#24: non-equivalence of equal Hash key strings
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Reporter: pmichaud | Owner:
Type: bug | Status: new
Priority: major | Milestone:
Component: core | Version:
Severity: medium | Keywords:
Lang: perl6 | Patch:
Platform: |
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Comment(by pmichaud):
I worked on this bug a bit, hoping to get Rakudo to use fixed-width
strings for more of its processing. In r39282 I made a change to
src/hash.c:205 that changes
{{{
if (s1->hashval != s2->hashval)
return 1;
}}}
to
{{{
if (s1->charset == s2->charset && s1->hashval != s2->hashval)
return 1;
}}}
The original assumed that different string hashvals automatically implied
logically unequal strings, but this holds only if the strings are from the
same charset. The above change causes the original test script to pass.
But now there's a different failure -- somehow in larger hashes logically
equivalent hash keys sometimes end up as non-equivalent. Here's a test
program (added to t/op/stringu.t in r39284):
{{{
$ cat x.pir
.sub 'main'
.local string str0, str1
str0 = unicode:"infix:\u00b1"
str1 = iso-8859-1:"infix:\xb1"
.local pmc hash
hash = new 'Hash'
hash[str0] = 'hello'
$I0 = 0
fill_loop:
unless $I0 < 200 goto fill_done
inc $I0
$S0 = $I0
$S0 = concat 'infix:', $S0
hash[$S0] = 'hello'
goto fill_loop
fill_done:
$I0 = iseq str0, str1
print "iseq str0, str1 => "
say $I0
$S0 = hash[str0]
$S1 = hash[str1]
$I0 = iseq $S0, $S1
print "iseq hash[str0], hash[str1] => "
say $I0
say $S0
say $S1
.end
$ ./parrot x.pir
iseq str0, str1 => 1
iseq hash[str0], hash[str1] => 0
hello
$
}}}
This test is very sensitive to the size of the hash -- in fact, the
failure only appears when the hash has more than 192 entries. I'm not
sure of the significance of the 192 here, but I suspect it has something
to do with bucket and/or key management in hashes. (Change the "200" to
"191" in the test script above and it produces the correct output.)
AFAICT this problem is the only significant blocker to Rakudo being able
to run a significant number of spectests using fixed-width (iso-8859-1)
strings, which will reduce the overall "make spectest" time by about 20%.
Thanks,
Pm
--
Ticket URL: <https://trac.parrot.org/parrot/ticket/24#comment:4>
Parrot <https://trac.parrot.org/parrot/>
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