| |
|
| : head? ( addr -- f ) |
: head? ( addr -- f ) |
| \G heuristic check whether addr is a name token; may deliver false |
\G heuristic check whether addr is a name token; may deliver false |
| \G positives; addr must be a valid address |
\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 |
\ we follow the link fields and check for plausibility; two |
| \ iterations should catch most false addresses: on the first |
\ iterations should catch most false addresses: on the first |
| \ iteration, we may get an xt, on the second a code address (or |
\ iteration, we may get an xt, on the second a code address (or |
| \ some code), which is typically not in the dictionary. |
\ some code), which is typically not in the dictionary. |
| \ !! does not work se well for simple-see: trips on the first "0" |
|
| 2 0 do |
2 0 do |
| dup dup aligned <> if \ protect @ against unaligned accesses |
dup dup aligned <> if \ protect @ against unaligned accesses |
| drop false unloop exit |
drop false unloop exit |
| drop false unloop exit |
drop false unloop exit |
| then ( addr1 ) |
then ( addr1 ) |
| else \ 0 in the link field, no further checks |
else \ 0 in the link field, no further checks |
| 2drop true unloop exit |
2drop 1 unloop exit \ this is very unsure, so return 1 |
| then |
then |
| loop |
loop |
| \ in dubio pro: |
\ in dubio pro: |
