util.dbuffer: Add efficient shortcuts for discard() in certain cases
If the buffer is already empty, nothing to do. If we're throwing away the
whole buffer, we can just empty it and avoid read_chunk() (which in turn
may collapse()). These shortcuts are much more efficient.
local s_char = string.char;
local s_format = string.format;
local s_gsub = string.gsub;
local s_lower = string.lower;
local char_to_hex = {};
local hex_to_char = {};
do
local char, hex;
for i = 0,255 do
char, hex = s_char(i), s_format("%02x", i);
char_to_hex[char] = hex;
hex_to_char[hex] = char;
end
end
local function to(s)
return (s_gsub(s, ".", char_to_hex));
end
local function from(s)
return (s_gsub(s_lower(s), "%X*(%x%x)%X*", hex_to_char));
end
return {
encode = to, decode = from;
-- COMPAT w/pre-0.12:
to = to, from = from;
};