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rasops32: fix fonts on byte swapped framebuffers
On Wed, Oct 07, 2026 at 09:57:14AM -0600, Ted Bullock wrote:
> On Wed, Oct 7, 2026 at 8:29???AM Crystal Kolipe
> <kolipe.c@exoticsilicon.com> wrote:
> >
> > On Wed, Oct 07, 2026 at 06:34:02AM -0600, tbullock@comlore.com wrote:
> > > This patch fixes font rendering on 32 bit byte swapped framebuffers.
> > > The function uses a union to write two 32 bit pixels together as one
> > > 64 bit value. With sparc64's byte swapped access, that reverses the
> > > positions of the two pixels.
> >
> > Wouldn't it be far simpler and give better performance to just create a
> > pixel-swapped font variation in memory the first time this function is called
> > and use that with the existing blitting code on subsequent calls?
> >
> > I did almost exactly that to implement italics and other font variants in
> > rasops32.c.
>
> Honestly I have.a lot of emotional thoughts when I saw the original
> union implementation in this function.
>
> It feels like someone was being needlessly clever and it is also
> completely unsurprising that there are endian adjacent problems when
> someone starts throwing unions around.
The attached patch replaces the union-based type punning with bit-shifting.
Does this produce correct rendering results on your hardware?
Surprisingly, this ran about 5% faster than the original version on a couple
of test machines here.
--- 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 +90,15 @@
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;
+#define R_DL (((uint64_t)b) ^ ((uint64_t)f))
+#define R_DH ((R_DL) << 32)
+#define UDOTQ(i) ((uint64_t)((uint64_t)b * 0x100000001)) ^ (((i & 1)) * R_DH) ^ (((i & 2) >> 1) * R_DL)
+ u_dot_q[0] = UDOTQ(0);
+ u_dot_q[1] = UDOTQ(1);
+ u_dot_q[2] = UDOTQ(2);
+ u_dot_q[3] = UDOTQ(3);
+
if (uc == ' ') {
while (height--) {
/* the general, pixel-at-a-time case is fast enough */
@@ -115,9 +116,9 @@
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 +127,10 @@
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 +139,13 @@
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 +154,15 @@
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 +171,25 @@
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;
}
rasops32: fix fonts on byte swapped framebuffers