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tables: fix again the handling of useless tokens

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The right-shift added in c22902e360
("tables: fix handling for useless tokens") is incorrect.  In
particular, we need to reset the "new" bits.

Reported by Balázs Scheidler.
https://github.com/akimd/bison/issues/74

* src/tables.c (pos_set_set): Fix the right-shift.
This commit is contained in:
Akim Demaille
2021-03-07 08:19:36 +01:00
parent ef3adfa0fb
commit a774839ca8
2 changed files with 16 additions and 5 deletions
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6
NEWS
View File

@@ -2,6 +2,12 @@ GNU Bison NEWS
* Noteworthy changes in release ?.? (????-??-??) [?] * Noteworthy changes in release ?.? (????-??-??) [?]
** Bug fixes
*** Fix Table Generation
In some very rare conditions, when there are many useless tokens, it was
possible to generate incorrect parsers.
* Noteworthy changes in release 3.7.5 (2021-01-24) [stable] * Noteworthy changes in release 3.7.5 (2021-01-24) [stable]

15
src/tables.c
View File

@@ -180,21 +180,26 @@ pos_set_set (int pos)
int bitno = pos - pos_set_base; int bitno = pos - pos_set_base;
if (bitno < 0) if (bitno < 0)
{ {
// Need more room on the left.
// DELTA is positive. Run 'pos_set >> delta'.
const int delta = pos_set_base - pos; const int delta = pos_set_base - pos;
const int old_size = bitset_size (pos_set); const int old_size = bitset_size (pos_set);
const int new_size = old_size + delta; const int new_size = old_size + delta;
bitset_resize (pos_set, new_size); bitset_resize (pos_set, new_size);
// Shift all the bits by DELTA. // Right-shift all the bits by DELTA. Be sure to reset the new
// bits on the left.
//
// FIXME: add bitset_assign, and bitset_shift? // FIXME: add bitset_assign, and bitset_shift?
for (int i = new_size - 1; delta <= i ; --i) for (int i = new_size - 1; 0 <= i ; --i)
if (bitset_test (pos_set, i)) if (delta <= i && bitset_test (pos_set, i - delta))
bitset_set (pos_set, i + delta); bitset_set (pos_set, i);
else else
bitset_reset (pos_set, i + delta); bitset_reset (pos_set, i);
pos_set_base = pos; pos_set_base = pos;
bitno = 0; bitno = 0;
} }
else if (bitset_size (pos_set) <= bitno) else if (bitset_size (pos_set) <= bitno)
// Need more room on the right.
bitset_resize (pos_set, bitno + 1); bitset_resize (pos_set, bitno + 1);
bitset_set (pos_set, bitno); bitset_set (pos_set, bitno);
} }