From 482f97e79fc29ea2d61f1425b32564a668b51e1c Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Thu, 30 May 2024 20:36:42 +0100 Subject: [PATCH] libstdc++: Optimize std::basic_string_view::starts_with 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 a7c5a1264613..740aa9344f01 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 -- 2.47.2