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re PR libstdc++/40852 ([parallel-mode] parallel sort run time increases ~10 fold when vector size gets over ~4*10^9) 

2009-10-28  Johannes Singler  <singler@kit.edu>

        PR libstdc++/40852
        * include/parallel/multiseq_selection.h
        (multiseq_partition, multiseq_selection):  Avoid intermediate
        values exceeding the integer type range for very large inputs.

From-SVN: r153649
This commit is contained in:
Johannes Singler 2009-10-28 10:04:35 +00:00 committed by Johannes Singler
parent e095750ccb
commit d5948b2e42
2 changed files with 13 additions and 20 deletions
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7
libstdc++-v3/ChangeLog
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@ -1,3 +1,10 @@
2009-10-28 Johannes Singler <singler@kit.edu>
PR libstdc++/40852
* include/parallel/multiseq_selection.h
(multiseq_partition, multiseq_selection): Avoid intermediate
values exceeding the integer type range for very large inputs.
2009-10-16 Benjamin Kosnik <bkoz@redhat.com>
* include/c_compatibility/stdatomic.h: Include cstdatomic if

26
libstdc++-v3/include/parallel/multiseq_selection.h
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@ -183,9 +183,6 @@ namespace __gnu_parallel
// equality iff nmax = 2^k - 1.
l = (1ULL << r) - 1;
// From now on, including padding.
N = l * m;
for (int i = 0; i < m; i++)
{
a[i] = 0;
@ -210,7 +207,7 @@ namespace __gnu_parallel
if (n >= ns[i]) //sequence too short, conceptual infinity
sample.push_back(std::make_pair(S(i)[0] /*dummy element*/, i));
difference_type localrank = rank * m / N ;
difference_type localrank = rank / l;
int j;
for (j = 0; j < localrank && ((n + 1) <= ns[sample[j].second]); ++j)
@ -258,15 +255,11 @@ namespace __gnu_parallel
b[i] -= n + 1;
}
difference_type leftsize = 0, total = 0;
difference_type leftsize = 0;
for (int i = 0; i < m; i++)
{
leftsize += a[i] / (n + 1);
total += l / (n + 1);
}
difference_type skew = static_cast<difference_type>
(static_cast<uint64>(total) * rank / N - leftsize);
difference_type skew = rank / (n + 1) - leftsize;
if (skew > 0)
{
@ -429,9 +422,6 @@ namespace __gnu_parallel
// equality iff nmax = 2^k - 1
l = pow2(r) - 1;
// From now on, including padding.
N = l * m;
for (int i = 0; i < m; ++i)
{
a[i] = 0;
@ -458,7 +448,7 @@ namespace __gnu_parallel
if (n >= ns[i])
sample.push_back(std::make_pair(S(i)[0] /*dummy element*/, i));
difference_type localrank = rank * m / N ;
difference_type localrank = rank / l;
int j;
for (j = 0; j < localrank && ((n + 1) <= ns[sample[j].second]); ++j)
@ -496,15 +486,11 @@ namespace __gnu_parallel
b[i] -= n + 1;
}
difference_type leftsize = 0, total = 0;
difference_type leftsize = 0;
for (int i = 0; i < m; ++i)
{
leftsize += a[i] / (n + 1);
total += l / (n + 1);
}
difference_type skew = ((unsigned long long)total * rank / N
- leftsize);
difference_type skew = rank / (n + 1) - leftsize;
if (skew > 0)
{