gui-win32: fix encoding and decoding of clipboard strings

On Windows, the clipboard strings are encoded in UTF-16.
However, Drawterm considers them as Rune. It used to work
when a Rune was a short, but a Rune is now a int.
The solution is to implement Rune16 functions to
handle UTF-16 strings.

The Rune16 functions were written by Charles Forsyth
as part of Inferno. Balaji Srinivasa integrated them
into Drawterm.

gui-win32/r16.c

@@ -0,0 +1,168 @@
+#define _WIN32_WINNT 0x0500
+#include <windows.h>
+
+#include <u.h>
+#include <libc.h>
+#include "r16.h"
+
+#define Bit(i) (7-(i))
+/* N 0's preceded by i 1's, T(Bit(2)) is 1100 0000 */
+#define T(i) (((1 << (Bit(i)+1))-1) ^ 0xFF)
+/* 0000 0000 0000 0111 1111 1111 */
+#define	RuneX(i) ((1 << (Bit(i) + ((i)-1)*Bitx))-1)
+
+enum
+{
+	Bitx	= Bit(1),
+
+	Tx	= T(1),			/* 1000 0000 */
+	Rune1 = (1<<(Bit(0)+0*Bitx))-1,	/* 0000 0000 0000 0000 0111 1111 */
+
+	Maskx	= (1<<Bitx)-1,		/* 0011 1111 */
+	Testx	= Maskx ^ 0xFF,		/* 1100 0000 */
+
+	SurrogateMin	= 0xD800,
+	SurrogateMax	= 0xDFFF,
+
+	Bad	= Runeerror,
+};
+
+Rune16*
+runes16dup(Rune16 *r)
+{
+	int n;
+	Rune16 *s;
+
+	n = runes16len(r) + 1;
+	s = malloc(n * sizeof(Rune16));
+	memmove(s, r, n * sizeof(Rune16));
+	return s;
+}
+
+int
+runes16len(Rune16 *r)
+{
+	int n;
+
+	n = 0;
+	while(*r++ != 0)
+		n++;
+	return n;
+}
+
+char*
+runes16toutf(char *p, Rune16 *r, int nc)
+{
+	char *op, *ep;
+	int n, c;
+	Rune rc;
+
+	op = p;
+	ep = p + nc;
+	while(c = *r++) {
+		n = 1;
+		if(c >= Runeself)
+			n = runelen(c);
+		if(p + n >= ep)
+			break;
+		rc = c;
+		if(c < Runeself)
+			*p++ = c;
+		else
+			p += runetochar(p, &rc);
+	}
+	*p = '\0';
+	return op;
+}
+
+int
+rune16nlen(Rune16 *r, int nrune)
+{
+	int nb, i;
+	Rune c;
+
+	nb = 0;
+	while(nrune--) {
+		c = *r++;
+		if(c <= Rune1){
+			nb++;
+		} else {
+			for(i = 2; i < UTFmax + 1; i++)
+				if(c <= RuneX(i) || i == UTFmax){
+					nb += i;
+					break;
+				}
+		}
+	}
+	return nb;
+}
+
+Rune16*
+utftorunes16(Rune16 *r, char *p, int nc)
+{
+	Rune16 *or, *er;
+	Rune rc;
+
+	or = r;
+	er = r + nc;
+	while(*p != '\0' && r + 1 < er){
+		p += chartorune(&rc, p);
+		*r++ = rc;	/* we'll ignore surrogate pairs */
+	}
+	*r = '\0';
+	return or;
+}
+
+int
+runes16cmp(Rune16 *s1, Rune16 *s2)
+{
+	Rune16 r1, r2;
+
+	for(;;) {
+		r1 = *s1++;
+		r2 = *s2++;
+		if(r1 != r2) {
+			if(r1 > r2)
+				return 1;
+			return -1;
+		}
+		if(r1 == 0)
+			return 0;
+	}
+}
+
+wchar_t *
+widen(char *s)
+{
+	int n;
+	wchar_t *ws;
+
+	n = utflen(s) + 1;
+	ws = smalloc(n*sizeof(wchar_t));
+	utftorunes16(ws, s, n);
+	return ws;
+}
+
+
+char *
+narrowen(wchar_t *ws)
+{
+	char *s;
+	int n;
+
+	n = widebytes(ws);
+	s = smalloc(n);
+	runes16toutf(s, ws, n);
+	return s;
+}
+
+
+int
+widebytes(wchar_t *ws)
+{
+	int n = 0;
+
+	while (*ws)
+		n += runelen(*ws++);
+	return n+1;
+}