From: Crystal Kolipe <kolipe.c@exoticsilicon.com>
Subject: Re: rasops32: fix fonts on byte swapped framebuffers
To: Ted Bullock <tbullock@comlore.com>, tech@openbsd.org
Date: Thu, 08 Oct 2026 12:19:02 -0000

On Thu, Oct 08, 2026 at 11:33:57AM -0000, Crystal Kolipe wrote:
> The attached patch replaces the union-based type punning with bit-shifting.

Here is a cleaner version.  The elaborate array initialisation using:

> ((uint64_t)((uint64_t)b * 0x100000001)) ^ (((i & 1)) * R_DH)
>     ^ (((i & 2) >> 1) * R_DL)

... in the previous version was left over from trying to do the calculation on
the fly for each pixel pair, (which was significantly slower).


--- rasops32.c
+++ rasops32.c
@@ -68,10 +68,7 @@
 	uint32_t fb, clr[2];
 	struct rasops_info *ri;
 	int64_t *rp;
-	union {
-		int64_t q[4];
-		int32_t d[4][2];
-	} u;
+	uint64_t u_dot_q[4];
 	u_char *fr;
 
 	ri = (struct rasops_info *)cookie;
@@ -93,11 +90,12 @@
 
 	b = ri->ri_devcmap[(attr >> 16) & 0xf];
 	f = ri->ri_devcmap[(attr >> 24) & 0xf];
-	u.d[0][0] = b; u.d[0][1] = b;
-	u.d[1][0] = b; u.d[1][1] = f;
-	u.d[2][0] = f; u.d[2][1] = b;
-	u.d[3][0] = f; u.d[3][1] = f;
 
+	u_dot_q[0] = (uint64_t)b | (uint64_t)b << 32;
+	u_dot_q[1] = (uint64_t)b | (uint64_t)f << 32;
+	u_dot_q[2] = (uint64_t)f | (uint64_t)b << 32;
+	u_dot_q[3] = (uint64_t)f | (uint64_t)f << 32;
+
 	if (uc == ' ') {
 		while (height--) {
 			/* the general, pixel-at-a-time case is fast enough */
@@ -115,9 +113,9 @@
 		case 6:
 			while (height--) {
 				fb = fr[0];
-				rp[0] = u.q[fb >> 6];
-				rp[1] = u.q[(fb >> 4) & 3];
-				rp[2] = u.q[(fb >> 2) & 3];
+				rp[0] = u_dot_q[fb >> 6];
+				rp[1] = u_dot_q[(fb >> 4) & 3];
+				rp[2] = u_dot_q[(fb >> 2) & 3];
 				rp += step;
 				fr += 1;
 			}
@@ -126,10 +124,10 @@
 		case 8:
 			while (height--) {
 				fb = fr[0];
-				rp[0] = u.q[fb >> 6];
-				rp[1] = u.q[(fb >> 4) & 3];
-				rp[2] = u.q[(fb >> 2) & 3];
-				rp[3] = u.q[fb & 3];
+				rp[0] = u_dot_q[fb >> 6];
+				rp[1] = u_dot_q[(fb >> 4) & 3];
+				rp[2] = u_dot_q[(fb >> 2) & 3];
+				rp[3] = u_dot_q[fb & 3];
 				rp += step;
 				fr += 1;
 			}
@@ -138,13 +136,13 @@
 		case 12:
 			while (height--) {
 				fb = fr[0];
-				rp[0] = u.q[fb >> 6];
-				rp[1] = u.q[(fb >> 4) & 3];
-				rp[2] = u.q[(fb >> 2) & 3];
-				rp[3] = u.q[fb & 3];
+				rp[0] = u_dot_q[fb >> 6];
+				rp[1] = u_dot_q[(fb >> 4) & 3];
+				rp[2] = u_dot_q[(fb >> 2) & 3];
+				rp[3] = u_dot_q[fb & 3];
 				fb = fr[1];
-				rp[4] = u.q[fb >> 6];
-				rp[5] = u.q[(fb >> 4) & 3];
+				rp[4] = u_dot_q[fb >> 6];
+				rp[5] = u_dot_q[(fb >> 4) & 3];
 				rp += step;
 				fr += 2;
 			}
@@ -153,15 +151,15 @@
 		case 16:
 			while (height--) {
 				fb = fr[0];
-				rp[0] = u.q[fb >> 6];
-				rp[1] = u.q[(fb >> 4) & 3];
-				rp[2] = u.q[(fb >> 2) & 3];
-				rp[3] = u.q[fb & 3];
+				rp[0] = u_dot_q[fb >> 6];
+				rp[1] = u_dot_q[(fb >> 4) & 3];
+				rp[2] = u_dot_q[(fb >> 2) & 3];
+				rp[3] = u_dot_q[fb & 3];
 				fb = fr[1];
-				rp[4] = u.q[fb >> 6];
-				rp[5] = u.q[(fb >> 4) & 3];
-				rp[6] = u.q[(fb >> 2) & 3];
-				rp[7] = u.q[fb & 3];
+				rp[4] = u_dot_q[fb >> 6];
+				rp[5] = u_dot_q[(fb >> 4) & 3];
+				rp[6] = u_dot_q[(fb >> 2) & 3];
+				rp[7] = u_dot_q[fb & 3];
 				rp += step;
 				fr += 2;
 			}
@@ -170,25 +168,25 @@
 		case 32:
 			while (height--) {
 				fb = fr[0];
-				rp[0] = u.q[fb >> 6];
-				rp[1] = u.q[(fb >> 4) & 3];
-				rp[2] = u.q[(fb >> 2) & 3];
-				rp[3] = u.q[fb & 3];
+				rp[0] = u_dot_q[fb >> 6];
+				rp[1] = u_dot_q[(fb >> 4) & 3];
+				rp[2] = u_dot_q[(fb >> 2) & 3];
+				rp[3] = u_dot_q[fb & 3];
 				fb = fr[1];
-				rp[4] = u.q[fb >> 6];
-				rp[5] = u.q[(fb >> 4) & 3];
-				rp[6] = u.q[(fb >> 2) & 3];
-				rp[7] = u.q[fb & 3];
+				rp[4] = u_dot_q[fb >> 6];
+				rp[5] = u_dot_q[(fb >> 4) & 3];
+				rp[6] = u_dot_q[(fb >> 2) & 3];
+				rp[7] = u_dot_q[fb & 3];
 				fb = fr[2];
-				rp[8] = u.q[fb >> 6];
-				rp[9] = u.q[(fb >> 4) & 3];
-				rp[10] = u.q[(fb >> 2) & 3];
-				rp[11] = u.q[fb & 3];
+				rp[8] = u_dot_q[fb >> 6];
+				rp[9] = u_dot_q[(fb >> 4) & 3];
+				rp[10] = u_dot_q[(fb >> 2) & 3];
+				rp[11] = u_dot_q[fb & 3];
 				fb = fr[3];
-				rp[12] = u.q[fb >> 6];
-				rp[13] = u.q[(fb >> 4) & 3];
-				rp[14] = u.q[(fb >> 2) & 3];
-				rp[15] = u.q[fb & 3];
+				rp[12] = u_dot_q[fb >> 6];
+				rp[13] = u_dot_q[(fb >> 4) & 3];
+				rp[14] = u_dot_q[(fb >> 2) & 3];
+				rp[15] = u_dot_q[fb & 3];
 				rp += step;
 				fr += 4;
 			}