vcs-svn: rename check_overflow and its arguments for clarity

The canonical interpretation of a range a,b is as an interval [a,b),
not [a,a+b), so this function taking argument names a and b feels
unnatural.  Use more explicit names "offset" and "len" to make the
arguments' type and function clearer.

While at it, rename the function to convey that we are making sure
the sum of this offset and length do not overflow an off_t, not a
size_t.

[jn: split out from a patch from Ramsay Jones, then improved with
 advice from Thomas Rast, Dmitry Ivankov, and David Barr]

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Improved-by: Dmitry Ivankov <divanorama@gmail.com>

vcs-svn/sliding_window.c

@@ -31,15 +31,15 @@ static int read_to_fill_or_whine(struct line_buffer *file,
 	return 0;
 }
 
-static int check_overflow(off_t a, size_t b)
+static int check_offset_overflow(off_t offset, size_t len)
 {
-	if (b > maximum_signed_value_of_type(off_t))
+	if (len > maximum_signed_value_of_type(off_t))
 		return error("unrepresentable length in delta: "
-				"%"PRIuMAX" > OFF_MAX", (uintmax_t) b);
-	if (signed_add_overflows(a, (off_t) b))
+				"%"PRIuMAX" > OFF_MAX", (uintmax_t) len);
+	if (signed_add_overflows(offset, (off_t) len))
 		return error("unrepresentable offset in delta: "
 				"%"PRIuMAX" + %"PRIuMAX" > OFF_MAX",
-				(uintmax_t) a, (uintmax_t) b);
+				(uintmax_t) offset, (uintmax_t) len);
 	return 0;
 }
 
@@ -48,9 +48,9 @@ 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_overflow(view->off, view->buf.len));
+	assert(!check_offset_overflow(view->off, view->buf.len));
 
-	if (check_overflow(off, width))
+	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");