexts
> in BDB in the future.
>
> * subversion/libsvn_fs_base/reps-strings.c (compose_handler_baton):
> New member source_buf.
> (compose_handler): Expand self-compressed windows into source_buf.
> (rep_undeltify_range): Use the expanded fulltext provided by the
> combiner if available.
>
>
> --- trunk/subversion/libsvn_fs_base/reps-strings.c (original)
> +++ trunk/subversion/libsvn_fs_base/reps-strings.c Sat Feb 19 06:06:16 2005
> @@ -150,6 +150,11 @@
> svn_txdelta_window_t *window;
> apr_pool_t *window_pool;
>
> + /* If the incoming window was self-compressed, and the combined WINDOW
> + exists from previous iterations, SOURCE_BUF will point to the
> + expanded self-compressed window. */
> + char *source_buf;
> +
> /* The trail for this operation. WINDOW_POOL will be a child of
> TRAIL->pool. No allocations will be made from TRAIL->pool itself. */
> trail_t *trail;
Here source_buf is declared as 'char *', but...
> @@ -331,8 +364,7 @@
> }
> else
> {
> - static char empty_buf[] = "";
> - source_buf = empty_buf; /* Won't read anything from here. */
> + source_buf = ""; /* Won't read anything from here. */
> }
>
> if (offset > 0)
...here it is the assignee of a 'const char *' value, thus causing a
compiler warning.
Ordinarily, I wouldn't just cast over the situation, because of
writeable string concerns. But in this case, I cast it in 13159 in
the obvious way
source_buf = (char *) "";
because it looks like source_buf[0] would never be overwritten after
that point. If this was wrong, please let me know.
-Karl
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Re: svn commit: r13063 - trunk/subversion/libsvn_fs_base
Posted by Branko Čibej <br...@xbc.nu>.
Philip Martin wrote:
>How about something like this, no cast and no warnings:
>
>Index: subversion/libsvn_fs_base/reps-strings.c
>===================================================================
>--- subversion/libsvn_fs_base/reps-strings.c (revision 13157)
>+++ subversion/libsvn_fs_base/reps-strings.c (working copy)
>@@ -324,7 +324,8 @@
> do
> {
> struct compose_handler_baton cb = { 0 };
>- char *source_buf, *target_buf;
>+ const char *source_buf;
>+ char *target_buf;
>
>
[...]
After some discussion on IRC and some digging into the code, it turns
out that we can just set source_buf to NULL when we know it's not going
to be used. I'm on this now.
-- Brane
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Re: svn commit: r13063 - trunk/subversion/libsvn_fs_base
Posted by Philip Martin <ph...@codematters.co.uk>.
Branko Äibej <br...@xbc.nu> writes:
> kfogel@collab.net wrote:
>
>>brane@tigris.org writes:
>>
>>
>>>Log:
>>>Expand self-compressed deltas in BDB before combining. This is similar
>>>to the r13016 change in FSFS. It doesn't improve performance much by
>>>itself now that we use xdelta instead of vdelta in most cases, but
>>>opens the door for storing self-compressed deltas instead of fulltexts
>>>in BDB in the future.
>>>
>>>* subversion/libsvn_fs_base/reps-strings.c (compose_handler_baton):
>>> New member source_buf.
>>> (compose_handler): Expand self-compressed windows into source_buf.
>>> (rep_undeltify_range): Use the expanded fulltext provided by the
>>> combiner if available.
>>>
>>>
>>>--- trunk/subversion/libsvn_fs_base/reps-strings.c (original)
>>>+++ trunk/subversion/libsvn_fs_base/reps-strings.c Sat Feb 19 06:06:16 2005
>>>@@ -150,6 +150,11 @@
>>> svn_txdelta_window_t *window;
>>> apr_pool_t *window_pool;
>>> + /* If the incoming window was self-compressed, and the combined
>>> WINDOW
>>>+ exists from previous iterations, SOURCE_BUF will point to the
>>>+ expanded self-compressed window. */
>>>+ char *source_buf;
>>>+
>>> /* The trail for this operation. WINDOW_POOL will be a child of
>>> TRAIL->pool. No allocations will be made from TRAIL->pool itself. */
>>> trail_t *trail;
>>>
>>>
>>
>>Here source_buf is declared as 'char *', but...
>>
>>
>>
>>>@@ -331,8 +364,7 @@
>>> }
>>> else
>>> {
>>>- static char empty_buf[] = "";
>>>- source_buf = empty_buf; /* Won't read anything from here. */
>>>+ source_buf = ""; /* Won't read anything from here. */
>>> }
>>> if (offset > 0)
>>>
>>>
>>
>>...here it is the assignee of a 'const char *' value, thus causing a
>>compiler warning.
