From d539e8fb896dff4ed1757eaf9a81d9385a709580 Mon Sep 17 00:00:00 2001
From: Maxime Coste <mawww@kakoune.org>
Date: Wed, 4 Dec 2019 22:00:31 +1100
Subject: [PATCH] Do not decode utf-8 when looking for regex next start

There is no need to decode as we know any non-ascii characters will
be treated as Other in the StartDesc.
---
 src/regex_impl.hh | 34 ++++++++++++++++------------------
 1 file changed, 16 insertions(+), 18 deletions(-)

diff --git a/src/regex_impl.hh b/src/regex_impl.hh
index e49c5186..13c48c09 100644
--- a/src/regex_impl.hh
+++ b/src/regex_impl.hh
@@ -235,8 +235,8 @@ public:
             }
             else if (start != config.end)
             {
-                const Codepoint cp = codepoint(start, config);
-                 if (not start_desc->map[cp < StartDesc::count ? cp : StartDesc::other])
+                const unsigned char c = forward ? *start : *utf8::previous(start, config.end);
+                 if (not start_desc->map[(c < StartDesc::count) ? c : StartDesc::other])
                     return false;
             }
         }
@@ -525,12 +525,21 @@ private:
     {
         while (start != config.end)
         {
-            const Codepoint cp = read_codepoint(start, config);
-            if (start_desc.map[(cp >= 0 and cp < StartDesc::count) ? cp : StartDesc::other])
+            static_assert(StartDesc::count <= 128, "start desc should be ascii only");
+            if constexpr (forward)
             {
-                forward ? utf8::to_previous(start, config.subject_begin)
-                        : utf8::to_next(start, config.subject_end);
-                return;
+                const unsigned char c = *start;
+                if (start_desc.map[(c < StartDesc::count) ? c : StartDesc::other])
+                    return;
+                utf8::to_next(start, config.end);
+            }
+            else
+            {
+                auto prev = utf8::previous(start, config.end);
+                const unsigned char c = *prev;
+                if (start_desc.map[(c < StartDesc::count) ? c : StartDesc::other])
+                    return;
+                start = prev;
             }
         }
     }
@@ -612,17 +621,6 @@ private:
                is_word(utf8::codepoint(pos, config.subject_end));
     }
 
-    static Codepoint read_codepoint(Iterator& it, const ExecConfig& config)
-    {
-        if (forward)
-            return utf8::read_codepoint(it, config.subject_end);
-        else
-        {
-            utf8::to_previous(it, config.subject_begin);
-            return utf8::codepoint(it, config.subject_end);
-        }
-    }
-
     static Codepoint codepoint(const Iterator& it, const ExecConfig& config)
     {
         return utf8::codepoint(forward ? it : utf8::previous(it, config.subject_begin),