Weird calculation for kernel L2 segment table

sys/arch/amiga/amiga/amiga_init.c (and recently sync'ed atari_init.c)
has the following calculations to get the level2 segment table
for the kernel Sysptmap:

---
		/*
		 * Kernel segment table at end of next level 2 table
		 */
		/* XXX fix calculations XXX */
		i = ((((ptsize >> PGSHIFT) + 3) & -2) - 1) * (NPTEPG / SG4_LEV3SIZE);
		sg = &((st_entry_t *)(RELOC(Sysseg_pa, u_int)))[SG4_LEV1SIZE + i];
		esg = &sg[NPTEPG / SG4_LEV3SIZE];
		sg_proto = Sysptmap_pa | SG_U | SG_RW | SG_V;
		while (sg < esg) {
			*sg++ = sg_proto;
			sg_proto += (SG4_LEV3SIZE * sizeof (st_entry_t));
		}
---

I think this could be rewritten more meaningfully as following:

---
		nl2desc = (ptsize >> PGSHIFT) * (NPTEPG / SG4_LEV3SIZE);
	:
		nl1desc = roundup(nl2desc, SG4_LEV2SIZE) / SG4_LEV2SIZE;
	:
		/*
		 * Kernel segment table at end of next level 2 table
		 */
		i = SG4_LEV1SIZE + (nl1desc * SG4_LEV2SIZE);
		sg = (st_entry_t *)RELOC(Sysseg_pa, u_int);
		sg = &sg[i + SG4_LEV2SIZE - (NPTEPG / SG4_LEV3SIZE)];
		esg = &sg[NPTEPG / SG4_LEV3SIZE];
	:
---

With a quick test program, both offset values against Sysseg_pa
look identical.

How about this patch? Comments?

---
Index: amiga/amiga/amiga_init.c
===================================================================
RCS file: /cvsroot/src/sys/arch/amiga/amiga/amiga_init.c,v
retrieving revision 1.103
diff -u -r1.103 amiga_init.c
--- amiga/amiga/amiga_init.c	31 Dec 2008 19:54:40 -0000	1.103
+++ amiga/amiga/amiga_init.c	2 Jan 2009 04:44:43 -0000
@@ -218,6 +218,9 @@
 	register pt_entry_t pg_proto, *pg, *epg;
 	vaddr_t end_loaded;
 	u_int ncd, i;
+#if defined(M68040) || defined(M68060)
+	u_int nl1desc, nl2desc;
+#endif
 	vaddr_t kva;
 	struct boot_memlist *ml;
 
@@ -432,9 +435,10 @@
 		 * pages of PTEs.  Note that we set the "used" bit
 		 * now to save the HW the expense of doing it.
 		 */
-		i = (ptsize >> PGSHIFT) * (NPTEPG / SG4_LEV3SIZE);
-		sg = &((st_entry_t *)(RELOC(Sysseg_pa, u_int)))[SG4_LEV1SIZE];
-		esg = &sg[i];
+		nl2desc = (ptsize >> PGSHIFT) * (NPTEPG / SG4_LEV3SIZE);
+		sg = (st_entry_t *)RELOC(Sysseg_pa, u_int);
+		sg = &sg[SG4_LEV1SIZE];
+		esg = &sg[nl2desc];
 		sg_proto = ptpa | SG_U | SG_RW | SG_V;
 		while (sg < esg) {
 			*sg++ = sg_proto;
@@ -443,15 +447,13 @@
 
 		/*
 		 * Initialize level 1 descriptors.  We need:
-		 *	roundup(num, SG4_LEV2SIZE) / SG4_LEVEL2SIZE
-		 * level 1 descriptors to map the 'num' level 2's.
+		 *	roundup(nl2desc, SG4_LEV2SIZE) / SG4_LEVEL2SIZE
+		 * level 1 descriptors to map the 'nl2desc' level 2's.
 		 */
-		i = roundup(i, SG4_LEV2SIZE) / SG4_LEV2SIZE;
+		nl1desc = roundup(nl2desc, SG4_LEV2SIZE) / SG4_LEV2SIZE;
 		/* Include additional level 2 table for Sysmap in protostfree */
-		RELOC(protostfree, u_int) =
-		    (-1 << (i + 2)) /* & ~(-1 << MAXKL2SIZE) */;
 		sg = (st_entry_t *)RELOC(Sysseg_pa, u_int);
-		esg = &sg[i];
+		esg = &sg[nl1desc];
 		sg_proto = (paddr_t)&sg[SG4_LEV1SIZE] | SG_U | SG_RW | SG_V;
 		while (sg < esg) {
 			*sg++ = sg_proto;
@@ -466,15 +468,17 @@
 		/*
 		 * Kernel segment table at end of next level 2 table
 		 */
-		/* XXX fix calculations XXX */
-		i = ((((ptsize >> PGSHIFT) + 3) & -2) - 1) * (NPTEPG / SG4_LEV3SIZE);
-		sg = &((st_entry_t *)(RELOC(Sysseg_pa, u_int)))[SG4_LEV1SIZE + i];
+		i = SG4_LEV1SIZE + (nl1desc * SG4_LEV2SIZE);
+		sg = (st_entry_t *)RELOC(Sysseg_pa, u_int);
+		sg = &sg[i + SG4_LEV2SIZE - (NPTEPG / SG4_LEV3SIZE)];
 		esg = &sg[NPTEPG / SG4_LEV3SIZE];
 		sg_proto = Sysptmap_pa | SG_U | SG_RW | SG_V;
 		while (sg < esg) {
 			*sg++ = sg_proto;
 			sg_proto += (SG4_LEV3SIZE * sizeof (st_entry_t));
 		}
+		RELOC(protostfree, u_int) =
+		    (-1 << (1 + nl1desc + 1)) /* & ~(-1 << MAXKL2SIZE) */;
 