>>
>>
> String literals have type "char*" in C, not "const char*". The warning
> (turned on by -Wwrite-strings, IIRC) is possibly too much of a good
> think in this case.
However the "char*" type is a wart for backwards compatibility; string
literals should be treated as const, modifying one through a "char*"
pointer invokes undefined behaviour.
>>Ordinarily, I wouldn't just cast over the situation, because of
>>writeable string concerns. But in this case, I cast it in 13159 in
>>the obvious way
>>
>> source_buf = (char *) "";
>>
>>because it looks like source_buf[0] would never be overwritten after
>>that point. If this was wrong, please let me know.
>>
>>
> This cast is safe. But I'd rather put in the original code instead.
How about something like this, no cast and no warnings:
Index: subversion/libsvn_fs_base/reps-strings.c
===================================================================
--- subversion/libsvn_fs_base/reps-strings.c (revision 13157)
+++ subversion/libsvn_fs_base/reps-strings.c (working copy)
@@ -324,7 +324,8 @@
do
{
struct compose_handler_baton cb = { 0 };
- char *source_buf, *target_buf;
+ const char *source_buf;
+ char *target_buf;
apr_size_t target_len;
int cur_rep;
@@ -356,11 +357,13 @@
else if (fulltext && cb.window->sview_len > 0 && cb.window->src_ops > 0)
{
apr_size_t source_len = cb.window->sview_len;
- source_buf = apr_palloc (cb.window_pool, source_len);
+ char *source_buf_tmp = apr_palloc (cb.window_pool, source_len);
SVN_ERR (svn_fs_bdb__string_read
(fs, fulltext->contents.fulltext.string_key,
- source_buf, cb.window->sview_offset, &source_len, trail));
+ source_buf_tmp, cb.window->sview_offset, &source_len,
+ trail));
assert (source_len == cb.window->sview_len);
+ source_buf = source_buf_tmp;
}
else
{
--
Philip Martin
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Re: svn commit: r13063 - trunk/subversion/libsvn_fs_base
Posted by Branko Čibej <br...@xbc.nu>.
kfogel@collab.net wrote:
>brane@tigris.org writes:
>
>
>>Log:
>>Expand self-compressed deltas in BDB before combining. This is similar
>>to the r13016 change in FSFS. It doesn't improve performance much by
>>itself now that we use xdelta instead of vdelta in most cases, but
>>opens the door for storing self-compressed deltas instead of fulltexts
>>in BDB in the future.
>>
>>* subversion/libsvn_fs_base/reps-strings.c (compose_handler_baton):
>> New member source_buf.
>> (compose_handler): Expand self-compressed windows into source_buf.
>> (rep_undeltify_range): Use the expanded fulltext provided by the
>> combiner if available.
>>
>>
>>--- trunk/subversion/libsvn_fs_base/reps-strings.c (original)
>>+++ trunk/subversion/libsvn_fs_base/reps-strings.c Sat Feb 19 06:06:16 2005
>>@@ -150,6 +150,11 @@
>> svn_txdelta_window_t *window;
>> apr_pool_t *window_pool;
>>
>>+ /* If the incoming window was self-compressed, and the combined WINDOW
>>+ exists from previous iterations, SOURCE_BUF will point to the
>>+ expanded self-compressed window. */
>>+ char *source_buf;
>>+
>> /* The trail for this operation. WINDOW_POOL will be a child of
>> TRAIL->pool. No allocations will be made from TRAIL->pool itself. */
>> trail_t *trail;
>>
>>
>
>Here source_buf is declared as 'char *', but...
>
>
>
>>@@ -331,8 +364,7 @@
>> }
>> else
>> {
>>- static char empty_buf[] = "";
>>- source_buf = empty_buf; /* Won't read anything from here. */
>>+ source_buf = ""; /* Won't read anything from here. */
>> }
>>
>> if (offset > 0)
>>
>>
>
>...here it is the assignee of a 'const char *' value, thus causing a
>compiler warning.
>
>
String literals have type "char*" in C, not "const char*". The warning
(turned on by -Wwrite-strings, IIRC) is possibly too much of a good
think in this case.
>Ordinarily, I wouldn't just cast over the situation, because of
>writeable string concerns. But in this case, I cast it in 13159 in
>the obvious way
>
> source_buf = (char *) "";
>
>because it looks like source_buf[0] would never be overwritten after
>that point. If this was wrong, please let me know.
>
>
This cast is safe. But I'd rather put in the original code instead.
-- Brane
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