From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: "François Dumont" <frs.dumont@gmail.com>
Cc: "libstdc++@gcc.gnu.org" <libstdc++@gcc.gnu.org>,
gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Enhance unordered container merge
Date: Sun, 14 Nov 2021 23:25:32 +0000 [thread overview]
Message-ID: <CAH6eHdTh1Ja0OtaK_Yo-5rPw6hHAfMa8qR0hxsJi_2CWLmgVMQ@mail.gmail.com> (raw)
In-Reply-To: <fd621d0f-b217-97cc-3428-e3a709a4f259@gmail.com>
On Sun, 14 Nov 2021 at 13:31, François Dumont via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> libstdc++: Unordered containers merge re-use hash code.
>
> When merging between 2 unordered containers with same hasher we can
> re-use
> the cached hash code if any.
Instead of introducing the _ReuseOrComputeHash type, wouldn't it be
simpler to just overload _M_hash_code?
// Same hash function, use the cached hash code.
__hash_code
_M_hash_code(const _Hash&,
const _Hash_node_value<_Value, true>& __n) const
{ return __n._M_hash_code; }
// Compute hash code using a different hash function, _H2
template<typename _H2>
__hash_code
_M_hash_code(const _H2&,
const _Hash_node_value<_Value, __cache_hash_code>& __n) const
{ return this->_M_hash_code(_ExtractKey{}(__n._M_v()); }
The first overload is more specialized, so will be chosen when the
first argument is the same type as _Hash and the cache_has_code
boolean is true.
next prev parent reply other threads:[~2021-11-14 23:25 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-14 13:29 François Dumont
2021-11-14 23:25 ` Jonathan Wakely [this message]
2021-11-15 6:00 ` François Dumont
2021-11-15 9:10 ` Jonathan Wakely
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