Small optimization: instead of branching, we can do UV correction with a single calculation.

main.c

@@ -464,9 +464,9 @@ void drawModel(ps1mdl_t *model, ps1skin_t *skin, int frameCounter)
 		else
 		{
 			// Since we have the texture split into two parts, we need to correct the UVs that are *not* on the seam, instead of the other way round
-			u0 = tc0->onSeam ? tc0->u : tc0->u - halfSkinWidth;
-			u1 = tc1->onSeam ? tc1->u : tc1->u - halfSkinWidth;
-			u2 = tc2->onSeam ? tc2->u : tc2->u - halfSkinWidth;
+			u0 = tc0->u - !tc0->onSeam * halfSkinWidth;
+			u1 = tc1->u - !tc1->onSeam * halfSkinWidth;
+			u2 = tc2->u - !tc2->onSeam * halfSkinWidth;
 			tex = &skin->back;
 		}