mg - scrolling back diff

[Mark Lumsden]

Currently, mg's cursor jumps from top to bottom of the screen as you
scroll upwards, I find this behaviour confusing at times. This diff
makes mg's scroll back the same as emacs. 

Comments/ok?

mark

Index: basic.c
===================================================================
RCS file: /cvs/src/usr.bin/mg/basic.c,v
retrieving revision 1.32
diff -u -p -r1.32 basic.c
--- basic.c     30 May 2012 06:13:32 -0000      1.32
+++ basic.c     31 May 2012 06:57:11 -0000
@@ -301,7 +301,7 @@ forwpage(int f, int n)
 int
 backpage(int f, int n)
 {
-       struct line  *lp;
+       struct line  *lp, *lp2;
 
        if (!(f & FFARG)) {
                n = curwp->w_ntrows - 2;        /* Default scroll.       */
@@ -309,18 +309,24 @@ backpage(int f, int n)
                        n = 1;                  /* window is tiny.       */
        } else if (n < 0)
                return (forwpage(f | FFRAND, -n));
-       lp = curwp->w_linep;
+
+       lp = lp2 = curwp->w_linep;
+
        while (n-- && lback(lp) != curbp->b_headp) {
                lp = lback(lp);
        }
        curwp->w_linep = lp;
        curwp->w_rflag |= WFFULL;
+
        /* if in current window, don't move dot */
        for (n = curwp->w_ntrows; n-- && lp != curbp->b_headp; lp = lforw(lp))
                if (lp == curwp->w_dotp)
                        return (TRUE);
+
+        lp2 = lforw(lp2);
+
        /* Move the dot the slow way, for line nos */
-       while (curwp->w_dotp != curwp->w_linep) {
+       while (curwp->w_dotp != lp2) {
                curwp->w_dotp = lback(curwp->w_dotp);
                curwp->w_dotline--;
        }