Merge pull request #20 from philbudne/master

kernel comments: betwen and pget

src/sys/s4.s

@@ -63,27 +63,33 @@ laci: 0
 
 "** 01-s1.pdf page 22
 
+	" skip if AC between two values (inclusive)
+	"   jms betwen; low_ptr; high_ptr
+	"    <not between>
+	"  <between>
+	" listing has an alternate written in
+	"  (which would require 'lac ptr' instead of 'ptr' args?)
 betwen: 0
-   lmq cmq
+   lmq cmq			" get ~AC in MQ
-   lac betwen i
+   lac betwen i			" get low_ptr
    dac 9f+t
-   isz betwen
+   isz betwen			" skip low_ptr
-   lacq
+   lacq				" get ~AC (-AC-1) from MQ
-   tad 9f+t i
+   tad 9f+t i			" get low-AC-1
-   sma
+   sma				" negative (AC >= low)?
-   jmp 1f
+   jmp 1f			"  no, return w/o skip
-   lac betwen i
+   lac betwen i			" fetch high_ptr
    dac 9f+t
-   isz betwen
+   isz betwen			" skip high_ptr
-   lacq
+   lacq				" get -AC-1
-   tad 9f+t i
+   tad 9f+t i			" add to high value (high-AC-1)
-   cma
+   cma				" complement (AC-high)
-   spa sna
+   spa sna			" AC-high <= 0?
 1:
-   isz betwen
+   isz betwen			"  no: give happy return
-   lacq
+   lacq				" restore ~AC
-   cma
+   cma				" restore AC
-   jmp betwen i
+   jmp betwen i			" return w/o skip
 
 copy: 0
    -1

src/sys/s6.s

@@ -185,69 +185,73 @@ dput: 0
 
 t = t+3
 
+	" allocate a block for a file, returns disk block number
+	" AC/ file offset
+	"   jms pget
+	" AC/ disk block number
 pget: 0
-   lrss 6
+   lrss 6				" convert offset to block
-   dac 9f+t
+   dac 9f+t				" save as t0
    lac i.flags
 
 "** 01-s1.pdf page 37
 
    and o200000
-   sza
+   sza					" large file bit set?
-   jmp 2f
+   jmp 2f				"  yes
-   lac 9f+t
+   lac 9f+t				" no: small file
-   jms betwen; d0; d6
+   jms betwen; d0; d6			" block 0..6?
-      jmp 1f
+      jmp 1f				"  no
-   tad idskpp
+   tad idskpp				" make into block number pointer
-   dac 9f+t
+   dac 9f+t				" save in t0
-   lac 9f+t i
+   lac 9f+t i				" get disk block number
-   sna
+   sna					" allocated?
-   jms alloc
+   jms alloc				"  no: allocate now
-   dac 9f+t i
+   dac 9f+t i				" save (new) disk block number
-   jmp pget i
+   jmp pget i				" return disk block number
-1:
+1:					" here when file block>=7, not "large"
-   jms alloc
+   jms alloc				" allocate indirect block
-   dac 9f+t+1
+   dac 9f+t+1				" save as t1
-   jms copy; i.dskps; dskbuf; 7
+   jms copy; i.dskps; dskbuf; 7		" copy all the disk block numbers
-   jms copyz; dskbuf+7; 64-7
+   jms copyz; dskbuf+7; 64-7		" zero rest of indirect block
+   lac 9f+t+1				" get indirect block number back
+   jms dskwr				" write indirect block to disk
    lac 9f+t+1
-   jms dskwr
+   dac i.dskps				" save indirect as new first block
-   lac 9f+t+1
+   jms copyz; i.dskps+1; 6		" zero rest of block pointers
-   dac i.dskps
-   jms copyz; i.dskps+1; 6
    lac i.flags
-   xor o200000
+   xor o200000				" set "large file"
    dac i.flags
-2:
+2:					" here with "large file"
-   lac 9f+t
+   lac 9f+t				" get file block number
-   lrss 6
+   lrss 6				" divide by 64 (indirects/block)
-   jms betwen; d0; d6
+   jms betwen; d0; d6			" ok now?
-      jms halt " file too big
+      jms halt " file too big		"  no, you lose!
-   tad idskpp
+   tad idskpp				" yes: get indirect block pointer
-   dac 9f+t+1
+   dac 9f+t+1				" save in t1
-   lac 9f+t+1 i
+   lac 9f+t+1 i				" get indirect block number
-   sna
+   sna					" allocated?
-   jms alloc
+   jms alloc				"  no, get it now
-   dac 9f+t+1 i
+   dac 9f+t+1 i				" save (new) indirect block
-   dac 9f+t+2
+   dac 9f+t+2				" save as t2
-   jms dskrd
+   jms dskrd				" read indirect block
-   lac 9f+t
+   lac 9f+t				" get original block number
-   and o77
+   and o77				" mod by 64
-   tad dskbufp
+   tad dskbufp				" get pointer to disk block number
-   dac 9f+t+1
+   dac 9f+t+1				" save as t1
-   lac 9f+t+1 i
+   lac 9f+t+1 i				" fetch disk block number
-   sza
+   sza					" allocated?
-   jmp pget i
+   jmp pget i				"  yes: return
-   jms alloc
+   jms alloc				" no: allocate data block
-   dac 9f+t
+   dac 9f+t				" save as t0
+   lac 9f+t+2				" get indirect block number
+   jms dskrd				" read it in
+   lac 9f+t				" get data block number
+   dac 9f+t+1 i				" save data block number
    lac 9f+t+2
-   jms dskrd
+   jms dskwr				" write indirect block back
-   lac 9f+t
+   lac 9f+t				" get data block back
-   dac 9f+t+1 i
+   jmp pget i				" return it
-   lac 9f+t+2
-   jms dskwr
-   lac 9f+t
-   jmp pget i
 t = t+3
 
 iwrite: 0