[Bug libstdc++/22634] New: partial_sum is too constrained

["squell at alumina dot nl" <gcc-bugzilla at gcc dot gnu dot org>]

Say, we're running std::partial_sum, where the output type is 'wider' than
the input. E.g,

    char in_array[4] = { 96, 96, 96, 96 };
    int  out_array[4];

    partial_sum(in_array, in_array+4, out_array);

This "should" be:

    int out_array[4] = { 96, 96+96, 96+96+96, 96+96+96+96 };

This is a problem since partial_sum obviously uses an accumulator to hold
the intermediate result, but it uses the input iterator's value_type to
determine the type of the accumulator. So the result in the above case will
be an array with the values 96, -64, 32, -128 (with 8bit signed char).

More involved cases, where the input value_type and output_value type are
incompatible, won't even compile.

I have taken the partial_sum from bits/stl_numeric.h (distributed with DJGPP's
version of g++ 4.01) and produced a work-around solution for this which I
think works correctly and is portable. Note that I reformatted the code and
removed the "gxx" bits, so the attached code is intended as a concept only.

Summary; the solution uses template argument type deduction to determine the
type of accumulator to be used.

-- 
           Summary: partial_sum is too constrained
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: squell at alumina dot nl
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22634