Why does formatting a number round differently in LuaJIT vs. Lua? - lua

Using string.format() (which supposedly defers to C's sprintf())) to format a number in LuaJIT rounds differently than every other Lua interpreter I've tried:
$ lua -v
Lua 5.4.1 Copyright (C) 1994-2020 Lua.org, PUC-Rio
$ lua -e 'print(string.format("%.4f", 32.90625))'
32.9062
$ luajit -v
LuaJIT 2.1.0-beta3 -- Copyright (C) 2005-2020 Mike Pall. http://luajit.org/
$ luajit -e 'print(string.format("%.4f", 32.90625))'
32.9063
Why does this happen and how can I‌ make it stop? I'd like to tell LuaJIT to round the same direction every other Lua interpreter does.

Related

Cannot install FFI library for Lua/LuaJIT

I have already correctly installed Lua, LuaJIT and Luarocks (I can run each of them in the terminal without any errors too). I'm trying to run the command luarocks install luaffi but it is returning an error
Error: No results matching query were found for Lua 5.4
To check if it is available for other Lua versions, use --check-lua-versions.
So I tried running luarocks install luaffi --check-lua-versions which also returns the following:
Checking if available for other Lua versions...
Checking for Lua 5.1...
Checking for Lua 5.2...
Checking for Lua 5.3...
Error: No results matching query were found for Lua 5.4.
luaffi is not available for any Lua versions. "
I'm completely lost, I cannot use ffi in my code because of this (It returns module "ffi" not found).
After the build (See: https://github.com/zhaozg/lua-ffi ) you can use Lua 5.1 to test it.
€ cat luajit_sleep.lua
--[[
Lua JIT ffi Example - Implementing a Lua sleep() function from C
]]
local ffi = require("ffi")
ffi.cdef[[void Sleep(int ms); int poll(struct pollfd *fds, unsigned long nfds, int timeout);]]
local sleep
if ffi.os == "Windows" then
function sleep(s) ffi.C.Sleep(s*1000) end
else
function sleep(s) ffi.C.poll(nil, 0, s*1000) end
end
return sleep
€ /bin/lua
Lua 5.1.5 Copyright (C) 1994-2012 Lua.org, PUC-Rio
> sleep = require('luajit_sleep')
> sleep(1) -- CPU friendly sleep() function :-)
It uses (lsof | grep lua)...
/usr/local/lib/lua/5.1/ffi.so
EDIT - Found the Command to install: https://luarocks.org/modules/colesbury/luaffi
Do: luarocks install --server=https://luarocks.org/dev luaffi --verbose
Also goes to...
os.execute: chmod '0755' '/usr/local/lib/lua/5.1/ffi.so'
Results: 1
1 (number): 0
luaffi scm-1 is now installed in /usr/local (license: BSD)

Why -l option in lua interpreter acts strangely?

You can execute a sequence of chunks by giving them all as arguments
to the stand-alone interpreter, with the -l option. For instance, if
you have a file a with a single statement x=1 and another file b with
the statement print(x), the command line
prompt> lua -la -lb
will run the chunk in a, then the one in b, which will print the
expected 1.
The above is from the following link: https://www.lua.org/pil/1.1.html. Yet, when I was trying it out, I got a syntax error.
So, in file a.lua, I have only one line, which is a=1. Then in file b.lua, I have also only one line print("the value of a is:",a) . Then,
:~$ lua -i -la -lb
Lua 5.2.4 Copyright (C) 1994-2015 Lua.org, PUC-Rio
the value of a is: true
>
:~$
:~$ lua -la -lb
the value of a is: true
Lua 5.2.4 Copyright (C) 1994-2015 Lua.org, PUC-Rio
>
Why did it print out "the value of a is: true"? rather than "the value of a is: 1"?
Any comments are greatly appreciated.
The error is because you are use a = 1 in your file a.lua, unlike in the example where a.lua contains x = 1 and b.lua contains print(x).
Using a rather then x means your using the same a variable being written to when -la completes, changing it to true.
This happens because the option -l name is equal to name = require("name"). When require completes, on a file that returns no result to it, require will return true.
your command lua -la -lb would look something like this to lua:
a = require("a") --this returning true after it completes
b = require("b") --this printing the value of `a` which will always be `true`
Sources:
Similar question answered on Lua-Users: command-line -l option issue
Egor Skriptunoff's Comment on this question

Luac: read version 1280.1; expected at most 80.1

I try to load a .lc file that I compiled with luac beforehand:
print("Hello World!")
and
luac -o helloworld.lc helloworld.lua
in order to get the compilation. However, as I am importing that module I am getting:
\lua\ai\helloworld.lc too new: read version 1280.1; expected at most 80.1
This is my luac -v
E:\lua\lua-5.0.3\bin>luac -v
Lua 5.0.3 Copyright (C) 1994-2006 Tecgraf, PUC-Rio
The game I am modding is actually using Lua 5.0 which is why I don't really understand why I am seeing this error..

Is this a bug with os.date in Lua?

$ lua -v -e "print(os.date('%l'))"
Lua 5.2.2 Copyright (C) 1994-2013 Lua.org, PUC-Rio
lua: (command line):1: bad argument #1 to 'date' (invalid conversion specifier '%l')
stack traceback:
[C]: in function 'date'
(command line):1: in main chunk
[C]: in
If so, where am I supposed to submit a bug report?
It's not a bug in Lua. os.date uses format, as described by strftime C function provided by your compiler (I mean the compiler that Lua was compiled with). It is known that some compilers (MSVC, for instance, which just outright crashes when provided with certain patterns) do not provide all patterns.

Create a new file in Lua/LuaFileSystem

I've looked over the Lua & LuaFileSystem Docs and have yet to find a way to create a new file, I also scouted around on here but to the same end.
As a note, the solution I'm looking for has to be OS neutral to ensure portability, but I'm happy to get different answers for different systems.
Example (writing "Hello World" into test.txt):
$ lua
Lua 5.1.4 Copyright (C) 1994-2008 Lua.org, PUC-Rio
> file = io.open("test.txt", "w")
> file:write("Hello World")
> file:close()
> ^D
$ cat test.txt
Hello World
See also: Lua IO tutorial

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