Hacker News Reader

Jesus christ, 40% waste in arrays that can be solved by using `__attribute__((packed))`.

Irresponsible of them of not advertising this as an option in luaconf.h

Here's the rest of that paragraph for you:

"However, this attribute is a gcc extension not present in ISO C. Moreover, even in gcc it is not guaranteed to work [3]. As portability is a hallmark of Lua, this almost magical solution is a no-go."

`__attribute__((packed))` wouldn't help here since the issue is about Lua's array/hash hybrid table design and memory allocation strategy, not C struct padding.

But it did help in the other way, in my reading of the paper [1]. So the OP is asking why this is not even an option on supported environments, and I too think that this is indeed a good question to ask.

[1] "Hugo Gualandi reported that just adding the gcc attribute __attribute__((packed)) to the definition of the structure TValue reduces its size from 16 to 9 bytes, without any sensible difference in performance."

We figured that it wasn't worth dealing with the hassle of unaligned addresses because the more portable alternatives worked just as well.

Reply on news.ycombinator.com