ldconst isn't implemented yet but the plan is to load various constants
(eg, 0, 1, 2, pi, e, ...).
Stack adjust is useful for adding an offset to the stack pointer without
having to worry about finding it (and it checks for alignment).
nop is just that :)
Due to how OP_RETURN works, a destination is required for any function
returning data, but the caller may not have allocated any space for the
value. Thus the VM maintains a buffer into which the data can be put and
ignored. It also makes a good place for return values when the engine
calls Ruamoko code as trusting progs code with return sizes seems like a
recipe for disaster, especially if the return location is on the C
stack.
It turned out that address mode B was redundant as C with 0 offset
(immediate) was the same (except for the underlying C code of course,
but adding st->b is very cheap). This allowed B to be used for
entity.field for all transfer operations. Thus instructions 0-3 are now
free as load E became load B, and other than the specifics of format
codes for statement printing, transfers+lea are unified.
This makes the v6p instruction table consistent with the ruamoko
instruction table, and clears up some of the ugliness with the load,
store, and assign instructions (. .= and = are now spelled out). I think
I'd still prefer an enum code (faster) but at least this is more
readable.
And provide a table for such for qfcc and the like. With this, using
pr_double_t (for example) in C will cause the double value to always be
8-byte aligned and thus structures shared between gcc and qfcc will be
consistent (with a little fuss to take care of the warts).
And other related fields so integer is now int (and uinteger is uint). I
really don't know why I went with integer in the first place, but this
will make using macros easier for dealing with types.
They are both gone, and pr_pointer_t is now pr_ptr_t (pointer may be a
little clearer than ptr, but ptr is consistent with things like intptr,
and keeps the type name short).
This required delaying the setting of the return pointer by call until
after the current pointer had been saved, and thus passing the desired
pointer into PR_CallFunction (which does have some advantages for C
functions calling progs functions, but some dangers too (should ensure a
128 byte (32 word) buffer when calling untrusted code (which is any,
really)).
This fixes the issue of the data stack not being restored properly
because the returning function needs to return a value from its local
variables (stored on the stack) and accessing stack data below the stack
pointer is a bad idea (sure, no interrupts yet, but who knows...).
Call's operand c is used to specify where the return value of the
function is to be stored. This gets both the correct function being
called, and the value being returned correctly. Test still fails due to
the stack restoration issue.
It currently fails for two reasons:
- call's mode selection is incorrect (never updated from when there was
only the one call instruction and the mode was encoded in operand c)
- return should automatically restore the stack pointer to the value it
had on entry to the function, thus allowing local values stored on
the stack to be safely returned.
I don't know why they were ever signed (oversight at id and just
propagated?). Anyway, this resulted in "unsigned" spreading a bit, but
all to reasonable places.
This has been a long-held wishlist item, really, and I thought I might
as well take the opportunity to add the instructions. The double
versions of STATE require both the nextthink field and time global to be
double (but they're not resolved properly yet: marked with
"FIXME double time" comments).
Also, the frame number for double time state is integer rather than
float.
In the end, I decided any/all/none should be separate from the other
horizontal ops, if I even do them (can be implemented by first
converting to bool, then using the appropriate horizontal operation (& |
etc).
ANY/ALL/NONE have been temporarily removed until I implement the HOPS
(horizontal operations) sub-instructions, which will all both 32-bit and
64-bit operands and several other operations (eg, horizontal add).
All the fancy addressing modes for the conditional branch instructions
have been permanently removed: I decided the gain was too little for the
cost (24 instructions vs 6). JUMP and CALL retain their addressing
modes, though.
Other instructions have been shuffled around a little to fill most of
the holes in the upper block of 256 instructions: just a single small
7-instruction hole.
Rearrangements in the actual engine are mostly just to keep the code
organized. The only real changes were the various IF statements and
dealing with the resulting changes in their addressing.
When creating the tests for lea, I noticed that B was yet another simple
assign, so I decided it was best to drop it and move E into its place
(freeing up another instruction).
