[PATCH][libstdc++-v3 parallel mode] Get rid of hard-coded ints [was: Re: ints in parallel code]

[Johannes Singler]

Paolo Carlini wrote:
> Hi,
>> All the ints in multiway*.h address sequences, i. e. the functions are
>> limited to about 2^31 sequences.  The number of elements in these
>> sequences can be much higher.
>>
>> In principle, you are right, the sequences are passed using iterators,
>> and their difference could be 64 bits.  In practice, we are much further
>> away from having more than 2^31 sequences, than having more than 2^31
>> elements e. g. for sorting.
>>   
> Ok... Then, please help me summarizing the issue: if the user has a
> "data set" of 2^34 alements, will it be automatically "split", ie,
> processed, in chunks each < 2^31 elements?

No, for sorting, we will have p sequences, for p the number of threads
used.  That should be safe for an int anyway (omp_get_num_threads also
returns an int restrictions).
In general, the number of sequences is determined by the caller.

>> Anyway, do you want me to replace it with the appropriate
>> difference_type?  It might have performance implications, though.
>>   
> In general, if you want my opinion, these days unless you have *very
> clear* benchmarking numbers in front of you, it's always a very good
> idea to use the correct types, to begin with: if the difference can need
> 64 bits to be represented, use a 64-bit type.

The attached patch should get rid of most hard-coded occurrences of int.


Tested x86_64-unknown-linux-gnu: No regressions

Please approve for mainline.

2009-11-09  Johannes Singler  <singler@kit.edu>

        * include/parallel/multiway_merge.h (multiway_merge_*,
        __sequential_multiway_merge, parallel_multiway_merge):
	Replace int by appropriate difference_type (typedef to
	_SeqNumber) or _ThreadIndex.
        * include/parallel/multiseq_selection.h (multiseq_partition,
	multiseq_selection): Replace int by appropriate difference_type
	(typedef to _SeqNumber)
        * include/parallel/base.h (__get_max_threads): 	Replace int by
	_ThreadIndex.
        * include/parallel/balanced_quicksort.h
	(__qsb_local_sort_with_helping, __parallel_sort_qsb): Likewise.
        * include/parallel/set_operations.h (__parallel_set_operation):
	Likewise.
        * include/parallel/unique_copy.h (__parallel_unique_copy):
	Likewise.
        * include/parallel/multiway_mergesort.h (_SplitConsistently, 		
	parallel_sort_mwms_pu, parallel_sort_mwms): Likewise.
        * include/parallel/partial_sum.h
	(__parallel_partial_sum_linear): Likewise.
        * include/parallel/partition.h (__parallel_partition): 	Replace
	int by appropriate difference_type or _ThreadIndex.

Johannes
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