1 files changed, 79 insertions, 0 deletions
diff --git a/vcs-svn/sliding_window.c b/vcs-svn/sliding_window.c
new file mode 100644
index 0000000000..f11d490995
--- /dev/null
+++ b/vcs-svn/sliding_window.c
@@ -0,0 +1,79 @@
+/*
+ * Licensed under a two-clause BSD-style license.
+ * See LICENSE for details.
+ */
+
+#include "git-compat-util.h"
+#include "sliding_window.h"
+#include "line_buffer.h"
+#include "strbuf.h"
+
+static int input_error(struct line_buffer *file)
+{
+	if (!buffer_ferror(file))
+		return error("delta preimage ends early");
+	return error("cannot read delta preimage: %s", strerror(errno));
+}
+
+static int skip_or_whine(struct line_buffer *file, off_t gap)
+{
+	if (buffer_skip_bytes(file, gap) != gap)
+		return input_error(file);
+	return 0;
+}
+
+static int read_to_fill_or_whine(struct line_buffer *file,
+				struct strbuf *buf, size_t width)
+{
+	buffer_read_binary(file, buf, width - buf->len);
+	if (buf->len != width)
+		return input_error(file);
+	return 0;
+}
+
+static int check_offset_overflow(off_t offset, uintmax_t len)
+{
+	if (len > maximum_signed_value_of_type(off_t))
+		return error("unrepresentable length in delta: "
+				"%"PRIuMAX" > OFF_MAX", len);
+	if (signed_add_overflows(offset, (off_t) len))
+		return error("unrepresentable offset in delta: "
+				"%"PRIuMAX" + %"PRIuMAX" > OFF_MAX",
+				(uintmax_t) offset, len);
+	return 0;
+}
+
+int move_window(struct sliding_view *view, off_t off, size_t width)
+{
+	off_t file_offset;
+	assert(view);
+	assert(view->width <= view->buf.len);
+	assert(!check_offset_overflow(view->off, view->buf.len));
+
+	if (check_offset_overflow(off, width))
+		return -1;
+	if (off < view->off || off + width < view->off + view->width)
+		return error("invalid delta: window slides left");
+	if (view->max_off >= 0 && view->max_off < off + (off_t) width)
+		return error("delta preimage ends early");
+
+	file_offset = view->off + view->buf.len;
+	if (off < file_offset) {
+		/* Move the overlapping region into place. */
+		strbuf_remove(&view->buf, 0, off - view->off);
+	} else {
+		/* Seek ahead to skip the gap. */
+		if (skip_or_whine(view->file, off - file_offset))
+			return -1;
+		strbuf_setlen(&view->buf, 0);
+	}
+
+	if (view->buf.len > width)
+		; /* Already read. */
+	else if (read_to_fill_or_whine(view->file, &view->buf, width))
+		return -1;
+
+	view->off = off;
+	view->width = width;
+	return 0;
+}