Make genEventID 5x as fast

showIntAtBase wasn't inlined, so not specialised to Word64, so all the
arithmetic went via typeclasses (inluding a number of fromIntegral
@Word64 @Int, which went via Integer).

1 files changed, 11 insertions, 1 deletions

diff --git a/src/Index.hs b/src/Index.hs
index 148f314..5ac59be 100644
--- a/src/Index.hs
+++ b/src/Index.hs
@@ -4,6 +4,7 @@
 {-# LANGUAGE ViewPatterns #-}
 module Index (
   Index,
+  EventID,
   initIndex,
   indexGetEventsLinear,
   findEventIDLinear,
@@ -388,10 +389,19 @@ genEventID (YMDHMS (YMD y m d) (HMS hh mm ss)) off
       let cast :: Integral a => a -> Word64 ; cast = fromIntegral
           num = (((((cast off * 5000 + cast y) * 12 + cast (m - 1)) * 31 + cast (d - 1))
                   * 24 + cast hh) * 60 + cast mm) * 60 + cast ss
-      in T.pack ('a' : showIntAtBase 62 base62char num "")
+      in T.pack ('a' : showBase62 num "")
   where
     base62char = chr . fromIntegral . (base62alphabet `BS.index`)
     base62alphabet = BS.pack (map (fromIntegral . ord) (['0'..'9'] ++ ['A'..'Z'] ++ ['a'..'z']))
+    showBase62 :: Word64 -> ShowS
+    showBase62 topnum
+      | topnum == 0 = (base62char 0 :)
+      | otherwise = go topnum
+      where
+        go :: Word64 -> ShowS
+        go 0 = id
+        go n = let (q, r) = n `quotRem` 62
+               in go q . (base62char (fromIntegral @Word64 @Int r) :)
 
 -- >>> parseEventID "a5d9CtBVX"
 -- Just (YMDHMS (YMD 2026 4 7) (HMS 18 56 55),123)