path: root/vcs-svn/sliding_window.h
diff options
authorJonathan Nieder <>2011-01-03 03:54:58 (GMT)
committerJonathan Nieder <>2011-03-28 01:23:32 (GMT)
commit9d2f5ddfe56fcc228a36dd079f0897e0f474eb4e (patch)
treeac08de7bff81eb1d33395d8cb1b2998a60475afb /vcs-svn/sliding_window.h
parent3371f9b3fb13a508c447e484618b9b5e2b9e45a7 (diff)
vcs-svn: learn to maintain a sliding view of a file
Each section of a Subversion-format delta only requires examining (and keeping in random-access memory) a small portion of the preimage. At any moment, this portion starts at a certain file offset and has a well-defined length, and as the delta is applied, the portion advances from the beginning to the end of the preimage. Add a move_window function to keep track of this view into the preimage. You can use it like this: buffer_init(f, NULL); struct sliding_view window = SLIDING_VIEW_INIT(f); move_window(&window, 3, 7); /* (1) */ move_window(&window, 5, 5); /* (2) */ move_window(&window, 12, 2); /* (3) */ strbuf_release(&window.buf); buffer_deinit(f); The data structure is called sliding_view instead of _window to prevent confusion with svndiff0 Windows. In this example, (1) reads 10 bytes and discards the first 3; (2) discards the first 2, which are not needed any more; and (3) skips 2 bytes and reads 2 new bytes to work with. When move_window returns, the file position indicator is at position window->off + window->width and the data from positions window->off to the current file position are stored in window->buf. This function performs only sequential access from the input file and never seeks, so it can be safely used on pipes and sockets. On end-of-file, move_window silently reads less than the caller requested. On other errors, it prints a message and returns -1. Helped-by: David Barr <> Signed-off-by: Jonathan Nieder <>
Diffstat (limited to 'vcs-svn/sliding_window.h')
1 files changed, 17 insertions, 0 deletions
diff --git a/vcs-svn/sliding_window.h b/vcs-svn/sliding_window.h
new file mode 100644
index 0000000..ed0bfdd
--- /dev/null
+++ b/vcs-svn/sliding_window.h
@@ -0,0 +1,17 @@
+#include "strbuf.h"
+struct sliding_view {
+ struct line_buffer *file;
+ off_t off;
+ size_t width;
+ struct strbuf buf;
+#define SLIDING_VIEW_INIT(input) { (input), 0, 0, STRBUF_INIT }
+extern int move_window(struct sliding_view *view, off_t off, size_t width);