I have now created a hybrid heuristic test and tested it. It
recognizes fewer names (3158), and the (revised) test against the new
(current) HEAD? shows:
[~/gforth:76432] gforth xxx.fs -e "test cr bye"|grep "hybrid accepts"|wc -l
142
[~/gforth:76433] gforth xxx.fs -e "test cr bye"|grep "new accepts"|wc -l
622
Looking at the output of this test, it appears that there are quite a
number of false negatives coming out of the new HEAD?:
[~/gforth:76434] gforth xxx.fs -e "test cr bye"|grep -B1 recurse
hybrid accepts as head: $7FFFF6BFA7E0 len=7
7FFFF6BFA7F0: 72 65 63 75 72 73 65 - recurse
[~/gforth:76435] gforth xxx.fs -e "test cr bye"|grep -B1 cfalign
hybrid accepts as head: $7FFFF6BF3020 len=9
7FFFF6BF3030: 63 66 61 6C 69 67 6E 65 - 64 cfaligned
--
hybrid accepts as head: $7FFFF6BF9D58 len=7
7FFFF6BF9D68: 63 66 61 6C 69 67 6E - cfalign
Or, more relevantly:
s" recurse" find-name .s <1> 140737333143520 ok
head? . 0 ok
It seems that it does not recognize aliases.
I have tried to put the hybrid version into int.fs and test it, but
the kernel does not work then (this only becomes visible on the next
round of kernel-building). I probably did something wrong wrt cross.fs.
I have now also prepared .VOC to report ??? for unsafe guesses of the
old and hybrid versions. The problem is actually a general problem of
the combination of heuristic HEAD? and .VOC as currently implemented:
A false positive can lead to NAME>INT being called for an
inappropriate address, and NAME>INT will segfault. There's a test of
the CFA at the end of NEW-HEAD?, but is it guaranteed to catch all
cases?
- anton
Here's the code:
\ test head? implementations
: new-head? ( addr -- f )
\G heuristic check whether addr is a name token; may deliver false
\G positives; addr must be a valid address
dup dup aligned <>
if
drop false exit \ heads are aligned
then
name>string dup $20 $1 within if
2drop false exit \ realistically the name is short
then
+ cfaligned @ here forthstart within ; \ and the cfa is outside
: old-head? ( addr -- f )
\G heuristic check whether addr is a name token; may deliver false
\G positives; addr must be a valid address; returns 1 for
\G particularly unsafe positives
\ we follow the link fields and check for plausibility; two
\ iterations should catch most false addresses: on the first
\ iteration, we may get an xt, on the second a code address (or
\ some code), which is typically not in the dictionary.
\ we added a third iteration for working with code and ;code words.
3 0 do
dup dup aligned <> if \ protect @ against unaligned accesses
drop false unloop exit
then
dup @ dup
if ( addr addr1 )
dup rot forthstart within
if \ addr1 is outside forthstart..addr, not a head
drop false unloop exit
then ( addr1 )
else \ 0 in the link field, no further checks
2drop 1 unloop exit \ this is very unsure, so return 1
then
loop
\ in dubio pro:
drop true ;
: hybrid-head? ( addr -- f )
\G heuristic check whether addr is a name token; may deliver false
\G positives; addr must be a valid address; returns 1 for
\G particularly unsafe positives
\ we follow the link fields and check for plausibility; two
\ iterations should catch most false addresses: on the first
\ iteration, we may get an xt, on the second a code address (or
\ some code), which is typically not in the dictionary.
\ we added a third iteration for working with code and ;code words.
3 0 do
dup dup aligned <> if \ protect @ against unaligned accesses
drop false unloop exit
then
dup name>string nip $20 $1 within if
drop false unloop exit \ realistically the name is short
then
dup @ dup if ( addr addr1 )
dup rot forthstart within
if \ addr1 is outside forthstart..addr, not a head
drop false unloop exit
then ( addr1 )
else \ 0 in the link field, no further checks
2drop 1 unloop exit \ this is very unsure, so return 1
then
loop
\ in dubio pro:
drop true ;
: my-.name ( nt -- )
name>string dup ." len=" .
16 min dump ;
: test
here forthstart do
i new-head? 0<> i hybrid-head? 0<> over <> if
cr if
." new"
else
." hybrid"
then
." accepts as head: " i hex. i my-.name
else
drop
then
loop ;
: testhybrid
0 here forthstart do
i hybrid-head? 0<> -
loop ;
