On at 2022-07-12 15:45 -0400, Steve Nickolas wrote:
I haven't uploaded a copy of the new source anywhere yet - it'll
probably be in the next DOSLITE source batch along with my work on a few
other DOS commands, but I don't want to replace the copy I've already
uploaded, and DOSLITE isn't ready to go onto anything like github or
gitlab yet.
I strongly suggest to keep source history. If you'd rather not, you do
not need to publish that right now but I do recommend you keep it
privately at least. I started in 2010 [1] and it has been a great
experience that often proved useful.
As I said, I managed to move the CP437 table into the spot reserved for
the resident table (except for the first 3 bytes), which saved good
memory, and with C. Masloch's optimizations and by simplifying the
version check the file size and resident footprint went down even
further. (In an earlier incarnation, I had to jigger around 'jmp far
0', but it turns out 'jmp 0:0' as mentioned was the solution to that.)
Yes, good catch, it isn't immediately obvious why NASM won't allow a
"far" keyword there.
The resident footprint went down 1 paragraph, from 1344 to 1328 - now
only 128 bytes larger than the official version. (I wonder if any of
the PSP can be just up and deallocated?)
You can deallocate the PSP (either with some tricks on the parent stack
or just split Memory Control Blocks manually), but it will leave a
memory "hole" in its place. This is seldom useful. (Bret's and my method
relocate the PSP precisely to avoid creating fragmentation holes when
allocating the final resident memory.)
The new "new2F":
new2F: cmp ah, 0xB0 ; is it ours?
je .2
.1: jmp 0:0
.2: cmp al, 1
ja .1 ; >1 - chain
mov al, 0xFF ; needs set for both functions.
je .3 ; 1 - where are we?
iret ; 0 - are we here?
.3: mov word ds:[bx], entry
mov ds:[bx+2], cs
iret
old2F equ .1+1
...probably as codegolfed as it's going to get.
Not quite: The "ds:" segment override prefixes are unneeded actually.
NASM will happily emit them, but they eat memory completely
unnecessarily. "mov word [bx], entry" already defaults to ds as its
segment. (Unlike addresses including "[bp]" which default to ss.)
I didn't notice those at first because I assumed you were using es.
That's what your comment in your caller says:
.21: mov ax, 0xB001 ; So where is it?
mov bx, whence ; ES:BX gets this.
int 0x2F
However, the Interrupt List [2] does say it uses ds:bx so your interrupt
handler is correct, your caller's comment is incorrect.
Regards,
ecm
[1]: https://hg.pushbx.org/ecm/ldebug/rev/5eef5847c863
[2]: https://fd.lod.bz/rbil/interrup/video/2fb001.html#5274
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