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rio: do backspace \b processing inplace avoiding buffer allocation

--- a/sys/src/cmd/rio/wind.c

+++ b/sys/src/cmd/rio/wind.c

@@ -164,7 +164,7 @@

 void

 winctl(void *arg)

 {

-	Rune *rp, *bp, *tp, *up;

+	Rune *rp, *up;

 	uint qh, q0;

 	int nr, nb, c, wid, i, npart, initial, lastb;

 	char *s, *t, part[3];

@@ -346,23 +346,18 @@

 			recv(cwm.cw, &pair);

 			rp = pair.s;

 			nr = pair.ns;

-			bp = rp;

 			for(i=0; i<nr; i++)

-				if(*bp++ == '\b'){

-					--bp;

+				if(rp[i] == '\b'){

+					up = rp+i;

 					initial = 0;

-					tp = runemalloc(nr);

-					runemove(tp, rp, i);

-					up = tp+i;

 					for(; i<nr; i++){

-						*up = *bp++;

-						if(*up == '\b')

-							if(up == tp)

+						if(rp[i] == '\b'){

+							if(up == rp)

 								initial++;

 							else

-								--up;

-						else

-							up++;

+								up--;

+						}else

+							*up++ = rp[i];

 					}

 					if(initial){

 						if(initial > w->qh)

@@ -371,10 +366,7 @@

 						wdelete(w, qh, qh+initial);

 						w->qh = qh;

 					}

-					free(rp);

-					rp = tp;

-					nr = up-tp;

-					rp[nr] = 0;

+					nr = up - rp;

 					break;

 				}

 			w->qh = winsert(w, rp, nr, w->qh)+nr;

-- 

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