Faster blitting @ BB8/BBRGB32 when no processing is needed (#4847)

* Pickup the eponymous blitting performance tweaks from koreader/koreader-base#878
* Cleanup BitOpts usage (require & cache)
* Unify oddness checks (MOD -> AND)
* Enforce the native Portrait orientation on Kobo (except @ 16bpp, i.e., KSM w/ 8bpp swap disabled), to allow for faster blitting when unrotted.
* Switch CRe BB to 32BPP on color screens
* Minor cleanups

frontend/apps/reader/modules/readerrolling.lua

@@ -1,3 +1,4 @@
+local bit = require("bit")
 local Blitbuffer = require("ffi/blitbuffer")
 local ConfirmBox = require("ui/widget/confirmbox")
 local Device = require("device")
@@ -11,6 +12,8 @@ local Input = Device.input
 local Screen = Device.screen
 local T = require("ffi/util").template
 
+local band = bit.band
+
 --[[
     Rolling is just like paging in page-based documents except that
     sometimes (in scroll mode) there is no concept of page number to indicate
@@ -789,12 +792,12 @@ function ReaderRolling:_gotoPage(new_page, free_first_page)
     if self.ui.document:getVisiblePageCount() > 1 and not free_first_page then
         -- Ensure we always have the first of the two pages odd
         if self.odd_or_even_first_page == 1 then -- odd
-            if new_page % 2 == 0 then
+            if band(new_page, 1) == 0 then
                 -- requested page will be shown as the right page
                 new_page = new_page - 1
             end
         elseif self.odd_or_even_first_page == 2 then -- (or 'even' if requested)
-            if new_page % 2 == 1 then
+            if band(new_page, 1) == 1 then
                 -- requested page will be shown as the right page
                 new_page = new_page - 1
             end