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* fns.c: Don't overflow int when computing a list length.

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(Fsafe_length): Return a float if the value is not representable
as a fixnum.  This shouldn't happen except in contrived situations.
Use same QUIT_COUNT_HEURISTIC as Flength now does.
This commit is contained in:
Paul Eggert 2011-06-14 15:32:12 -07:00
parent 00c604f263
commit e6966cd635
2 changed files with 40 additions and 16 deletions
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14
src/ChangeLog
View file

@ -1,10 +1,14 @@
2011-06-14 Paul Eggert <eggert@cs.ucla.edu>
* fns.c (Flength): Don't overflow int when computing a list length.
Use EMACS_INT, not int, to avoid unwanted truncation on 64-bit hosts.
Check for QUIT every 1024 entries rather than every other entry;
that's faster and is responsive enough. Report an error instead of
overflowing an integer.
* fns.c: Don't overflow int when computing a list length.
* fns.c (QUIT_COUNT_HEURISTIC): New constant.
(Flength, Fsafe_length): Use EMACS_INT, not int, to avoid unwanted
truncation on 64-bit hosts. Check for QUIT every
QUIT_COUNT_HEURISTIC entries rather than every other entry; that's
faster and is responsive enough.
(Flength): Report an error instead of overflowing an integer.
(Fsafe_length): Return a float if the value is not representable
as a fixnum. This shouldn't happen except in contrived situations.
* alloc.c: Check that resized vectors' lengths fit in fixnums.
(header_size, word_size): New constants.

42
src/fns.c
View file

@ -99,6 +99,10 @@ Other values of LIMIT are ignored. */)
return lispy_val;
}
/* Heuristic on how many iterations of a tight loop can be safely done
before it's time to do a QUIT. This must be a power of 2. */
enum { QUIT_COUNT_HEURISTIC = 1 << 16 };
/* Random data-structure functions */
DEFUN ("length", Flength, Slength, 1, 1, 0,
@ -128,7 +132,7 @@ To get the number of bytes, use `string-bytes'. */)
do
{
++i;
if ((i & ((1 << 10) - 1)) == 0)
if ((i & (QUIT_COUNT_HEURISTIC - 1)) == 0)
{
if (MOST_POSITIVE_FIXNUM < i)
error ("List too long");
@ -159,22 +163,38 @@ it returns 0. If LIST is circular, it returns a finite value
which is at least the number of distinct elements. */)
(Lisp_Object list)
{
Lisp_Object tail, halftail, length;
int len = 0;
Lisp_Object tail, halftail;
double hilen = 0;
uintmax_t lolen = 1;
if (! CONSP (list))
return 0;
/* halftail is used to detect circular lists. */
halftail = list;
for (tail = list; CONSP (tail); tail = XCDR (tail))
for (tail = halftail = list; ; )
{
if (EQ (tail, halftail) && len != 0)
tail = XCDR (tail);
if (! CONSP (tail))
break;
len++;
if ((len & 1) == 0)
halftail = XCDR (halftail);
if (EQ (tail, halftail))
break;
lolen++;
if ((lolen & 1) == 0)
{
halftail = XCDR (halftail);
if ((lolen & (QUIT_COUNT_HEURISTIC - 1)) == 0)
{
QUIT;
if (lolen == 0)
hilen += UINTMAX_MAX + 1.0;
}
}
}
XSETINT (length, len);
return length;
/* If the length does not fit into a fixnum, return a float.
On all known practical machines this returns an upper bound on
the true length. */
return hilen ? make_float (hilen + lolen) : make_fixnum_or_float (lolen);
}
DEFUN ("string-bytes", Fstring_bytes, Sstring_bytes, 1, 1, 0,