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-- Text processing functions.
local M = {}
local alphabet = '0123456789ABCDEF'
local atoi = {} ---@type table<string, integer>
local itoa = {} ---@type table<integer, string>
do
for i = 1, #alphabet do
local char = alphabet:sub(i, i)
itoa[i - 1] = char
atoi[char] = i - 1
atoi[char:lower()] = i - 1
end
end
--- Hex encode a string.
---
--- @param str string String to encode
--- @return string : Hex encoded string
function M.hexencode(str)
local enc = {} ---@type string[]
for i = 1, #str do
local byte = str:byte(i)
enc[2 * i - 1] = itoa[math.floor(byte / 16)]
enc[2 * i] = itoa[byte % 16]
end
return table.concat(enc)
end
--- Hex decode a string.
---
--- @param enc string String to decode
--- @return string? : Decoded string
--- @return string? : Error message, if any
function M.hexdecode(enc)
if #enc % 2 ~= 0 then
return nil, 'string must have an even number of hex characters'
end
local str = {} ---@type string[]
for i = 1, #enc, 2 do
local u = atoi[enc:sub(i, i)]
local l = atoi[enc:sub(i + 1, i + 1)]
if not u or not l then
return nil, 'string must contain only hex characters'
end
str[(i + 1) / 2] = string.char(u * 16 + l)
end
return table.concat(str), nil
end
return M
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