reimplement vi0 and helper functions so that they are likely faster (vi0 bring cursor to start of current line; before, this was done by checking each character in the string backwards, but now it is done by looking at the line metadata, which is faster for us by some constant factor)

fcore/cursor.sml

@@ -1,15 +1,41 @@
 structure Cursor =
 struct
-  fun helpVi0 (strPos, str, absIdx, strTl, lineTl) =
+  (* returns absolute index of previous line break in string *)
-    if strPos < 0 then
+  fun helpVi0 (absIdx, stl, ltl) =
-      case (strTl, lineTl) of
+    case (stl, ltl) of
-        (shd :: stl, lhd :: ltl) =>
+      (shd :: stl, lhd :: ltl) =>
-          helpVi0 (String.size shd - 1, shd, absIdx, stl, ltl)
+        if Vector.length lhd > 0 then
-      | (_, _) => 0
+          let
+            val startAbsIdx = absIdx - String.size shd
+            val lineIdx = Vector.sub (lhd, Vector.length lhd - 1)
+          in
+            (* found lineIdx. 
+             * Need to make sure we follow cursor-on-linebreak rule:
+             * If line break is preceded by non-line break char,
+             * then increment by 1.
+             * *)
+             startAbsIdx + lineIdx + 1
+          end
+        else
+          helpVi0 (absIdx - String.size shd, stl, ltl)
+    | (_, _) => 0
+
+  fun startVi0 (strPos, shd, lhd, absIdx, stl, ltl) =
+    if String.sub (shd, strPos) = #"\n" then
+      absIdx
     else
-      case String.sub (str, strPos) of
+      if Vector.length lhd > 0 then
-        #"\n" => absIdx + 1
+        if Vector.sub (lhd, 0) < strPos then
-      | _ => helpVi0 (strPos - 1, str, absIdx - 1, strTl, lineTl)
+          let
+            val linePos = BinSearch.equalOrLess (strPos - 1, lhd)
+            val lineIdx = Vector.sub (lhd, linePos)
+          in
+            absIdx - strPos + lineIdx + 1
+          end
+        else
+          helpVi0 (absIdx - strPos, stl, ltl)
+      else
+        helpVi0 (absIdx - strPos, stl, ltl)
 
   fun vi0 (lineGap: LineGap.t, cursorIdx) =
     let
@@ -25,14 +51,8 @@ struct
           in
             if strIdx < String.size strHd then
               (* strIdx is in this string *)
-              if String.sub (strHd, strIdx) = #"\n" then
+              startVi0
-                (* don't need to do anything if we are already at newline;
+                (strIdx, strHd, lnHd, cursorIdx, leftStrings, leftLines)
-                 * just return current cursorIdx *)
-                cursorIdx
-              else
-                (* not at newline so start iterating *)
-                helpVi0 
-                  (strIdx - 1, strHd, cursorIdx - 1, leftStrings, leftLines)
             else
               (* strIdx must be in the strTl *)
               (case (strTl, lnTl) of
@@ -40,18 +60,14 @@ struct
                    let
                      val strIdx = strIdx - String.size strHd
                    in
-                     if String.sub (nestStrHd, strIdx) = #"\n" then
+                     startVi0
-                       (* already at linebreak so return same cursorIdx *)
+                       ( strIdx
-                       cursorIdx
+                       , nestStrHd
-                     else
+                       , nestLnHd
-                       (* not in linebreak *)
+                       , cursorIdx
-                       helpVi0
+                       , strHd :: leftStrings
-                         ( strIdx - 1
+                       , lnHd :: leftLines
-                         , nestStrHd
+                       )
-                         , cursorIdx - 1
-                         , strHd :: leftStrings
-                         , lnHd :: leftLines
-                         )
                    end
                | (_, _) => cursorIdx)
           end
@@ -541,8 +557,8 @@ struct
               (* graphical-chr -> \n -> \n 
                * so go to beginning of line, 
                * starting from graphical-chr *)
-              helpVi0
+              startVi0
-                (strIdx - 2, shd, cursorIdx - 2, leftStrings, leftLines)
+                (strIdx - 2, shd, lhd, cursorIdx - 2, leftStrings, leftLines)
           else
             (* strIdx - 2 is in leftStrings *)
             case (leftStrings, leftLines) of
@@ -555,8 +571,8 @@ struct
                 (* graphical-chr -> \n -> \n 
                  * so go to beginning of line, 
                  * starting from graphical-chr *)
-                 helpVi0
+                 startVi0
-                   (String.size lshd - 1, lshd, cursorIdx - 2, lstl, lltl)
+                   (String.size lshd - 1, lshd, llhd, cursorIdx - 2, lstl, lltl)
             | (_, _) =>
                 (* nothing to the left, so we are at start of buffer *)
                 0
@@ -564,7 +580,8 @@ struct
           (* ? -> graphical-chr -> \n 
            * Don't expect this case to happen
            * but if it does, go to start of line. *)
-           helpVi0 (strIdx - 1, shd, cursorIdx - 1, leftStrings, leftLines)
+           startVi0 
+             (strIdx - 1, shd, lhd, cursorIdx - 1, leftStrings, leftLines)
       else
         (* strIdx - 1 is in leftStrings *)
         case (leftStrings, leftLines) of
@@ -578,8 +595,8 @@ struct
                   cursorIdx - 1
                 else
                   (* graphical-chr -> \n -> \n *)
-                  helpVi0
+                  startVi0
-                    (String.size lshd - 2, lshd, cursorIdx - 2, lstl, lltl)
+                    (String.size lshd - 2, lshd, llhd, cursorIdx - 2, lstl, lltl)
               else
                 (* cursorIdx - 2 is in lstl *)
                 (case (lstl, lltl) of
@@ -589,12 +606,13 @@ struct
                       cursorIdx - 1
                     else
                       (* graphical-chr -> \n -> \n *)
-                      helpVi0
+                      startVi0
-                        (String.size stlhd - 1, stlhd, cursorIdx - 2, lstl, lltl)
+                        (String.size stlhd - 1, stlhd, ltlhd, cursorIdx - 2, lstl, lltl)
                 | (_, _) => 0)
             else
               (* ? -> graphical-chr -> \n *)
-               helpVi0 (String.size lshd - 1, lshd, cursorIdx - 1, leftStrings, leftLines)
+              startVi0
+                (String.size lshd - 1, lshd, llhd, cursorIdx - 1, leftStrings, leftLines)
         | (_, _) =>
             (* leftStrings is empty so go to start of buffer *)
             0
@@ -1636,8 +1654,9 @@ struct
             (case (leftStrings, leftLines) of
               (lshd :: lstl, llhd :: lltl) =>
                 let
-                  val result = helpVi0 
+                  val result = 
-                    (String.size lshd - 1, lshd, bufferIdx - 1, lstl, lltl)
+                    startVi0
+                      (String.size lshd - 1, lshd, llhd, bufferIdx - 1, lstl, lltl)
                 in
                   if result = bufferIdx then
                     bufferIdx - 1