/* A sometimes minimal FORTH compiler and tutorial for Linux / i386 systems. -*- asm -*-
By Richard W.M. Jones <rich@annexia.org> http://annexia.org/forth
This is PUBLIC DOMAIN (see public domain release statement below).
- $Id: jonesforth.S,v 1.35 2007-09-26 22:55:50 rich Exp $
+ $Id: jonesforth.S,v 1.36 2007-09-27 23:09:39 rich Exp $
gcc -m32 -nostdlib -static -Wl,-Ttext,0 -o jonesforth jonesforth.S
*/
- .set JONES_VERSION,35
+ .set JONES_VERSION,36
/*
INTRODUCTION ----------------------------------------------------------------------
/*
In this FORTH, only /MOD is primitive. Later we will define the / and MOD words in
- terms of the primitive /MOD.
+ terms of the primitive /MOD. The design of the i386 assembly instruction idiv which
+ leaves both quotient and remainder makes this obvious choice.
*/
defcode "/MOD",4,,DIVMOD
What it does in detail is that it first skips any blanks (spaces, tabs, newlines and so on).
Then it calls KEY to read characters into an internal buffer until it hits a blank. Then it
calculates the length of the word it read and returns the address and the length as
- two words on the stack (with address at the top).
+ two words on the stack (with the length at the top of stack).
Notice that WORD has a single internal buffer which it overwrites each time (rather like
a static C string). Also notice that WORD's internal buffer is just 32 bytes long and
defcode "WORD",4,,WORD
call _WORD
- push %ecx // push length
push %edi // push base address
+ push %ecx // push length
NEXT
_WORD:
*/
defcode "FIND",4,,FIND
- pop %edi // %edi = address
pop %ecx // %ecx = length
+ pop %edi // %edi = address
call _FIND
- push %eax
+ push %eax // %eax = address of dictionary entry (or NULL)
NEXT
_FIND:
defcode "LITSTRING",9,,LITSTRING
lodsl // get the length of the string
- push %eax // push it on the stack
push %esi // push the address of the start of the string
+ push %eax // push it on the stack
addl %eax,%esi // skip past the string
addl $3,%esi // but round up to next 4 byte boundary
andl $~3,%esi
defcode "EMITSTRING",10,,EMITSTRING
mov $1,%ebx // 1st param: stdout
- pop %ecx // 2nd param: address of string
pop %edx // 3rd param: length of string
+ pop %ecx // 2nd param: address of string
mov $__NR_write,%eax // write syscall
int $0x80
NEXT
\ A sometimes minimal FORTH compiler and tutorial for Linux / i386 systems. -*- asm -*-
\ By Richard W.M. Jones <rich@annexia.org> http://annexia.org/forth
\ This is PUBLIC DOMAIN (see public domain release statement below).
-\ $Id: jonesforth.f,v 1.5 2007-09-26 22:20:52 rich Exp $
+\ $Id: jonesforth.f,v 1.6 2007-09-27 23:09:39 rich Exp $
\
\ The first part of this tutorial is in jonesforth.S. Get if from http://annexia.org/forth
\
;
\ A few more character constants defined the same way as above.
+: ';' [ CHAR ; ] LITERAL ;
: '(' [ CHAR ( ] LITERAL ;
: ')' [ CHAR ) ] LITERAL ;
: '"' [ CHAR " ] LITERAL ;
( -- ) means the word has no effect on the stack
)
+( Some more complicated stack examples, showing the stack notation. )
+: NIP ( x y -- y ) SWAP DROP ;
+: TUCK ( x y -- y x y ) DUP ROT ;
+: PICK ( x_u ... x_1 x_0 u -- x_u ... x_1 x_0 x_u )
+ 1+ ( add one because of 'u' on the stack )
+ 4 * ( multiply by the word size )
+ DSP@ + ( add to the stack pointer )
+ @ ( and fetch )
+;
+
( With the looping constructs, we can now write SPACES, which writes n spaces to stdout. )
: SPACES ( n -- )
BEGIN
: U. U. SPACE ;
( ? fetches the integer at an address and prints it. )
-: ? @ . ;
+: ? ( addr -- ) @ . ;
( c a b WITHIN returns true if a <= c and c < b )
: WITHIN
(
S" string" is used in FORTH to define strings. It leaves the address of the string and
- its length on the stack, with the address at the top. The space following S" is the normal
+ its length on the stack, (length at the top of stack). The space following S" is the normal
space between FORTH words and is not a part of the string.
This is tricky to define because it has to do different things depending on whether
case we put the string at HERE (but we _don't_ change HERE). This is meant as a temporary
location, likely to be overwritten soon after.
)
-: S" IMMEDIATE ( -- len addr )
+: S" IMMEDIATE ( -- addr len )
STATE @ IF ( compiling? )
' LITSTRING , ( compile LITSTRING )
HERE @ ( save the address of the length word on the stack )
DROP ( drop the final " character )
HERE @ - ( calculate the length )
HERE @ ( push the start address )
+ SWAP ( addr len )
THEN
;
is the natural size for integers on this machine architecture. On this 32 bit machine therefore
CELLS just multiplies the top of stack by 4.
