The VideoLAN Forums

Posted: **27 May 2011 14:50**

I have collected some functions to simplify the work, some made by me and some made by others.
If someone has better alternatives, please post them.

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function string.substr(text, start, length)   -- by ale5000
	return text:sub(start, start - 1 + length)
end

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function string.charAt(text, pos)   -- by ale5000
	return text:sub(pos, pos)
end

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function string.setAt(text, pos, new_value)   -- by ale5000
	return text:sub(1, pos - 1)..new_value..text:sub(pos + 1)
end

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function string.lastIndexOf(text, search)   -- by ale5000
	local start, last_pos = 0
	while start ~= nil do
		last_pos = start
		start = text:find(search, start + 1, true)
	end

	if last_pos == 0 then return nil end
	return last_pos
end

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function string.trim_spaces(text)   -- by ale5000
	return text:gsub("^%s*(.-)%s*$", "%1")
end

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function string.skip_bytes(data, bytes)   -- by ale5000
	return data:sub(bytes + 1)
end

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-- Returns a string that has the internal numerical code equal of the number passed
function math.number_to_binary_code(in_number)   -- by ale5000
	if in_number == 0 then return "\0" end

	local out_string = ""
	while in_number > 0 do
		out_string = string.char(in_number % 256)..out_string
		in_number = math.floor(in_number / 256)
	end
	return out_string
end

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-- Returns a number with the internal numerical code of the string passed
function string.binary_code_to_number(in_string)   -- by ale5000
	local len, i, out_number = in_string:len() + 1, 0, 0
	while len > 1 do
		len = len - 1
		out_number = in_string:sub(len, len):byte() * (256^i) + out_number
		i = i + 1
	end
	return out_number
end

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function string.hex_string_to_binary_code(in_string)   -- by ale5000
	local len, out_string = in_string:len() + 1, ""
	while len > 2 do
		len = len - 2
		out_string = string.char( "0x"..in_string:substr(len, 2) )..out_string
	end
	return out_string
end

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function string.size_should_be(binary, required_length)   -- by ale5000
	local len_to_add = required_length - binary:len()
	if len_to_add < 0 then vlc.msg.err("size should be: The string is too long => "..binary) binary = "" len_to_add = required_length end

	while len_to_add > 0 do
		binary = "\0"..binary
		len_to_add = len_to_add - 1
	end
	return binary
end

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function string.size_should_be__add_to_right(binary, required_length)   -- by ale5000
	local len_to_add = required_length - binary:len()
	if len_to_add < 0 then vlc.msg.err("size should be, add to right: The string is too long => "..binary) binary = "" len_to_add = required_length end

	while len_to_add > 0 do
		binary = binary.."\0"
		len_to_add = len_to_add - 1
	end
	return binary
end

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function string.add_length(in_string)   -- by ale5000
	if in_string == "" then return "" end
	return math.number_to_binary_code(in_string:len() + 4):size_should_be(4)..in_string   -- The length of the length itself is included
end

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function string.add_length_x_byte(in_string, size_of_length)   -- by ale5000
	return math.number_to_binary_code(in_string:len()):size_should_be(size_of_length)..in_string
end

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function string.base64_decode(data)   -- by Alex Kloss <alexthkloss AT web.de>
	local b = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
	data = string.gsub(data, '[^'..b..'=]', '')
	return (data:gsub('.', function(x)
		if x == '=' then return '' end
		local r,f='',(b:find(x)-1)
		for i=6,1,-1 do r=r..(f%2^i-f%2^(i-1)>0 and '1' or '0') end
		return r;
	end):gsub('%d%d%d?%d?%d?%d?%d?%d?', function(x)
		if #x ~= 8 then return '' end
		local c=0
		for i=1,8 do c=c+(x:sub(i,i)=='1' and 2^(8-i) or 0) end
		return string.char(c)
	end))
end

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function bitwise_xor(x, y)   -- by Arno Wagner <arno AT wagner.name>
	if x == nil or y == nil then vlc.msg.err("Bitwise XOR: You cannot pass a nil value") return nil end
	local z = 0
	for i = 0, 31 do
		if x % 2 == 0 then			-- x had a '0' in bit i
			if y % 2 == 1 then		-- y had a '1' in bit i
				y = y - 1
				z = z + 2 ^ i		-- set bit i of z to '1'
			end
		else						-- x had a '1' in bit i
			x = x - 1
			if y % 2 == 0 then		-- y had a '0' in bit i
				z = z + 2 ^ i		-- set bit i of z to '1'
			else
				y = y - 1
			end
		end
		y = y / 2
		x = x / 2
	end
	return z
end

Posted: **28 May 2011 10:49**

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do
  local t = {
    ["0"] = "0000",
    ["1"] = "0001",
    ["2"] = "0010",
    ["3"] = "0011",
    ["4"] = "0100",
    ["5"] = "0101",
    ["6"] = "0110",
    ["7"] = "0111",
    ["8"] = "1000",
    ["9"] = "1001",
    a = "1010",
    b = "1011",
    c = "1100",
    d = "1101",
    e = "1110",
    f = "1111"
  };

--- Converts the given number, n, to a string in a binary number format (12
-- becomes "1100").
-- @param n Number to convert.
-- @return String in binary format.
  function tobinary(n)
    assert(tonumber(n), "number expected");
    return (("%x"):format(n):gsub("%w", t):gsub("^0*", ""));
  end
end

Your hexstring_to_binary function can be derived from the above.

Posted: **10 Jan 2021 21:01**

Timer

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-- sleep function, from:
-- http://lua-users.org/wiki/SleepFunction 
function sleep(s)
  local ntime = os.time() + s
  repeat until os.time() > ntime
end

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[LUA] Useful functions

[LUA] Useful functions

Re: [] Useful LUA functions

Re: [LUA] Useful functions