bitwise operations on Android

perrochon · April 2020

It's me again... I am sure this has been seen before, but I couldn't find a discussion.

I have tiled generated maps and load them into a Gideros TileMap. Tiled uses the ID of the tile to indicate rotation by setting high bits, which have to be read from the ID, then removed from the ID, then passed on to TileMap. There is code discussing this at tiled, and in the gideros wiki

http://doc.mapeditor.org/en/stable/reference/tmx-map-format/#tile-flipping
https://wiki.giderosmobile.com/index.php/CBump_Template

My problem is that the code similar to the one on that page works in the player on Windows, but not when deployed on Android (Pixel 3)

Here is what I am doing

local FLIPPED_HORIZONTALLY_FLAG = 0x80000000;
local FLIPPED_VERTICALLY_FLAG   = 0x40000000;
local FLIPPED_DIAGONALLY_FLAG   = 0x20000000;
 
--  
-- for each tile ID gid
 
-- Read flipping flags
flipHor = gid & FLIPPED_HORIZONTALLY_FLAG
flipVer = gid & FLIPPED_VERTICALLY_FLAG
flipDia = gid & FLIPPED_DIAGONALLY_FLAG
 
-- Convert flags to gideros style
if(flipHor ~= 0) then flipHor = TileMap.FLIP_HORIZONTAL end
if(flipVer ~= 0) then flipVer = TileMap.FLIP_VERTICAL end
if(flipDia ~= 0) then flipDia = TileMap.FLIP_DIAGONAL end
 
-- Clear the flags from gid so other information is healthy
 
local oldgid = gid -- debug
 
gid = gid & ~ (
FLIPPED_HORIZONTALLY_FLAG |
FLIPPED_VERTICALLY_FLAG |
FLIPPED_DIAGONALLY_FLAG
)
 
local newgid = gid -- debug
 
if oldgid ~= newgid then
  print("flipped gid", oldgid, newgid)
end

If I run this in the Windows player, it works as expected and the output looks about like this

flipped gid	1610612812	76
flipped gid	2684354637	77

If I run it on the Android Gideros player, it flips all the IDs to 0

flipped gid	1610612812	0
flipped gid	77	0
flipped gid	13	0
flipped gid	2684354637	0

Looking for documentation of bitwise operations across different OS? Different architecture? I am pretty sure that my windows box and android are both 64 bit. How do I have to do this so it works across all platforms?

perrochon · April 2020

edit: I got a smaller sample below

MoKaLux · April 2020

maybe you need to add the Bitop plugin to your project for it to work on android?
As hgy29 said: the gideros player includes all the plugins but when you export you need to add the plugins yourself.

perrochon · April 2020

@MoKaLux thanks for the tip. Doesn't seem to help. I distilled it down to very short code. It doesn't matter if I include the bitop plugin or not (ignore the %x in the string)

It seems to be using unsigned integers on windows, and signed integers on android for bitwise. If you print out B32 in gideros it's 2147483648 both ways, but maybe for bitwise, the underlying C++ code somewhere does the shift thinking they are signed on Android.

function f(i) return string.format("%x", i) end
 
local B1  = 0b00000000000000000000000000000001
local B31 = 0b01000000000000000000000000000000
local B32 = 0b10000000000000000000000000000000
 
print ("B1", f(B1))
print ("B31", f(B31))
print ("B32", f(B32))
 
print ("B1|B31", f(B1|B31))
print ("B1|B32", f(B1|B32))
 
print ("B31>>1", f(B31>>1))
print ("B32>>1", f(B32>>1))

Windows

B1	1
B31	40000000
B32	80000000
B1|B31	40000001
B1|B32	80000001
B31>>1	20000000
B32>>1	c0000000

Android

B1	1
B31	40000000
B32	80000000
B1|B31	40000001
B1|B32	7fffffff
B31>>1	20000000
B32>>1	3fffffff

MoKaLux · April 2020

on my side with your code
windows
Uploading finished.
B1 %x 1
B31 %x 40000000
B32 %x 80000000
B1|B31 %x 40000001
B1|B32 %x 80000001

android
main.lua is uploading.
Uploading finished.
B1 %x 1
B31 %x 40000000
B32 %x 80000000
B1|B31 %x 40000001
B1|B32 %x 80000001

same!

Maybe your android player doesn't include the bitop plugin?
I have a big android player you can try:https://github.com/mokalux/gideros-player-for-android
Are you testing over wifi?

perrochon · April 2020

Interesting! I am testing over Wifi. How do I know if my player has the plugin? Wouldn't Gideros upload it if I include it in the project?

