From 16fd813e55280b9aa95cff788b0099b776a75c74 Mon Sep 17 00:00:00 2001
From: letouzey
Date: Fri, 7 Dec 2012 16:39:48 +0000
Subject: Ideutils: simpler conversion from byte offset to utf8 char offset

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16042 85f007b7-540e-0410-9357-904b9bb8a0f7
---
 ide/ideutils.ml | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/ide/ideutils.ml b/ide/ideutils.ml
index c376df99bc..e5d5ebaa88 100644
--- a/ide/ideutils.ml
+++ b/ide/ideutils.ml
@@ -29,23 +29,17 @@ let set_location = ref  (function s -> failwith "not ready")
 
 let get_insert input_buffer = input_buffer#get_iter_at_mark `INSERT
 
+(** A utf8 char is either a single byte (ascii char, 0xxxxxxx)
+    or multi-byte (with a leading byte 11xxxxxx and extra bytes 10xxxxxx) *)
+
+let is_extra_byte c = ((Char.code c) lsr 6 = 2)
+
 let byte_offset_to_char_offset s byte_offset =
-  if (byte_offset < String.length s) then begin
-    let count_delta = ref 0 in
-    for i = 0 to byte_offset do
-      let code = Char.code s.[i] in
-      if code >= 0x80 && code < 0xc0 then incr count_delta
-    done;
-    byte_offset - !count_delta
-  end
-  else begin
-    let count_delta = ref 0 in
-    for i = 0 to String.length s - 1 do
-      let code = Char.code s.[i] in
-      if code >= 0x80 && code < 0xc0 then incr count_delta
-    done;
-    byte_offset - !count_delta
-  end
+  let extra_bytes = ref 0 in
+  for i = 0 to min byte_offset (String.length s - 1) do
+    if is_extra_byte s.[i] then incr extra_bytes
+  done;
+  byte_offset - !extra_bytes
 
 let print_id id =
   Minilib.log ("GOT sig id :"^(string_of_int (Obj.magic id)))
-- 
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