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.
-- Only the operators needed by net.websocket.frames are provided at this point
return {
band = function (a, b, ...)
local ret = a & b;
if ... then
for i = 1, select("#", ...) do
ret = ret & (select(i, ...));
end
end
return ret;
end;
bor = function (a, b, ...)
local ret = a | b;
if ... then
for i = 1, select("#", ...) do
ret = ret | (select(i, ...));
end
end
return ret;
end;
bxor = function (a, b, ...)
local ret = a ~ b;
if ... then
for i = 1, select("#", ...) do
ret = ret ~ (select(i, ...));
end
end
return ret;
end;
rshift = function (a, n) return a >> n end;
lshift = function (a, n) return a << n end;
};