softwrap: count softwrapped chunks properly in do_uncut_text()

Add the new function less_than_a_screenful() to accomplish this.
It uses go_back_chunks() to count the number of softwrapped chunks
between the end point and the starting point of the paste.

Now softwrap mode and non-softwrap mode behave the same way when
uncutting fewer than editwinrows rows of text.  Accordingly, remove
the call to ensure_line_is_visible(), as it no longer applies.

src/cut.c

@@ -257,6 +257,9 @@ void do_cut_till_eof(void)
 void do_uncut_text(void)
 {
     ssize_t was_lineno = openfile->current->lineno;
+	/* The line number where we started the paste. */
+    size_t was_leftedge = 0;
+	/* The leftedge where we started the paste. */
 
     /* If the cutbuffer is empty, there is nothing to do. */
     if (cutbuffer == NULL)
@@ -264,6 +267,9 @@ void do_uncut_text(void)
 
 #ifndef NANO_TINY
     add_undo(PASTE);
+
+    if (ISSET(SOFTWRAP))
+	was_leftedge = (xplustabs() / editwincols) * editwincols;
 #endif
 
     /* Add a copy of the text in the cutbuffer to the current filestruct
@@ -274,7 +280,8 @@ void do_uncut_text(void)
     update_undo(PASTE);
 #endif
 
-    if (openfile->current->lineno - was_lineno < editwinrows)
+    /* If we pasted less than a screenful, don't center the cursor. */
+    if (less_than_a_screenful(was_lineno, was_leftedge))
 	focusing = FALSE;
 
     /* Set the desired x position to where the pasted text ends. */
@@ -286,8 +293,6 @@ void do_uncut_text(void)
     /* Update the cursor position to account for the inserted lines. */
     reset_cursor();
 
-    ensure_line_is_visible();
-
     refresh_needed = TRUE;
 
 #ifndef DISABLE_COLOR

src/proto.h

@@ -709,6 +709,7 @@ int update_line(filestruct *fileptr, size_t index);
 bool need_horizontal_scroll(const size_t old_column, const size_t new_column);
 int go_back_chunks(int nrows, filestruct **line, size_t *leftedge);
 int go_forward_chunks(int nrows, filestruct **line, size_t *leftedge);
+bool less_than_a_screenful(size_t was_lineno, size_t was_leftedge);
 void edit_scroll(scroll_dir direction, int nrows);
 void edit_redraw(filestruct *old_current);
 void edit_refresh(void);

src/winio.c

@@ -2835,6 +2835,24 @@ int go_forward_chunks(int nrows, filestruct **line, size_t *leftedge)
     return i;
 }
 
+/* Return TRUE if there are fewer than a screen's worth of lines between
+ * the line at line number was_lineno (and column was_leftedge, if we're
+ * in softwrap mode) and the line at current[current_x]. */
+bool less_than_a_screenful(size_t was_lineno, size_t was_leftedge)
+{
+#ifndef NANO_TINY
+    if (ISSET(SOFTWRAP)) {
+	filestruct *line = openfile->current;
+	size_t leftedge = (xplustabs() / editwincols) * editwincols;
+	int rows_left = go_back_chunks(editwinrows - 1, &line, &leftedge);
+
+	return (rows_left > 0 || line->lineno < was_lineno ||
+		(line->lineno == was_lineno && leftedge <= was_leftedge));
+    } else
+#endif
+	return (openfile->current->lineno - was_lineno < editwinrows);
+}
+
 /* Scroll the edit window in the given direction and the given number of rows,
  * and draw new lines on the blank lines left after the scrolling.  We change
  * edittop, and assume that current and current_x are up to date. */