git-gui: Optimize encoding name resolution using a lookup table.

Encoding menu construction does almost a hundred of encoding
resolutions, which with the old implementation led to a
small but noticeable delay.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Tested-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

diff --git a/lib/encoding.tcl b/lib/encoding.tcl
index b2ee38cc8aa11a453de19f4cfe0d07bf9940cd22..32668fc9c6debee6de9882719c305392c1e4791a 100644 (file)
--- a/lib/encoding.tcl
+++ b/lib/encoding.tcl
@@ -286,39 +286,63 @@ set encoding_groups {
        {"Symbol" Symbol Dingbats MacDingbats MacCentEuro}}
 }
 
+proc build_encoding_table {} {
+       global encoding_aliases encoding_lookup_table
+
+       # Prepare the lookup list; cannot use lsort -nocase because
+       # of compatibility issues with older Tcl (e.g. in msysgit)
+       set names [list]
+       foreach item [encoding names] {
+               lappend names [list [string tolower $item] $item]
+       }
+       set names [lsort -ascii -index 0 $names]
+       # neither can we use lsearch -index
+       set lnames [list]
+       foreach item $names {
+               lappend lnames [lindex $item 0]
+       }
+
+       foreach grp $encoding_aliases {
+               set target {}
+               foreach item $grp {
+                       set i [lsearch -sorted -ascii $lnames \
+                                       [string tolower $item]]
+                       if {$i >= 0} {
+                               set target [lindex $names $i 1]
+                               break
+                       }
+               }
+               if {$target eq {}} continue
+               foreach item $grp {
+                       set encoding_lookup_table([string tolower $item]) $target
+               }
+       }
+
+       foreach item $names {
+               set encoding_lookup_table([lindex $item 0]) [lindex $item 1]
+       }
+}
+
 proc tcl_encoding {enc} {
-    global encoding_aliases
-    set names [encoding names]
-    set lcnames [string tolower $names]
-    set enc [string tolower $enc]
-    set i [lsearch -exact $lcnames $enc]
-    if {$i < 0} {
-       # look for "isonnn" instead of "iso-nnn" or "iso_nnn"
-       if {[regsub {^(iso|cp|ibm|jis)[-_]} $enc {\1} encx]} {
-           set i [lsearch -exact $lcnames $encx]
+       global encoding_lookup_table
+       if {$enc eq {}} {
+               return {}
+       }
+       if {![info exists encoding_lookup_table]} {
+               build_encoding_table
        }
-    }
-    if {$i < 0} {
-       foreach l $encoding_aliases {
-           set ll [string tolower $l]
-           if {[lsearch -exact $ll $enc] < 0} continue
-           # look through the aliases for one that tcl knows about
-           foreach e $ll {
-               set i [lsearch -exact $lcnames $e]
-               if {$i < 0} {
-                   if {[regsub {^(iso|cp|ibm|jis)[-_]} $e {\1} ex]} {
-                       set i [lsearch -exact $lcnames $ex]
-                   }
+       set enc [string tolower $enc]
+       if {![info exists encoding_lookup_table($enc)]} {
+               # look for "isonnn" instead of "iso-nnn" or "iso_nnn"
+               if {[regsub {^(iso|cp|ibm|jis)[-_]} $enc {\1} encx]} {
+                       set enc $encx
                }
-               if {$i >= 0} break
-           }
-           break
        }
-    }
-    if {$i >= 0} {
-       return [lindex $names $i]
-    }
-    return {}
+       if {[info exists encoding_lookup_table($enc)]} {
+               return $encoding_lookup_table($enc)
+       } else {
+               return {}
+       }
 }
 
 proc force_path_encoding {path enc} {