Pushed to trunk.
On Sat, 1 Jun 2024 at 11:26, Jonathan Wakely <jwak...@redhat.com> wrote:
>
> We get smaller code at all optimization levels by not creating a
> temporary object, just comparing lengths first and then using
> traits_type::compare. This does less work than calling substr then
> operator==.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/string_view (starts_with(basic_string_view)):
> Compare lengths first and then call traits_type::compare
> directly.
> ---
> libstdc++-v3/include/std/string_view | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/include/std/string_view
> b/libstdc++-v3/include/std/string_view
> index a7c5a126461..740aa9344f0 100644
> --- a/libstdc++-v3/include/std/string_view
> +++ b/libstdc++-v3/include/std/string_view
> @@ -385,7 +385,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> [[nodiscard]]
> constexpr bool
> starts_with(basic_string_view __x) const noexcept
> - { return this->substr(0, __x.size()) == __x; }
> + {
> + return _M_len >= __x._M_len
> + && traits_type::compare(_M_str, __x._M_str, __x._M_len) == 0;
> + }
>
> [[nodiscard]]
> constexpr bool
> --
> 2.45.1
>
