fzy.lua: do byte comparision instead string ones

This are char comparisions, but in lua they are expressed as full string
compare. Compare as bytes instead, this is significantly faster,
especially with luajit compiled code.

player/lua/fzy.lua

@@ -36,6 +36,19 @@ local MATCH_MAX_LENGTH = 1024
 
 local fzy = {}
 
+local byte = string.byte
+
+local CHAR_SLASH      = byte("/")
+local CHAR_BACKSLASH  = byte("\\")
+local CHAR_DASH       = byte("-")
+local CHAR_UNDERSCORE = byte("_")
+local CHAR_SPACE      = byte(" ")
+local CHAR_DOT        = byte(".")
+local CHAR_A          = byte("A")
+local CHAR_Z          = byte("Z")
+local CHAR_a          = byte("a")
+local CHAR_z          = byte("z")
+
 -- Check if `needle` is a subsequence of the `haystack`.
 --
 -- Usually called before `score` or `positions`.
@@ -66,32 +79,24 @@ function fzy.has_match(needle, haystack, case_sensitive)
   return true
 end
 
-local function is_lower(c)
-  return c:match("%l")
-end
-
-local function is_upper(c)
-  return c:match("%u")
-end
-
 local function precompute_bonus(haystack)
   local match_bonus = {}
-
-  local last_char = "/"
-  for i = 1, string.len(haystack) do
-    local this_char = haystack:sub(i, i)
-    if last_char == "/" or last_char == "\\" then
-      match_bonus[i] = SCORE_MATCH_SLASH
-    elseif last_char == "-" or last_char == "_" or last_char == " " then
-      match_bonus[i] = SCORE_MATCH_WORD
-    elseif last_char == "." then
-      match_bonus[i] = SCORE_MATCH_DOT
-    elseif is_lower(last_char) and is_upper(this_char) then
-      match_bonus[i] = SCORE_MATCH_CAPITAL
-    else
-      match_bonus[i] = 0
+  local last_char = CHAR_SLASH
+  for i = 1, #haystack do
+    local this_char = byte(haystack, i)
+    local bonus = 0
+    if last_char == CHAR_SLASH or last_char == CHAR_BACKSLASH then
+      bonus = SCORE_MATCH_SLASH
+    elseif last_char == CHAR_DASH or last_char == CHAR_UNDERSCORE or last_char == CHAR_SPACE then
+      bonus = SCORE_MATCH_WORD
+    elseif last_char == CHAR_DOT then
+      bonus = SCORE_MATCH_DOT
+    elseif last_char >= CHAR_a and last_char <= CHAR_z and
+           this_char >= CHAR_A and this_char <= CHAR_Z then
+      bonus = SCORE_MATCH_CAPITAL
     end
 
+    match_bonus[i] = bonus
     last_char = this_char
   end