Pure Lua bitwise operations library compatible with Lua BitOp/LuaJIT

bit.lua

--[[
This file provides a library for bitwise operations. It is intended to
be compatible with Lua BitOp which itself is intended to be compatible
with the "bit" library bundled with LuaJIT. It is *not* compatible with
the "bit32" library bundled with Lua 5.2 and higher. For usage, consult
the Lua BitOp documentation:
https://bitop.luajit.org/api.html
https://bitop.luajit.org/semantics.html
]]
local string_format = string.format
local math_floor = math.floor
local select = select
return {
	tobit = function(x)
		x = x%(2^32)
		if x >= 2^31 then
			return x-2^32
		end
		return x
	end,
	tohex = function(x, n)
		if n == nil then
			n = 8
		elseif n < 0 then
			n = -n
			x = x%(2^(n*4))
			x = string_format("%0"..n.."X", x)
			return x
		end
		x = x%(2^(n*4))
		x = string_format("%0"..n.."x", x)
		return x
	end,
	bnot = function(x)
		x = x%(2^32)
		local output = 0
		for i=0, 31 do
			if x%2 == 0 then
				output = output+2^i
			end
			x = math_floor(x/2)
		end
		if output >= 2^31 then
			output = output-2^32
		end
		return output
	end,
	bor = function(...)
		local output = 0
		local bits = {}
		for i=1, select("#", ...) do
			local x = select(i, ...)
			x = x%(2^32)
			for i=1, 32 do
				if x%2 ~= 0 and bits[i] == nil then
					bits[i] = true
					output = output+2^(i-1)
				end
				x = math_floor(x/2)
			end
		end
		if output >= 2^31 then
			output = output-2^32
		end
		return output
	end,
	band = function(...)
		local output = 2^32-1
		local bits = {}
		for i=1, select("#", ...) do
			local x = select(i, ...)
			x = x%(2^32)
			for i=1, 32 do
				if x%2 == 0 and bits[i] == nil then
					bits[i] = true
					output = output-2^(i-1)
				end
				x = math_floor(x/2)
			end
		end
		if output >= 2^31 then
			output = output-2^32
		end
		return output
	end,
	bxor = function(...)
		local bits = {}
		for i=1, select("#", ...) do
			local x = select(i, ...)
			x = x%(2^32)
			for i=1, 32 do
				if x%2 ~= 0 then
					bits[i] = not bits[i]
				end
				x = math_floor(x/2)
			end
		end
		local output = 0
		for i=1, 32 do
			if bits[i] == true then
				output = output+2^(i-1)
			end
		end
		if output >= 2^31 then
			output = output-2^32
		end
		return output
	end,
	lshift = function(x, n)
		x = x%(2^32)
		n = n%32
		x = x*(2^n)
		x = x%(2^32)
		if x >= 2^31 then
			x = x-2^32
		end
		return x
	end,
	rshift = function(x, n)
		x = x%(2^32)
		n = n%32
		for i=1, n do
			x = math_floor(x/2)
		end
		if x >= 2^31 then
			x = x-2^32
		end
		return x
	end,
	arshift = function(x, n)
		x = x%(2^32)
		n = n%32
		local extension = 0
		if x >= 2^31 then
			extension = 2^31
		end
		for i=1, n do
			x = math_floor(x/2)+extension
		end
		if x >= 2^31 then
			x = x-2^32
		end
		return x
	end,
	rol = function(x, n)
		x = x%(2^32)
		n = n%32
		for i=1, n do
			x = x*2
			if x >= 2^32 then
				x = x%(2^32)+1
			end
		end
		if x >= 2^31 then
			x = x-2^32
		end
		return x
	end,
	ror = function(x, n)
		x = x%(2^32)
		n = n%32
		for i=1, n do
			local msb = 0
			if x%2 ~= 0 then
				msb = 2^31
			end
			x = math_floor(x/2)+msb
		end
		if x >= 2^31 then
			x = x-2^32
		end
		return x
	end,
	bswap = function(x)
		x = x%(2^32)
		local b1 = math_floor(x/0x1000000)
		local b2 = math_floor(x/0x10000)%0x100
		local b3 = math_floor(x/0x100)%0x100
		local b4 = x%0x100
		x = b4*0x1000000+b3*0x10000+b2*0x100+b1
		if x >= 2^31 then
			x = x-2^32
		end
		return x
	end,
}
--[[
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bit_test.lua

