Patch: Remove unneeded double operation in libstdc++-v3/src/c++17/fs_path.cc

[Jonathan Wakely]

On 18/12/23 09:36 +0100, Martin Küttler wrote:
>This is a small change to libstdc++ which does not change any behavior.

Please CC the libstdc++@gcc.gnu.org list on all libstdc++ patches, as
documented at https://gcc.gnu.org/lists.html

Otherwise I won't see the patches unless I happen to glance at the
gcc-patches archive by chance.

>This change has two, ihmo positive, implications:
>
> - The implicit conversion from double to int is avoided (Avoiding a
>   warning).

I don't see any warning here. What do you see?

> - No floating point number is used at all, which could be significant
>   in some scenarios.

Yes, it seems worth doing for this reason. I'll test+push the patch,
thanks.

Looking at path::_List::reserve now, we probably also want to avoid
overflow. Although a path with INT_MAX/1.5 components seems
implausible for 32-bit and 64-bit targets, it could be a problem for
16-bit targets. I'll take care of that too.

>------------
>
>diff --git a/libstdc++-v3/src/c++17/fs_path.cc b/libstdc++-v3/src/c++17/fs_path.cc
>index d65b5482e8b..b47ed0aa7aa 100644
>--- a/libstdc++-v3/src/c++17/fs_path.cc
>+++ b/libstdc++-v3/src/c++17/fs_path.cc
>@@ -447,8 +447,9 @@ path::_List::reserve(int newcap, bool exact = false)
>
>   if (curcap < newcap)
>     {
>-      if (!exact && newcap < int(1.5 * curcap))
>-       newcap = 1.5 * curcap;
>+      const int nextcap = curcap + curcap / 2;
>+      if (!exact && newcap < nextcap)
>+       newcap = nextcap;
>
>       void* p = ::operator new(sizeof(_Impl) + newcap * sizeof(value_type));
>       std::unique_ptr<_Impl, _Impl_deleter> newptr(::new(p) _Impl{newcap});