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World: r3wp

[rebcode] Rebcode discussion

BrianH
23-Feb-2007
[1909]
You could even generate more of your interpreter by using more interesting 
macros, which would cut down on the programmer overhead of the increased 
number of states in your state machine.
Steeve
23-Feb-2007
[1910x4]
like what ?
like iterative macros
currently i want keep ly source readable
but after the debuguing phase, i think i could compact the code with 
more macros, i agree
BrianH
23-Feb-2007
[1914]
Perhaps you could specify your operations in a table and then go 
through it with a dialect processor like BURG - REBOL is good at 
that sort of thing. Then you could generate your interpreter from 
that table.
Steeve
23-Feb-2007
[1915]
BURG ? sort of beer effect ?
BrianH
23-Feb-2007
[1916]
No, BURG is a tool used to generate backends for compilers from a 
processor specification dialect.
Steeve
23-Feb-2007
[1917]
:-)
BrianH
23-Feb-2007
[1918x2]
It's for compilers written in C. I think you could do something like 
BURG in a few lines of REBOL though :)
Plus the input data, of course.
Steeve
23-Feb-2007
[1920x3]
or you could add a a ReBurg function in the Rebol VM , to do that 
in my place :-)
don't knwo Burg dialect
*know
BrianH
23-Feb-2007
[1923x2]
The dialect you would use probably wouldn't look much like BURG, 
since you are generating an interpreter.
Your generator would probably act a lot more like a peephole optimizer.
Steeve
23-Feb-2007
[1925]
BTW, why rebcode thread is not on rebol.net ?
BrianH
23-Feb-2007
[1926]
Few of the groups are. If I had to guess, it would be to avoid the 
reputation of vaporware. It has been a while since they have done 
a version of REBOL with rebcode, and it had some significant shortcomings. 
There may be no reason, though.
Steeve
23-Feb-2007
[1927x3]
BrianH i test some changed with rebcode on my video emulation of 
the MSX, it seems than some native rebol instructions are more faster 
with image handling than rebcode
for example i can copy one image to another one with change instruction 
but  not using rebcode
rebcode can only handle byte series
BrianH
23-Feb-2007
[1930x2]
Yeah, rebcode just cuts down on interpreter overhead, but since its 
operations are a bit lower-level they aren't necessarily as fast. 
For simple operations it can be much faster, but natives are just 
that, optimized native code.
Fortunately you can call the natives with the apply opcode and get 
the best of both worlds.
Steeve
23-Feb-2007
[1932x3]
fortunatly :)
my interpreter  will be faster if any math operations could act on 
char (one byte)
and if more flags was handled
BrianH
23-Feb-2007
[1935]
That isn't always the case with modern processors - some work faster 
with integers. I agree on the flags though, in your case.
Steeve
23-Feb-2007
[1936x5]
could the T flag be set after a locial operation like AND ?
very usefull to test if a bit is set
*after a logical operation
for example, if i want to test the 7th bit , i do
and  var 128
ift [ do the job]
instead of doing
and var 128
eq.i var 128
ift [ do the job]
BrianH
23-Feb-2007
[1941]
Whae does SETT do here?
Steeve
23-Feb-2007
[1942x2]
sett ?
you mean
BrianH
23-Feb-2007
[1944]
It sets the T flag based on the contents of a variable. I think it 
sets T to false if the var has 0, none or false, and sets T to true 
otherwise.
Steeve
23-Feb-2007
[1945]
and var 128
sett var
ift [do the job]
BrianH
23-Feb-2007
[1946x2]
Yeah.
Try it. My memory of the behavior of SETT on 0 is a little sparse.
Steeve
23-Feb-2007
[1948]
i don't see any gain
BrianH
23-Feb-2007
[1949]
It would be faster than a compare.
Steeve
23-Feb-2007
[1950x4]
i use 3 instructions to test a bit in all cases
should have:
bit 7 [do the job]
:-)
missing the operand
BrianH
23-Feb-2007
[1954]
I'm curious, did you check SETT to see if the value 0 sets the T 
flag to false?
Steeve
23-Feb-2007
[1955x3]
no sorry , i test now
it works
anyway it's not really a problem, i never perform such tests
BrianH
23-Feb-2007
[1958]
Cool. So SETT can replace ZERO? and NONE?, which otherwise don't 
have rebcode equivalents.