[libstdc++/71500] make back reference work with icase

[Jonathan Wakely]

On 18/09/17 10:58 -0700, Tim Shen via libstdc++ wrote:
>On Mon, Sep 18, 2017 at 10:26 AM, Jonathan Wakely <jwakely@redhat.com> wrote:
>>> We need to rewrite this to check the lengths are equal first, and then
>>> call the 3-argument version of std::equal.
>>>
>>> Alternatively, we could move the implementation of the C++14
>>> std::equal overloads to __equal and make that available for C++11.
>>> I'll try that.
>>
>>
>> Here's a proof of concept patch for that. It's a bit ugly.
>
>Instead of having iterator tags in the interface, we can probe the
>random-access-ness inside __equal4/__equal4_p, can't we? It's similar
>to the existing "if (_RAIters()) { ... }".
>
>I'd expect the patches to be renaming the current implementations and
>adding wrappers, instead of adding new implementations.

Well I decided to split the existing functions up and use tag
dispatching, which is conceptually cleaner anyway. But as the
RandomAccessIterator version doesn't need any operations that aren't
valid for other categories, it's not strictly necessary. The tag
dispatching version should generate slightly smaller code for
unoptimized builds, but that's not very important.

Here's the patch doing it as you suggest. We can't call the new
functions __equal because t hat name is already taken by a helper
struct, hence __equal4.

Do you prefer this version?


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