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Author SHA1 Message Date
Virgil Dupras
ed2b91411a Limit ourselves to 8-bit branching
I'm planning on going back to 8-bit branching. 16-bit br cells incur
a non-negligible penalty and, while at first 64 words (128 bytes
forward or backward) seemed a bit limiting, I now don't see why one
would ever construct such a big branch. It would be un-forthy.

Also, I looked at using BC instead of IY to hold IP and the transition
would be a lot easier with 8-bit branching.

In this commit, all I do is add overflow checks in IF. The mechanic
below doesn't change. I'll give myself some time to think it over so
that I avoid yet another back and forth.
2020-05-24 10:16:25 -04:00
Virgil Dupras
5bbc256faf Flush input buffer on QUIT
Prebiously, when encountering an error during a : ; definition from
input buffer, because the input buffer wasn't flushed, we would continue
interpreting and quit the whole program when encountering ;.
2020-05-24 09:23:19 -04:00
8 changed files with 29 additions and 27 deletions

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21 How blocks are organized 22 Addressed devices 21 How blocks are organized 22 Addressed devices
23 Branching

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blk/023 Normal file
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Branching
Branching in Collapse OS is limited to 8-bit. This represents
64 word references forward or backward. While this might seem
a bit tight at first, having this limit saves us a non-
negligible amount of resource usage.
The reasoning behind this intentional limit is that huge
branches are generally a indicator that a logic ought to be
simplified. So here's one more constraint for you to help you
towards simplicity.

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blk/353
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: RAM+ [ RAMSTART LITN ] + ; : RAM+ [ RAMSTART LITN ] + ; : BIN+ [ BIN( @ LITN ] + ;
: BIN+ [ BIN( @ LITN ] + ;
: HERE 0x04 RAM+ ; : HERE 0x04 RAM+ ;
: CURRENT* 0x51 RAM+ ; : CURRENT* 0x51 RAM+ ; : CURRENT CURRENT* @ ;
: CURRENT CURRENT* @ ;
: H@ HERE @ ; : H@ HERE @ ;
: FIND ( w -- a f ) CURRENT @ SWAP _find ; : FIND ( w -- a f ) CURRENT @ SWAP _find ;
: IN> 0x30 RAM+ ; ( current position in INBUF )
: IN( 0x32 RAM+ @ ; ( points to INBUF )
: IN) 0x40 ( buffer size ) IN( + ; ( INBUF's end )
: (infl) 0 IN( DUP IN> ! ! ; ( flush input buffer )
: QUIT : QUIT
(resRS) (resRS) 0 0x08 RAM+ ! ( C<* override ) (infl)
0 0x08 RAM+ ! ( 08 == C<* override )
LIT< (main) FIND DROP EXECUTE LIT< (main) FIND DROP EXECUTE
; ;
1 25 LOADR+ ( xcomp core low ) 1 25 LOADR+ ( xcomp core low )

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blk/386
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( current position in INBUF )
: IN> 0x30 RAM+ ;
( points to INBUF )
: IN( 0x32 RAM+ @ ;
( points to INBUF's end )
: IN) 0x40 ( buffer size ) IN( + ;
( flush input buffer )
( set IN> to IN( and set IN> @ to null )
: (infl) 0 IN( DUP IN> ! ! ;

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( Now we have "as late as possible" stuff ) ( Now we have "as late as possible" stuff )
: _bchk DUP 0x7f + 0xff > IF LIT< br-ovfl (print) ABORT THEN ;
: DO COMPILE 2>R H@ ; IMMEDIATE : DO COMPILE 2>R H@ ; IMMEDIATE
: LOOP COMPILE (loop) H@ - , ; IMMEDIATE : LOOP COMPILE (loop) H@ - _bchk , ; IMMEDIATE
( LEAVE is implemented in low xcomp ) ( LEAVE is implemented in low xcomp )
: LITN 32 , , ( 32 == NUMBER ) ; : LITN 32 , , ( 32 == NUMBER ) ;
( gets its name at the very end. can't comment afterwards ) ( gets its name at the very end. can't comment afterwards )

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COMPILE (?br) H@ 2 ALLOT ( br cell allot ) COMPILE (?br) H@ 2 ALLOT ( br cell allot )
; IMMEDIATE ; IMMEDIATE
: THEN ( a -- | a: br cell addr ) : THEN ( a -- | a: br cell addr )
DUP H@ -^ SWAP ( a-H a ) ! DUP H@ -^ _bchk SWAP ( a-H a ) !
; IMMEDIATE ; IMMEDIATE
: ELSE ( a1 -- a2 | a1: IF cell a2: ELSE cell ) : ELSE ( a1 -- a2 | a1: IF cell a2: ELSE cell )
COMPILE (br) COMPILE (br)
2 ALLOT 2 ALLOT
DUP H@ -^ SWAP ( a-H a ) [COMPILE] THEN
!
H@ 2- ( push a. -2 for allot offset ) H@ 2- ( push a. -2 for allot offset )
; IMMEDIATE ; IMMEDIATE

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: BEGIN H@ ; IMMEDIATE : BEGIN H@ ; IMMEDIATE
: AGAIN COMPILE (br) H@ - , ; IMMEDIATE : AGAIN COMPILE (br) H@ - _bchk , ; IMMEDIATE
: UNTIL COMPILE (?br) H@ - , ; IMMEDIATE : UNTIL COMPILE (?br) H@ - _bchk , ; IMMEDIATE
: [ INTERPRET ; IMMEDIATE : [ INTERPRET ; IMMEDIATE
: ] R> DROP ; : ] R> DROP ;
: LIT< WORD 34 , SCPY 0 C, ; IMMEDIATE : LIT< WORD 34 , SCPY 0 C, ; IMMEDIATE

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