)
-: CELLS ( n -- n ) 4 * ;
+: CELLS ( n -- n ) 4* ;
(
So now we can define VARIABLE easily in much the same way as CONSTANT above. Refer to the
(
DUMP is used to dump out the contents of memory, in the 'traditional' hexdump format.
+
+ Notice that the parameters to DUMP (address, length) are compatible with string words
+ such as WORD and S".
)
: DUMP ( addr len -- )
BASE @ ROT ( save the current BASE at the bottom of the stack )
BASE ! ( restore saved BASE )
;
+(
+ CFA> is the opposite of >CFA. It takes a codeword and tries to find the matching
+ dictionary definition.
+
+ In this FORTH this is not so easy. In fact we have to search through the dictionary
+ because we don't have a convenient back-pointer (as is often the case in other versions
+ of FORTH).
+
+ This word returns 0 if it doesn't find a match.
+)
+: CFA>
+ LATEST @ ( start at LATEST dictionary entry )
+ BEGIN
+ DUP 0<> ( while link pointer is not null )
+ WHILE
+ DUP >CFA ( cfa curr curr-cfa )
+ 2 PICK ( cfa curr curr-cfa cfa )
+ = IF ( found a match? )
+ NIP ( leave curr dictionary entry on the stack )
+ EXIT ( and return from the function )
+ THEN
+ @ ( follow link pointer back )
+ REPEAT
+ 2DROP ( restore stack )
+ 0 ( sorry, nothing found )
+;
+
+(
+ SEE disassembles a FORTH word.
+
+ We search for the dictionary entry of the word, then search again for the next
+ word (effectively, the end of the compiled word). This results in two pointers:
+
+ +---------+---+---+---+---+------------+------------+------------+------------+
+ | LINK | 3 | T | E | N | DOCOL | LIT | 10 | EXIT |
+ +---------+---+---+---+---+------------+------------+------------+------------+
+ ^ ^
+ | |
+ Start of word End of word
+
+ With this information we can have a go at decompiling the word. We need to
+ recognise "meta-words" like LIT, LITSTRING, BRANCH, etc. and treat those separately.
+)
+: SEE
+ WORD FIND ( find the dictionary entry to decompile )
+
+ ( now we search again, looking for the next word )
+ HERE @ ( address of the end of the last compiled word )
+ LATEST @ ( word last curr )
+ BEGIN
+ 2 PICK ( word last curr word )
+ OVER ( word last curr word curr )
+ <> ( word last curr word<>curr? )
+ WHILE ( word last curr )
+ NIP ( word curr )
+ DUP @ ( word curr prev (which becomes: word last curr) )
+ REPEAT
+
+ DROP ( at this point, the stack is: start-of-word end-of-word )
+ SWAP ( end-of-word start-of-word )
+
+ ( begin the definition with : NAME [IMMEDIATE] )
+ ':' EMIT SPACE DUP ID. SPACE
+ DUP ?IMMEDIATE IF ." IMMEDIATE " THEN
+
+ >DFA ( get the data address, ie. points after DOCOL | end-of-word start-of-data )
+
+ ( now we start decompiling until we hit the end of the word )
+ ( XXX we should ignore the final codeword if it is EXIT )
+ BEGIN ( end start )
+ 2DUP >
+ WHILE
+ DUP @ ( end start codeword )
+
+ DUP ' LIT = IF ( is it LIT ? )
+ DROP
+ 4 + DUP @ ( get next word which is the integer constant )
+ . ( and print it )
+ ELSE
+ DUP ' 0BRANCH = IF ( is it 0BRANCH ? )
+ DROP
+ ." 0BRANCH ( "
+ 4 + DUP @ ( print the offset )
+ .
+ ')' EMIT SPACE
+ ELSE
+ DUP ' BRANCH = IF ( is it BRANCH ? )
+ DROP
+ ." BRANCH ( "
+ 4 + DUP @ ( print the offset )
+ .
+ ')' EMIT SPACE
+ ELSE
+ DUP ' ' = IF ( is it ' (TICK) ? )
+ [ CHAR ' ] LITERAL EMIT SPACE
+ DROP
+ 4 + DUP @ ( get the next codeword )
+ CFA> ( and force it to be printed as a dictionary entry )
+ ID. SPACE
+ ELSE
+ CFA> ( look up the codeword to get the dictionary entry )
+ ID. SPACE ( and print it )
+ THEN
+ THEN
+ THEN
+ THEN
+
+ 4 + ( end start+4 )
+ REPEAT
+
+ ';' EMIT CR
+
+ 2DROP ( restore stack )
+;
+
( Finally print the welcome prompt. )
." JONESFORTH VERSION " VERSION . CR
." OK "
git.annexia.org / jonesforth.git / commitdiff