Re: Pure Lua tables

[Dirk Laurie <dirk.laurie@...>]

I suppose you mean luaH_getint which is where the switch sends you for
an integer key.

Read carefully.

There are two lines that check whether the index is in the range of
the array part. Only if it is not in there does control flow reach a
hash computation.

2017-10-15 19:05 GMT+02:00 Soni L. <fakedme@gmail.com>:
>
>
> On 2017-10-15 02:58 PM, Dirk Laurie wrote:
>>
>> 2017-10-15 17:43 GMT+02:00 Soni L. <fakedme@gmail.com>:
>>>
>>> I'm reading the Lua code, and it seems that Lua always checks the hash
>>> part,
>>> even for tables that don't use it. Why is this?
>>
>> That's not how I read the code. Here are the comments and return
>> statements of luaH_next.
>>
>>    /* find original element */
>>    /* try first array part */
>>    /* a non-nil value? */
>>   ...
>>        return 1;
>>      }
>>    /* hash part */
>>    /* a non-nil value? */
>>   ...
>>        return 1;
>> ...
>>    return 0;  /* no more elements */
>>
>> It's quite possible to return without reaching the code dealing with
>> the hash part.
>>
>
> Look at luaH_get. e.g. t[1] always checks hash part which does have a cost.
> the only way to avoid that cost is to fill the array part: if you have 256
> possible values, you need to fill t[1] to t[256]. and ofc t[0] always goes
> to the hash part so you also need to shift by one if 0 is a valid index.
>
>
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