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try using native bitwise operations without checking lua version #177

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try using native bitwise operations without checking lua version #177

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try using native bitwise operations without checking lua version
jprjr Nov 23, 2020
6c3c69c
bit: check for loadstring and use it if it exists
jprjr Nov 24, 2020
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27 changes: 18 additions & 9 deletions http/bit.lua
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Original file line number Diff line number Diff line change
Expand Up @@ -7,17 +7,26 @@ The bit operations are only done
This means we can ignore the differences between bit libraries.
]]

-- Lua 5.3 has built-in bit operators, wrap them in a function.
if _VERSION == "Lua 5.3" then
-- Use debug.getinfo to get correct file+line numbers for loaded snippet
local info = debug.getinfo(1, "Sl")
return assert(load(("\n"):rep(info.currentline+1)..[[return {
band = function(a, b) return a & b end;
bor = function(a, b) return a | b end;
bxor = function(a, b) return a ~ b end;
}]], info.source))()
-- Lua 5.1's load function doesn't support reading strings, only
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Use loadstring in 5.1?

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Yeah, I guess it's six of one, half-dozen of the other.

This could be replaced with something like "local l = load; if loadstring then l = loadstring"

I can switch to something like that if you prefer, let me know!

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I guess loadstring doesn't have a source argument; so load is best.

It annoys me a little that we don't use straight up load in newer versions of lua.
I just realised we already depend on compat-5.3 in lua 5.1, so how about:

local load = load
if _VERSION == "Lua 5.1" then
    load = require "compat53.module".load
end

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re: loadstring - in the docs they list the second parameter as chunk instead of source, but it's the same thing, loadstring should work and show the source filename as intended.

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See latest push, I just did local load = loadstring or load

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I don't want to use loadstring if load is available.

-- functions.
local function string_loader(str)
local sent = false
return function()
if sent then return nil end
sent = false
return str
end
end

-- Lua 5.3+ has built-in bit operators, wrap them in a function.
local info = debug.getinfo(1, "Sl")
local has_bitwise, bitwise = pcall(load(string_loader(("\n"):rep(info.currentline+1)..[[return {
band = function(a, b) return a & b end;
bor = function(a, b) return a | b end;
bxor = function(a, b) return a ~ b end;
}]]), info.source))
if has_bitwise then return bitwise end

-- The "bit" library that comes with luajit
-- also available for lua 5.1 as "luabitop": http://bitop.luajit.org/
local has_bit, bit = pcall(require, "bit")
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