#!/usr/bin/env luajit
local fake_bit = dofile("./bit.lua")
local function capture_vararg(...)
	return {...}, select("#", ...)
end
local tobit
if bit ~= nil then
	tobit = bit.tobit
else
	tobit = fake_bit.tobit
end
local tests = {
	-- https://bitop.luajit.org/api.html
	{"tobit", {0xffffffff}, {-1}},
	{"tobit", {0xffffffff+1}, {0}},
	{"tobit", {2^40+1234}, {1234}},
	{"tohex", {1}, {"00000001"}},
	{"tohex", {-1}, {"ffffffff"}},
	{"tohex", {0xffffffff}, {"ffffffff"}},
	{"tohex", {-1, -8}, {"FFFFFFFF"}},
	{"tohex", {0x21, 4}, {"0021"}},
	{"tohex", {0x87654321, 4}, {"4321"}},
	{"bnot", {0}, {-1}},
	{"bnot", {-1}, {0}},
	{"bnot", {0xffffffff}, {0}},
	{"bnot", {0x12345678}, {tobit(0xedcba987)}},
	{"bor", {1, 2, 4, 8}, {15}},
	{"band", {0x12345678, 0xff}, {tobit(0x00000078)}},
	{"bxor", {0xa5a5f0f0, 0xaa55ff00}, {tobit(0x0ff00ff0)}},
	{"lshift", {1, 0}, {1}},
	{"lshift", {1, 8}, {256}},
	{"lshift", {1, 40}, {256}},
	{"rshift", {256, 8}, {1}},
	{"rshift", {-256, 8}, {16777215}},
	{"arshift", {256, 8}, {1}},
	{"arshift", {-256, 8}, {-1}},
	{"lshift", {0x87654321, 12}, {tobit(0x54321000)}},
	{"rshift", {0x87654321, 12}, {tobit(0x00087654)}},
	{"arshift", {0x87654321, 12}, {tobit(0xfff87654)}},
	{"rol", {0x12345678, 12}, {tobit(0x45678123)}},
	{"ror", {0x12345678, 12}, {tobit(0x67812345)}},
	{"bswap", {0x12345678}, {tobit(0x78563412)}},
	{"bswap", {0x78563412}, {tobit(0x12345678)}},
}
for i=1, #tests do
	local test = tests[i]
	local func_name = test[1]
	local func_fake = fake_bit[func_name]
	local arguments = test[2]
	for i=1, #arguments do
		local argument = arguments[i]
		-- https://bitop.luajit.org/semantics.html#undefined
		assert(argument ~= 1/0)
		assert(argument ~= -1/0)
		assert(argument == argument)
		assert(argument <= 2^51)
		assert(argument >= -(2^51))
		assert(argument%1 == 0)
	end
	local expected_retvals = test[3]
	if expected_retvals == nil then
		local func_real = bit[func_name]
		expected_retvals = {func_real(unpack(arguments))}
	elseif bit ~= nil then
		local func_real = bit[func_name]
		local actual_retvals = {func_real(unpack(arguments))}
		for j=1, math.max(#actual_retvals, #expected_retvals) do
			local actual_retval = actual_retvals[j]
			local expected_retval = expected_retvals[j]
			if actual_retval ~= expected_retval then
				error(string.format("for test %u for function %q expected retval %u was %q but ground truth is actually %q", i, func_name, j, tostring(expected_retval), tostring(actual_retval)))
			end
		end
	end
	if func_fake == nil then
		print(string.format("failed test %u for function %q because fake function didn't exist", i, func_name))
	else
		local actual_retvals = {func_fake(unpack(arguments))}
		for j=1, math.max(#actual_retvals, #expected_retvals) do
			local actual_retval = actual_retvals[j]
			local expected_retval = expected_retvals[j]
			if actual_retval ~= expected_retval then
				print(string.format("failed test %u for function %q because retval %u was expected to be %q but was actually %q", i, func_name, j, tostring(expected_retval), tostring(actual_retval)))
			end
		end
	end
end
print("done")