 		/*
 		 * Initialize Sysptmap
Index: atari/atari/atari_init.c
===================================================================
RCS file: /cvsroot/src/sys/arch/atari/atari/atari_init.c,v
retrieving revision 1.70
diff -u -r1.70 atari_init.c
--- atari/atari/atari_init.c	2 Jan 2009 04:38:09 -0000	1.70
+++ atari/atari/atari_init.c	2 Jan 2009 04:44:43 -0000
@@ -981,7 +981,7 @@
 	paddr_t		sysptmap_pa;	/* System page table		*/
 	paddr_t		kbase;
 {
-	int		i;
+	int		nl1desc, nl2desc, i;
 	st_entry_t	sg_proto, *sg, *esg;
 	pt_entry_t	pg_proto, *pg, *epg;
 
@@ -1003,10 +1003,10 @@
 	 * pages of PTEs.  Note that we set the "used" bit
 	 * now to save the HW the expense of doing it.
 	 */
-	i   = (ptsize >> PGSHIFT) * (NPTEPG / SG4_LEV3SIZE);
+	nl2desc = (ptsize >> PGSHIFT) * (NPTEPG / SG4_LEV3SIZE);
 	sg  = (st_entry_t *)sysseg_pa;
 	sg  = &sg[SG4_LEV1SIZE];
-	esg = &sg[i];
+	esg = &sg[nl2desc];
 	sg_proto = (ptpa + kbase) /* relocated PA */ | SG_U | SG_RW | SG_V;
 	while (sg < esg) {
 		*sg++     = sg_proto;
@@ -1015,13 +1015,12 @@
 
 	/*
 	 * Initialize level 1 descriptors.  We need:
-	 *	roundup(num, SG4_LEV2SIZE) / SG4_LEVEL2SIZE
-	 * level 1 descriptors to map the 'num' level 2's.
+	 *	roundup(nl2desc, SG4_LEV2SIZE) / SG4_LEVEL2SIZE
+	 * level 1 descriptors to map the 'nl2desc' level 2's.
 	 */
-	i   = roundup(i, SG4_LEV2SIZE) / SG4_LEV2SIZE;
-	protostfree = (-1 << (i + 2)) /* & ~(-1 << MAXKL2SIZE) */;
+	nl1desc = roundup(nl2desc, SG4_LEV2SIZE) / SG4_LEV2SIZE;
 	sg  = (st_entry_t *)sysseg_pa;
-	esg = &sg[i];
+	esg = &sg[nl1desc];
 	sg_proto = ((paddr_t)&sg[SG4_LEV1SIZE] + kbase) /* relocated PA */
 	    | SG_U | SG_RW | SG_V;
 	while (sg < esg) {
@@ -1037,10 +1036,9 @@
 	/*
 	 * Kernel segment table at end of next level 2 table
 	 */
-	/* XXX fix calculations XXX */
-	i = ((((ptsize >> PGSHIFT) + 3) & -2) - 1) * (NPTEPG / SG4_LEV3SIZE);
+	i = SG4_LEV1SIZE + (nl1desc * SG4_LEV2SIZE);
 	sg  = (st_entry_t *)sysseg_pa;
-	sg  = &sg[SG4_LEV1SIZE + i];
+	sg  = &sg[i + SG4_LEV2SIZE - (NPTEPG / SG4_LEV3SIZE)];
 	esg = &sg[NPTEPG / SG4_LEV3SIZE];
 	sg_proto = (sysptmap_pa + kbase) /* relocated PA */
 	    | SG_U | SG_RW | SG_V;
@@ -1048,6 +1046,7 @@
 		*sg++ = sg_proto;
 		sg_proto += (SG4_LEV3SIZE * sizeof(st_entry_t));
 	}
+	protostfree = (-1 << (1 + nl1desc + 1)) /* & ~(-1 << MAXKL2SIZE) */;
 
 	/*
 	 * Initialize Sysptmap

---
Izumi Tsutsui