Re: native code for bitwise operators in LUA

[Patrick Rapin <toupie300@...>]

> local idx = param[4] & 7
> TileCache[idx] = {
>    Format = TextureFormat[param[1] >> 5],
>    Size = (param[1] >> 3) & 3,
>    Line = ((param[1] & 3) << 7) | (param[2] >> 1),
>    TMem = ((param[2] & 1) << 8) | param[3],
>    Palette = param[5] >> 4,
>    TFlags = (param[5] >> 2) & 3,
>    TMask = ((param[5] & 3) << 2) | (param[6] >> 6),
>    TShift = (param[6] >> 2) & 15,
>    SFlags = param[6] & 3,
>    SMask = param[7] >> 4,
>    SShift = param[7] & 0xF }
>
> Trying to port it to using the
> bit library is very error-prone and makes the code even more ugly and
> hard to follow.

Not necessarily. Using bit32.extract, I even think it may because
easier to understand.
Supposing that param[1] contains the 4 high bytes and param[2] the low
bytes, your code become:

local extract = bit32.extract

local idx = extract(param[2], 0, 3)
TileCache[idx] = {
   Format = TextureFormat[extract(param[1], 29, 3)],
   Size = extract(param[1], 27, 2),
   Line = extract(param[1], 17, 8),
   TMem = extract(param[1], 8, 9),
   Palette = extract(param[2], 28, 4),
   TFlags = extract(param[2], 26, 2),
   TMask = extract(param[2], 22, 4),
   TShift = extract(param[2], 18, 4),
   SFlags = extract(param[2], 16, 2),
   SMask = extract(param[2], 12, 4),
   SShift = extract(param[2], 8, 4)}