MoKaLux · April 2020

yes gideros will package the plugin on export but here you are not compiling for export, you are using the plugins of your android player over wifi.

perrochon · April 2020

Also, I'd like a solution to test for the top bit that is more cross platform, and doesn't require a specific player. Maybe the freedom from number types in Lua gets in the way here?

MoKaLux · April 2020

where did you get the android player apk? In the gideros installation folder, on google play https://play.google.com/store/apps/details?id=info.simart.gideros?
The lighter the apk the less plugins it has

Mine has almost all the plugins 26.3 Mb!
We could post an up to date android player somewhere here in the forum or in the wiki?

perrochon · April 2020

I think I got the player that came with the install. Sideloaded the APK.

MoKaLux · April 2020

I think the bitop plugin is not included in this apk. You can build your own if you want

perrochon · April 2020

(off-topic) I downloaded the player you linked to from the Play Store. But it doesn't show up in the drop down of Gideros Studio like the one from the Gideros installation folder does. How do I connect to the player from the play store? Can I?

MoKaLux · April 2020

that should work the same, have you uninstalled the old first? you may have launched to wrong one

rrraptor · April 2020

I have different results too, but with bitop plugin it is the same.

Windows:
=====================
B1	1
B31	1073741824
B32	2147483648
======= BitOp =======
B1|B31	1073741825
B1|B32	-2147483647
B31>>1	536870912
B32>>1	1073741824
====== Native? ======
B1|B31	1073741825
B1|B32	-2147483647
B31>>1	536870912
B32>>1	-1073741824
 
Android:
=====================
B1	1
B31	1073741824
B32	2147483648
======= BitOp =======
B1|B31	1073741825
B1|B32	-2147483647
B31>>1	536870912
B32>>1	1073741824
====== Native? ======
B1|B31	1073741825
B1|B32	2147483647
B31>>1	536870912
B32>>1	1073741823

require "bit"
 
local B1  = 1
local B31 = 0b01000000000000000000000000000000
local B32 = 0b10000000000000000000000000000000
print("=====================")
print("B1", B1)
print("B31", B31)
print("B32", B32)
print("======= BitOp =======")
print("B1|B31", bit.bor(B1,B31))
print("B1|B32", bit.bor(B1,B32))
print("B31>>1", bit.rshift(B31,1))
print("B32>>1", bit.rshift(B32,1))
 
print("====== Native? ======")
print("B1|B31", B1|B31)
print("B1|B32", B1|B32)
print("B31>>1", B31>>1)
print("B32>>1", B32>>1)

hgy29 · April 2020

Guys, remember that gideros uses lua 5.1, in which all numbers are floats, not integers. Depending on the platform FPU, you may get different results when you exceed that float mantissa resolution.
To overcome the issue with tiled, I first converted the tiled value to int64 in lua, and they applied bitwise ops on this 64 bit number.

perrochon · April 2020

Yes, I feared something like this is the answer. Nice that there is an int64 in Lua. Struggling a bit with the documentation, though.

http://docs.giderosmobile.com/reference/lua/int64#int64

So the code now looks like this for reading of the top bits

gid64 = int64.new(gid)
local flip = 0
if gid64[31] ~= gid64[28] then flip = flip | TileMap.FLIP_HORIZONTAL end
if gid64[30] ~= gid64[28] then flip = flip | TileMap.FLIP_VERTICAL end
if gid64[29] ~= gid64[28] then flip = flip | TileMap.FLIP_DIAGONAL end

I tried == 1 but that didn't equal. What do I compare it to? How do I figure out the type?

Then, to clear the top three bits I do this

gid64[31]=0
gid64[30]=0
gid64[29]=0
gid = gid64()

I think I want to put a number back into the gid, and not carry the gid64 forward. but tonumber(gid64) returns nil. is gid64() doing that?

hgy29 · April 2020

yes, () converts back to an int.
Here is an extract of my (ugly) code:

local tgid=int64.new(o.gid)
local tfliph,tflipv,tflipd=(tgid&#0x80000000)>#0,(tgid&#0x40000000)>#0,(tgid&#0x20000000)>#0
local tl=(tgid&#0x1FFFFFFF)()

perrochon · April 2020

It's not ugly, just very C++y :-)

perrochon · April 2020

And it's not even in Wirth Normal Form
(WNF: no variable can be shortened without generating conflict with another)

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